Two routes to functional adaptation: Tibetan and Andean high-altitude natives

Om hvordan pusten endres når man bor i høyland. Nevner mye om oksygentilgjengelighet, oksygenkaskade, hypoxi, kapillærer, mitokondrier, m.m., og om hvorfor vi har lite oksygen i mitokondriene. Studier undersøker spesifikt om at tibetanere har endrede gener siden de med gener som er tilpasset lave oksygennivåer har mindre fysiologisk stress og dermed større sjangse for barn som overlever, og hvilke forkjeller i hypoxi-tilpasning som har sjedd i de to befolkningene.

Ny, som må gjennomgåes: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1876443/

http://www.pnas.org/content/104/suppl.1/8655.full

These reveal generally more genetic variance in the Tibetan population and more potential for natural selection. There is evidence that natural selection is ongoing in the Tibetan population, where women estimated to have genotypes for high oxygen saturation of hemoglobin (and less physiological stress) have higher offspring survival.

At 4,000-m elevation, every breath of air contains only ≈60% of the oxygen molecules in the same breath at sea level. This is a constant feature of the ambient environment to which every person at a given altitude is inexorably exposed. Less oxygen in inspired air results in less oxygen to diffuse into the bloodstream to be carried to the cells for oxygen-requiring energy-producing metabolism in the mitochondria.

Humans do not store oxygen, because it reacts so rapidly and destructively with other molecules. Therefore, oxygen must be supplied, without interruption, to the mitochondria and to the ≥1,000 oxygen-requiring enzymatic reactions in various cells and tissues (4).


Fig. 1. Ambient oxygen levels, measured by the partial pressure of oxygen (solid line) or as a percent of sea-level values (dashed line), decrease with increasing altitude, a situation called high-altitude or hypobaric hypoxia. The atmosphere contains ≈21% oxygen at all altitudes.

The oxygen level is near zero in human mitochondria at all altitudes (5). This condition is described as “primitive,” because it has changed little for the past 2.5 billion years despite wide swings in the amount of atmospheric oxygen (at times it has been 10,000-fold lower; refs. 6 and 7) and “protective” in the sense that it circumvents potentially damaging reactions of oxygen with other molecules (8).


Fig. 2. The oxygen transport cascade at sea level (solid line) and at the high altitude of 4,540 m (dashed line) illustrates the oxygen levels at the major stages of oxygen delivery and suggests potential points of functional adaptation (data from ref. 60).

Potential and Actual Points of Adaptation to Hypoxia

Energy Production.

Lowlanders traveling to high altitude display homeostatic responses to the acute severe hypoxia. The responses are energetically costly, as indicated by an increase in basal metabolic rate (BMR; the minimum amount of energy needed to maintain life with processes such as regulating body temperature, heart rate, and breathing). BMR is increased by ≈17–27% for the first few weeks upon exposure to high altitude and gradually returns toward sea-level baseline (9). In other words, for acutely exposed lowlanders, the fundamental physiological processes required to sustain life at high altitude require more oxygen despite lower oxygen availability.

In contrast to acutely exposed lowlanders and despite the equally low level of oxygen pressure in the air and lungs, both Andean and Tibetan highlanders display the standard low-altitude range of oxygen delivery from minimal to maximal. Both populations have the normal basal metabolic rate expected for their age, sex, and body weight (1416), implying that their functional adaptations do not entail increased basal oxygen requirements. Furthermore, Andean and Tibetan highlanders have maximal oxygen uptake expected for their level of physical training (12, 13, 17).

Ventilation.

One potential point of adaptation in oxygen delivery is ventilation, which, if raised, could move a larger overall volume of air and achieve a higher level of oxygen in the alveolar air (Fig. 2) and diffusion of more oxygen. An immediate increase in ventilation is perhaps the most important response of lowlanders acutely exposed to high altitude, although it is not sustained indefinitely and is not found among members of low-altitude populations born and raised at high altitude, such as Europeans or Chinese (3, 18).

For example, a comparative analysis summarizing the results of 28 samples of Tibetan and Andean high-altitude natives at an average altitude of ≈3,900 m reported an estimated resting ventilation of 15.0 liters/min among the Tibetan samples as compared with 10.5 liters/min among the Andean samples (19).

Fig. 3 illustrates the higher resting ventilation of Tibetans as compared with Andean highlanders evaluated using the same protocol at ≈4,000 m. The mean resting ventilation for Tibetans was >1 SD higher than the mean of the Andean highlanders (20).

