Variation among arthropod taxa in the amino acid content of exoskeleton and digestible tissue.

Arthropod consumption provides amino acids to invertebrates and vertebrates alike, but not all amino acids in arthropods may be digestible as some are bound in the exoskeleton. Consumers may not be able to digest exoskeleton in significant amounts or avoid it entirely (e.g., extraoral digestion). Hence, measures that do not separate digestible amino acids from those in exoskeleton may not accurately represent the amino acids available to consumers. Additionally, arthropods are taxonomically diverse, and it remains unclear if taxonomic differences also reflect differences in amino acid availability. Thus, we tested: (1) if there were consistent differences in the content and balance of amino acids between the digestible tissue and exoskeleton of arthropods and (2) if arthropod Orders differ in amino acid content and balance. We measured the amino acid content (mg/100 mg dry mass) and balance (mg/100 mg protein) of whole bodies and exoskeleton of a variety of arthropods using acid hydrolysis. Overall, there was higher amino acid content in digestible tissue. There were also significant differences in the amino acid balance of proteins in digestible tissue and exoskeleton. Amino acid content and balance also varied among Orders; digestible tissues of Hemiptera contained more of some essential amino acids than other Orders. These results demonstrate that arthropod taxa vary in amino acid content, which could have implications for prey choice by insectivores. In addition, exoskeleton and digestible tissue content differ in arthropods, which means that whole body amino acid content of an arthropod is not necessarily a predictor of amino acid intake of a predator that feeds on that arthropod.

End points in pulmonary arterial hypertension: the way forward.

Pulmonary arterial hypertension is a rare disease of poor prognosis. Despite its rarity >1,000 patients have been randomised in placebo-controlled trials using novel therapies, including prostacyclin analogues, endothelin receptor antagonists and, most recently, phosphodiesterase 5 inhibitors. Nearly all of these trials have used exercise capacity, measured by the unencouraged 6-min walking distance, as the primary end point and a variety of other measurements as secondary end points. This approach has been productive, leading to the licensing of a number of effective treatments. Future clinical trials, however, will probably assess drug combinations, make comparisons between drugs and include less severely ill patients. It is, therefore, timely to examine the end points used. The authors discussed the various end points that have been used in the past and possible end points that might be used in the future. End points considered included measurements of: exercise capacity, haemodynamics, quality of life, imaging of the right heart and circulation, and chemical markers of pulmonary hypertension. Many of these show promise but will have to be used in parallel and compared with conventional end points such as the 6-min walking distance before their value can be demonstrated convincingly to the regulatory authorities.

Selective expansion of fibroblast subpopulations from pulmonary artery adventitia in response to hypoxia.

Proliferation of fibroblasts contributes to the adventitial thickening observed during the development of hypoxia-induced pulmonary hypertension. However, whether all or only specific subpopulations of fibroblasts proliferate during this process is unknown. Because lung, skin, and gingiva contain multiple fibroblast subpopulations, we hypothesized that the pulmonary artery (PA) adventitia of neonatal calves is composed of multiple fibroblast subpopulations and that only selective subpopulations expand under chronic hypoxic conditions. Fibroblast subpopulations were isolated from PA adventitia of control calves using limited dilution cloning techniques. These subpopulations exhibited marked differences in morphology, actin expression, and serum-stimulated growth. Only select fibroblast subpopulations demonstrated the ability to proliferate in response to hypoxia. Fibroblast subpopulations were similarly isolated from calves exposed to hypoxia (14 days). With regard to morphology, actin expression, and serum-stimulated growth of subpopulations, there were no obvious differences in fibroblast subpopulations between the hypoxic and the control calves. However, the number of fibroblast subpopulations with about a twofold increase in