Oxygen in the Bloodstream.

The higher ventilation levels among Tibetans that move more oxygen through the lungs, along with the higher HVRs that respond more vigorously to fluctuations in oxygen levels, might be expected to result in more oxygen in the bloodstream. However, the level of oxygen in the arterial blood (Fig. 2) of a sample of Tibetans at ≈3,700 m was lower than that of a sample of Andean high-altitude natives at the same altitude (54 as compared with 57 mmHg; 1 mmHg = 133 Pa) (24, 25). In addition, hemoglobin, the oxygen-carrying molecule in blood, is less saturated with oxygen among Tibetans than among their Andean counterparts (26, 27). Fig. 3 illustrates the lower percent of oxygen saturation of hemoglobin in a sample of Tibetans at ≈4,000 m. The increased breathing of Tibetans does not deliver more oxygen to the hemoglobin in the arteries.

Fig. 3 illustrates the markedly lower hemoglobin concentrations in a sample of Tibetan men and women as compared with their Andean counterparts at ≈4,000 m. [The average hemoglobin concentrations were 15.6 and 19.2 g/dl for Tibetan and Andean men, respectively, and 14.2 and 17.8 g/dl for women (28).] Hemoglobin concentration is influenced by many factors, including erythropoietin, a protein that causes differentiation of the precursors that will become hemoglobin-containing red blood cells. Tibetans have slightly lower erythropoietin concentrations than Andean highlanders at the same altitude (25). When matched for volume of red blood cells, a procedure that would effectively compare the highest Tibetan and the lowest Andean values, Andean highlanders have much higher erythropoietin levels, which implies that some sensor is responding as if the stress were more severe, even though the samples were collected at the same altitude of ≈3,700 m.

Andean highlanders have overcompensated for ambient hypoxia according to this measure, whereas Tibetan highlanders have undercompensated. Indeed, Tibetans are profoundly hypoxic and must be engaging other mechanisms or adapting at different points in the oxygen transport cascade to sustain normal aerobic metabolism.

Fig. 4. The calculated arterial oxygen content of Tibetan men and women is profoundly lower than their Andean counterparts measured at ≈4,000 m (data from ref. 62), whereas the exhaled NO concentration is markedly higher (recalculated from data reported in ref. 34).

Blood Flow and Oxygen Diffusion.

Other potential points of functional adaptation include the rate of flow of oxygen-carrying blood to tissues and the rate of oxygen diffusion from the bloodstream into cells.

Because blood flow is a function of the diameter of blood vessels, dilating factors could, in principle, improve the rate of oxygen delivery. Sea-level populations respond to high-altitude hypoxia by narrowing the blood vessels in their lungs, the first point of contact with the circulation. Known as hypoxic pulmonary vasoconstriction, that reflex evolved at sea level to direct blood away from temporarily poorly oxygenated toward better oxygenated parts of the lung. High-altitude hypoxia causes poor oxygenation of the entire lung and general constriction of blood vessels to the degree that it raises pulmonary blood pressure, often to hypertensive levels (3, 29).

In contrast, most Tibetans do not have hypoxic pulmonary vasoconstriction or pulmonary hypertension. This is indicated by essentially normal pulmonary blood flow, as measured by normal or only minimally elevated pulmonary artery pressure (29, 30).

a mean pulmonary artery pressure of 31 mmHg for the Tibetan 28% lower than the mean of 43 mmHg for the Andean (35 mmHg is often considered the upper end of the normal sea-level range) (30, 31). Andean highlanders are consistently reported to have pulmonary hypertension (29). Thus, pulmonary blood flow is another element of oxygen delivery for which Tibetans differ from Andean highlanders in the direction of greater departure from the ancestral response to acute hypoxia.

A probable reason for the normal pulmonary artery pressure among Tibetans is high levels of the vasodilator nitric oxide (NO) gas synthesized in the lining of the blood vessels. Low-altitude populations acutely exposed to high-altitude down-regulate NO synthesis, a response thought to contribute to hypoxic pulmonary vasoconstriction (32, 33). In contrast, NO is substantially elevated in the lungs of Tibetan as compared with Andean highlanders and lowlanders at sea level (Fig. 4) (34). Among Tibetans, higher exhaled NO is associated with higher blood flow through the lungs (30).

Several other lines of evidence highlight the importance of high blood flow for Tibetans. These include greater increase in blood flow after temporary occlusion (35) and higher blood flow to the brain during exercise (36) as compared with lowlanders.

Generally, Tibetans appear to have relatively high blood flow that may contribute significantly to offsetting their low arterial oxygen content.

A denser capillary network could potentially improve perfusion and oxygen delivery, because each capillary would supply a smaller area of tissue, and oxygen would diffuse a shorter distance. Tibetans (the study sample were Sherpas, an ethnic group that emigrated from Tibet to Nepal ≈500 years ago) who are born and raised at high altitude have higher capillary density in muscles as compared with Andean high-altitude natives, Tibetans born and raised at low altitude, or lowlanders (Fig. 5) (40).


Fig. 5. High-altitude native Tibetans have higher capillary density than their Andean counterparts or populations at low altitude; Tibetan and Andean highlanders both have lower mitochondrial volume than low-altitude populations (data from refs. 40, 44, 63, and64).

The last potential point of adaptation is at the level of the mitochondrion itself. Acutely exposed lowlanders lose mitochondria in leg muscles during the first 3 weeks at altitude. Similarly, both Tibetan (Sherpas) and Andean high-altitude natives have a lower mitochondrial volume in leg muscle tissue than sea-level natives at sea level (Fig. 5) (40).

Among Tibetans, a smaller mitochondrial volume somehow supports a relatively larger oxygen consumption, perhaps by higher metabolic efficiency (12, 43, 44).

Another candidate gene is the transcription factor hypoxia-inducible factor 1 (HIF1) often called the “master regulator” of oxygen homeostasis, because it induces >70 genes that respond to hypoxia (5658). An investigation of polymorphisms in the HIF1A gene of Tibetans (Sherpas) found a dinucleotide repeat in 20 Tibetans that was not found in 30 Japanese lowlander controls (59).

Differences in the control of breathing between Himalayan and sea-level residents

Om hvordan langvarig høydeopphold utvisker sensitiviteten til CO2.

http://jp.physoc.org/content/588/9/1591.full

Highlanders had lower mean ± S.E.M.ventilatory sensitivities to CO2 than lowlanders at both isoxic tensions (hyperoxic: 2.3 ± 0.3 vs. 4.2 ± 0.3 l min−1 mmHg−1, P = 0.021; hypoxic: 2.8 ± 0.3 vs. 7.1 ± 0.6 l min−1mmHg−1, P < 0.001), and the usual increase in ventilatory sensitivity to CO2 induced by hypoxia in lowlanders was absent in highlanders (P = 0.361).

Furthermore, the ventilatory recruitment threshold (VRT) CO2 tensions in highlanders were lower than in lowlanders (hyperoxic: 33.8 ± 0.9 vs. 48.9 ± 0.7 mmHg, P < 0.001; hypoxic: 31.2 ± 1.1 vs. 44.7 ± 0.7 mmHg, P < 0.001).

We conclude that control of breathing in Himalayan highlanders is distinctly different from that of sea-level lowlanders. Specifically, Himalayan highlanders have decreased central and absent peripheral sensitivities to CO2. Their response to hypoxia was heterogeneous, with the majority decreasing their VRT indicating either a CO2-independent increase in activity of peripheral chemoreceptor or hypoxia-induced increase in [H+] at the central chemoreceptor.

Control of breathing in humans can be broadly divided into chemoreflex and non-chemoreflex drives to breathe (Fig. 1) (Lloyd & Cunningham, 1963). Non-chemoreflex breathing stimuli include a wakefulness drive (Longobardo et al. 2002), voluntary (cortical) drive (Shea, 1996) and hormonal factors (Jensen et al. 2008), as well as neural and humoral mediating factors that are especially important in the control of breathing during exercise (Bell, 2006; Dempsey, 2006; Haouzi, 2006). The chemoreflex drive to breathe can be further divided into central and peripheral chemoreceptor drives. Both central and peripheral chemoreceptors respond to changes in the hydrogen ion concentration ([H+]) in their immediate environments (Torrance, 1996; Nattie & Li, 2009).

In contrast to the central chemoreceptors, peripheral chemoreceptors are also sensitive to changes in arterial Graphic (Graphic) via a hypoxia-mediated increase in their sensitivity to [H+] (Cunningham, 1987; Torrance, 1996; Kumar & Bin-Jaliah, 2007), and hyperoxia (Graphic ≥ 150 mmHg) effectively silences this response (Lloyd & Cunningham, 1963; Mohan & Duffin, 1997).

Central and peripheral chemoreceptor neural drives are integrated in the medulla to provide the total chemoreflex neural drive (Fink, 1961; Shea, 1996; Mohan & Duffin, 1997; Orem et al. 2002) that, in combination with non-chemoreflex drives, provides ventilatory drive to respiratory muscles.


Figure 3. Hypercapnic ventilatory response The graph displays two isoxic responses: hyperoxic (Graphic = 150 mmHg) representing central chemoreflex response, and hypoxic (Graphic = 50 mmHg) representing the addition of central and peripheral chemoreflexes responses. The slope of each isoxic response represents sensitivity of the chemoreflex to CO2. The inflection point at which ventilation starts to increase in response to increasing Graphic is the ventilatory recruitment threshold (VRT), where the chemoreflex neural drive to breathe exceeds a drive threshold and starts to produce an increase in pulmonary ventilation. Ventilation below VRT represents non-chemoreflex drives to breathe and is known as the basal ventilation. The differences in ventilation between isoxic rebreathing lines at any given isocapnic Graphic can be used to calculate the hypoxic ventilatory response (indicated by vertical arrows). Note that the choice of isocapnic Graphic affects the magnitude of the measured HVR even within the same subject (Duffin, 2007), with higher HVRs measured at higher isocapnic Graphicvalues in the illustrated example. Note also that the magnitude of HVR provides little information about the characteristics of the control of breathing model, as HVR magnitude is dependent on the combination of central and peripheral chemoreflex responses.

There was no difference in the non-chemoreflex drives to breathe between highlanders and lowlanders, as indicated by similar basal (below VRT) ventilations in the two populations (Table 2).

The highlanders had decreased VRTs compared to lowlanders during both hypoxic and hyperoxic rebreathing tests. The leftward shift of the VRTs in highlanders suggests that a lower Graphic was required to exceed the VRT in highlanders compared to lowlanders. Since both central and peripheral chemoreceptors are actually [H+] sensors, interpretation of this result should consider the acid–base status in both populations. According to the Henderson–Hasselbach equation (Nunn, 1993), the relationship between [H+] and Graphiccan be described as follows:Formulawhere [HCO3] is the bicarbonate ion concentration. In a hypothetical sea-level resident at sea-level, [H+] is approximately 40 nM l−1, Graphic is 40 mmHg and [HCO3] is 24 mM l−1. At altitude, hypoxia-induced hyperventilation results in a reduction of Graphic that leads to a reduction in [H+] and respiratory alkalosis according to the above equation. Highlanders compensate for respiratory alkalosis by presumably reducing their [HCO3] through increased renal excretion, thereby restoring the Graphic/[HCO3] ratio to sea-level values and normalizing [H+].

For example, if hypoxia-induced hyperventilation reduced CO2 from 40 to 30 mmHg, and HCO3− fell from 24 to 18 mM l−1, then the overall ratio of CO2/HCO3− would be maintained at 5/3 as in sea-level lowlanders, but normal [H+] of 40 nM l−1 would be achieved at a lower Graphic of 30 mmHg rather than 40 mmHg, as at sea-level. Considering that the highlanders in our study have an adapted acid–base status (Santolaya 1989), the observed difference in VRTs can be explained by the altered [H+]–Graphic relationship in highlanders compared to lowlanders, with the assumption that the chemoreceptor thresholds [H+] are similar (Duffin, 2005).

The sensitivity of the central chemoreceptor to CO2, as indicated by the ventilatory sensitivity during hyperoxic rebreathing, was lower in highlanders compared to lowlanders (2.5 ± 0.4 vs. 4.2 ± 0.3 l min−1 mmHg−1, P = 0.011). Hyperoxia effectively silences the peripheral chemoreceptor (Lloyd & Cunningham, 1963; Mohan & Duffin, 1997), and therefore the ventilatory sensitivity measured during hyperoxic rebreathing can be taken as a measure of central chemoreceptor sensitivity (Duffin, 2007).

Since the ventilatory response to hypercapnia decreases with age (Nishimura et al. 1991; Jones et al. 1993; Poulin et al.1993; McGurk et al. 1995) and increases with weight (Marcus et al. 1994), the observed lower central CO2 chemosensivity in our highlander subjects may be the result of their older age and smaller body size.

Ventilatory response to hypoxia in highlanders was markedly different from that in lowlanders. Unlike lowlanders, who responded to hypoxia by increasing the sensitivity of their ventilatory response to CO2 (Mohan & Duffin, 1997), the highlanders seemed to decrease their VRT in response to hypoxia with no change in the sensitivity to CO2.

The ventilatory response to hypoxia in sea-level residents is mediated by peripheral chemoreceptors via an increase in the peripheral chemoreceptor sensitivity to [H+] (Cunningham, 1987; Torrance, 1996; Kumar & Bin-Jaliah, 2007). A lack of increase in ventilatory sensitivity to CO2 with induction of hypoxia in highlanders suggests that their peripheral chemoreceptors are relatively insensitive to CO2.

Other possible mechanisms of CO2-independent peripheral responses to hypoxia may include a hypoxia-induced increase in the carotid body tonic drive to breathe, changes in systemic hormonal mediators, an altered cerebral spinal fluid-buffering capacity at the central chemoreceptor or an alteration in cerebral vascular reactivity leading to a higher [H+] at central chemoreceptor.

Specifically, we showed that Himalayan highlanders have decreased central and absent peripheral chemoreceptor sensitivity to CO2, and that they are sensitive to hypoxia, albeit via a different mechanism than that observed in lowlanders at sea-level. A blunted central and an absent peripheral ventilatory sensitivity to CO2 in Himalayan highlanders may stabilize their ventilatory controller by reducing the overall gain in the feedback part of the controller circuit, thereby reducing altitude-related breathing instability (Ainslie & Duffin, 2009)

The non-chemoreflex drives to breathe were similar between Himalayan highlanders and sea-level lowlanders.

The role of nitric oxide in skin blood flow increases due to vibration in healthy adults and adults with type 2 diabetes

Vibrasjon på underamren øker blodsirkulasjon pga økt NO utskillelse fra blodkarveggene.

http://www.ncbi.nlm.nih.gov/pubmed/19132854

those with diabetes had significantly lower (223%; P = 0.003) skin blood flows compared to the healthy older adults (461%). The rate of NO production, expressed as microM NO . flux, also increased significantly in both groups after vibration (healthy group, 374%; diabetes group, 236%) and remained significantly elevated (healthy group, 258%; diabetes group, 177%) for at least 5 min

In vivo analys is of skin microcirc ulation and the role of nitric oxide dur ing vibration.

Nevner at vibrasjon (47Hz) øker blodsirkulasjonen i huden pga stimuli av NO i blodkar cellene. De viste dette fordi ved å gi forsøksdyrene en NO-hemmer fikk de ingen økning i blodsirkulasjon selv med vibrasjoner.

http://www.ncbi.nlm.nih.gov/pubmed/21918246

Studies in healthy volunteers and patients with renal failure have shown that vibration, applied with a frequency of 47 Hz and a vibrational intensity of 600 mVpp, increases microcirculation of blood in the skin.

Vibration significantly increased the blood flow at 5 and 15 minutes after application (P = 0.002 and P = 0.046, respectively). Differences between the control and experimental group also were statistically significant (P = 0.0017 and P = 0.046, respectively).

When NO synthase inhibitor L-NAME was administered, the increase in blood flow in the vibration group was minimal after 5 and 10 minutes, and nonexistent after 15 minutes.

Vascular Fasciatherapy Danis Bois Method: a Study on Mechanism Concerning the Supporting Point Applied on Arteries

Studie som nevner svært mye interessant om blodsirkulasjon, tensegritet og om bindevev. Den er rettet mot en spesifikk metode for spontan bevegelse, men har mye interessante teamer som gjelder andre bodyworkmetoder også.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3242644/

«Vascular research especially made a jump forward with the Nobel Prize awarded to Furchgott, Ignarro and Murad for having discovered the endogenous production of nitric oxide (NO). »

«Mesenchyme differentiates and generates every type of connective tissue and many organs in adults(3) including bone, muscle, and the middle layer of the skin, excepting nervous tissue and the digestive track(7).»

«In this study, one can notice that they are totally or partially at the origin of vascular endothelium and mesothelium (peritoneum, pleura, pericardium)(6). And this vascular endothelium is the origin of blood, which is also considered as specialized connective tissue(6).»

Forskjellen mellom arterier og kapillærer:
«Capillaries have the function of distributing blood in the body, bringing about an exchange between blood and tissues. Structurally, arteries carry and separate blood and tissues.»

«Fascia is a very sensitive tissue that detects any kind of stress — physical, emotional or psycho-social. It reacts by contracting and imprisoning the organs it covers, thus impairing their physiological functions. Furthermore, the tightening of their connective parts induces a perceptible disturbance in mobility and rhythm of these organs.»

«ECs respond to increased blood flow by causing relaxation of the surrounding VSMCs. VSMC relaxation in response to flow occurs over seconds to minutes and if high flow persists, remodeling of the artery wall enlarges the lumen over time in a period of weeks to months(36). Decreased flow induces vessel narrowing(37), and extreme low flow may lead to complete vessel regression, which involves apoptosis of the ECs(38).»

«The human body seems to be made of the only and same tissue which is functionally differentiated: there are only tissue connections, simply a histological continuum without any clear separation between the skin and hypodermis, the vessels, the aponeurosis, and the muscles(46). So connective tissue, its cells, MEC, and fibers are an obvious link in this construction.»

«The theory of tensegrity emerged from the interests of architects (from Richard Buckminster Fuller to Rene Motro) and biologists (Donald Ingber(47)), and their meeting point of connection with our discussion can be found in these definitions: “a type of prestressed structural network, composed of opposing tension and compression elements that self-stabilizes its shape through establishment of a mechanical force balance”, and “tensegrity is used to stabilize the shape of living cells, tissue and organs, as well as our whole bodies”(4). Hence, the use of this architectural system for structural organization provides a mechanism to physically integrate part and whole(4).»

«Arteries have a special relation with fascias. Connective tissue is present in the three tunics of the artery. Adventitia is a typical sheathing fascia, which becomes tense in reaction to stress. Media is an association of muscle and connective tissue reacting to local mechanical variations (i.e. blood pressure) or general influence (i.e. stress) by tensing and/or by contracting. Intima, whose endothelium can be assimilated to a very big autocrine/paracrine formation(48)reacting mainly to the influence of blood qualities (i.e. type of flow, components), lies on a connective layer underlining endothelium.»

Hypoxia-generated superoxide induces the development of the adhesion phenotype

Viktig studie om mekanismen bak hvordan hypoxi gir arrvev (adhesions) i kroppen. Relatert til hyperventilering vil lite CO2 gir hypoxi og sammen med trange blodkar vil de utsatte stedene i kroppen utvikle arrvev mellom muskler og nerver. Nevner hvordan antioksidanter er viktig for å unngå arrvev, spesielt etter operasjoner. Og motsatt, at oksidanter kan skape arrvev fra friskt vev. Nevner også hvordan nitratreaksjoner er med å skaper arrvev, så mulig at CO2 bidrar med å dempe nitratreaksjonene og dermed dempe dannelsen av arrvev. Den viser også at det kan være mulig å få arrvev celler om til å bli normale celler.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2574925/

«Adhesion fibroblasts exhibit higher TGF-β1 and type I collagen expression as compared to normal peritoneal broblasts. Furthermore, exposure of normal peritoneal fibroblasts to hypoxia results in an irreversible increase in TGF-β1 and type I collagen. We postulated that the mechanism by which hypoxia induced the adhesion phenotype is through the production of superoxide either directly or through the formation of peroxynitrite. »

«Hypoxia treatment resulted in a time-dependent increase in TGF-β1 and type I collagen mRNA levels in both normal peritoneal and adhesion fibroblasts.»

«In contrast, treatment with SOD, to scavenge endogenous superoxide, resulted in a decrease in TGF-β1 and type I collagen expression in adhesion fibroblasts to levels seen in normal peritoneal fibroblasts; no effect on the expression of these molecules was seen in normal peritoneal fibroblasts. »

«In conclusion, hypoxia, through the production of superoxide, causes normal peritoneal fibroblasts to acquire the adhesion phenotype. Scavenging superoxide, even in the presence of hypoxia, prevented the development of the adhesion phenotype. These findings further support the central role of free radicals in the development of adhesions.»

«Postoperative adhesions are a significant source of impaired organ functioning, decreased fertility, bowel obstruction, difficult reoperation, and possibly pain (1,2)

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Destroy user interface c»

«The processes that result in either normal peritoneal tissue repair or the development of adhesions include the migration, proliferation, and/or differentiation of several cell types, among them inflammatory, immune, mesothelial, and fibroblast cells (3)

«Hypoxia, resulting from tissue injury, has been suggested to play an important role in wound healing, and may therefore be a critical factor in the development of postoperative adhesions (4,7)

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Destroy user interface contrHypoxia is known to trigger the expression of TGF-β1, which consequently increases the expression of extracellular matrix proteins, including type I collagen (4) 

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Destroy user interface contr«Type I collagen synthesis has been shown to be crucially dependent on the availability of molecular oxygen in tissue culture, animal, and human wound healing experiments (8,9)

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Destroy user interface controlMoreover, exposure of normal peritoneal fibroblasts to hypoxia irreversibly induces TGF-β1 and type I collagen to levels seen in adhesion fibroblasts (4,10)

«Additionally, hypoxia is known to acutely promote superoxide (O2.−) generation from disparate intracellular sources that include xanthine dehydrogenase oxidase (11), mitochondrial electron transport chain (12), and NAD[P]H oxidase (13).

In biological systems, superoxide dismutase (SOD) protects against the deleterious actions of this radical by catalyzing its dismutation to hydrogen peroxide plus oxygen, (14) Whereas SOD breaks down O2.−, xanthine oxidase synthesizes O2.−. Xanthine oxidase appears to be one of the major superoxide-producing enzymes (14)«

«Scavenging superoxide restores both TGF-β1 and type I collagen mRNA levels in adhesion fibroblasts to levels observed in normal peritoneal fibroblasts»
«Normal peritoneal and adhesion fibroblasts treated with super-oxide dismutase, a O2.− scavenging enzyme, exhibited a dose–response decrease (0, 5, 10, 15, and 20 units/ml) in TGF-β1 and type I collagen mRNA levels in adhesion fibroblasts while not effecting normal peritoneal fibroblasts (Figs. 3A and B).»

«Scavenging superoxide during hypoxia exposure protects against the development of the adhesion phenotype»

«Peroxynitrite treatment increased the adhesion phenotype markers, TGF-β1 and type I collagen»

«Adhesion fibroblasts are myofibroblasts, defined as transiently activated fibroblasts exhibiting features intermediate between those of smooth muscle cells and fibroblasts, including the expression of α-SM actin (29,21) and a depleted antioxidant system (22). In normal wound healing, as the wound resolves, the cellularity decreases and the myofibroblasts disappear by apoptosis (23). However, in several pathological cases, including fibrosis, myofibroblastic differentiation persists and causes excessive scarring (24,25)

«This is further supported by the fact that when O2.− was scavenged, there was in a significant decrease in TGF-β1 and type I collagen in adhesion fibroblasts to levels seen in normal peritoneal fibroblasts. »

«Reactive oxygen species (ROS) are involved in TGF-β-stimulated collagen production in murine embryo fibroblasts (NIH3T3), and the effect of glutathione depletion on TGF-β-stimulated collagen production may be mediated by facilitating ROS signaling (37)

«Reactive oxygen and nitrogen intermediates control the synthesis of cytokines and growth factors in several in vitro models (40). For instance, they modulate the expression and/or release of monocyte chemoattractant protein-1 (41,42), tumor necrosis factor-α, interleukin (IL)-1 (43,44), IL-8 (45,46), platelet-derived growth factor (47,48), and TGF-β1 (49). «

«Adhesion fibroblasts exhibited a significantly lower level of nitric oxide (NO) and higher protein nitration as compared to normal peritoneal fibroblasts, although there was no difference in the iNOS expression level between the two cell lines (17,50,51). This strongly indicates that adhesion fibroblasts use NO to form ONOO−, and consequently their basal ONOO− levels are higher than normal peritoneal fibroblasts. «

«Thus, treatment with SOD might affect the homeostasis of myofibroblasts by inducing cell death or the phenotypic reversion of myofibroblasts into normal fibroblasts. »

«Our results clearly indicate that hypoxia generated O2.− is a key player in the formation of the adhesion phenotype. This became evident when normal peritoneal fibroblasts were treated with SOD under hypoxic conditions and no change in adhesion markers was seen.»


«In this model, hypoxia-generated O2.− exerts its effect directly by enhancing the expression of TGF-β1, which consequently leads to elevated levels of type I collagen, a hallmark of the adhesion phenotype.»

Carbon dioxide influence on nitric oxide production in endothelial cells and astrocytes: Cellular mechanisms

Viktig studie som nevner hvordan CO2 forholder seg til NO og vasodilasjon. Nevner mekanismene bak eNOS og nNOS og hva som faktisk skjer i cellene. Denne studien er på celler, men beskriver mye av det som skjer in vivo og refererer til andre viktige studier.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3073030/

«Cerebral vessels may regulate cerebral blood flow by responding to changes in carbon dioxide (CO2) through nitric oxide (NO) production. »

«NO levels in endothelial cells increased during hypercapnia by 36% in 8 hours and remained 25% above baseline. NO increase in astrocytes was 30% after 1 hour but returned to baseline at 8 hours. NLA blocked NO increase in endothelial cells under hypercapnia.»

«This study suggests that cerebral endothelial cells and astrocytes release NO under normocapnic conditions and NO production is increased during hypercapnia and decreased during hypocapnia independent of pH. Further, this demonstrates that endothelial cells may play a pivotal role in chemoregulation by modulating NOS activity.»

«Modulation of cerebral vascular tone in response to changes in the arterial partial pressure of carbon dioxide (pCO2) is defined as chemoregulation. In humans hypocapnia produces vasoconstriction resulting in decreased cerebral blood flow (CBF), whereas hypercapnia produces vasodilation and increased CBF (Lavi et al., 2003). »

«Using nitric oxide synthase (NOS) inhibitors, several in vivo studies have suggested that vasodilation in response to increased pCO2may be mediated by NO (Lavi et al., 2006). »

«Under hypercapnic conditions (pCO2 56.3±8.7 mmHg), NO concentration increased from baseline levels to a mean of 10±0.6×10-10M during the first 4 hours (Figure 1A). NO concentration peaked at 36% (10.2±0.5×10-10M) above baseline at 8 hours and stabilized 25% (9.4±0.5×10-10M) above baseline until completion of the experiment.»

«By plotting NO changes as a function of pCO2, we could disregard time as a variable in NO production (Figure 3) to establish that changes in NO levels correlate with changes in pCO2 (R=0.99).»

CO2 og NO

«Under hypercapnic conditions (pCO2 56.3±8.7 mmHg), human fetal astrocytes increased NO production by 30% over baseline values to a mean level of 2.5±1.2×10-10M in the first hour of hypercapnia (Figure 2). NO production then gradually decreased to control levels after 8 hours and remained at control levels for the remainder of the experiments.»

CO2 og NO i astrocytt

«The pH values were kept stable within a neutral gap under normocapnic (7.39±0.01), hypercapnic (7.36±0.02) and hypocapnic (7.40±0.01) conditions.»

» Stimulation of NOS in the endothelial cells is consistent with the NO-dependent vasodilation and increased CBF that occur in vivo during hypercapnia, as has been shown in rats (Iadecola, 1992) and in primates (Thompson et al., 1996). Decreased NO production by endothelial cells also correlates with the in vivo vasoconstrictive response to hypocapnia shown previously (Lavi et al., 2003;Thompson et al., 1996).»

«Thus, it is unlikely that eNOS is responsible for the early or fast phase response during chemoregulation in vivo. There are several explanations for this phenomenon. First, nitrite (NO2), being a storage pool of NO, can be reduced to NO under acidic and hypoxic conditions in vivo (Cosby et al., 2003). Under these conditions nitrite releases NO in the presence of deoxygenated hemoglobin in blood (Cosby et al., 2003;Nagababu et al., 2003) or neuroglobin (Burmester et al., 2000) in neurons acting as a nitrite reductase (Petersen et al., 2008). »

«The chemoregulatory response to CO2 changes in vivo is rapid, occurring on the order of milliseconds; our results did not demonstrate this component of the chemoregulatory response.»

«Cerebrovascular reactivity in response to CO2 is impaired in diabetic or hypertensive patients with endothelial dysfunction (Lavi et al., 2006), suggesting an important role for endothelial cells in modulating CBF response to CO2. »

«It has been reported that the ATP-sensitive K+ channels play a pivotal role in microvessel vasodilation of the cerebral cortex in response to decreased pH corresponding to mild hypercapnia and that a NOS inhibitor could not alter this vasodilation (Nakahata et al., 2003).»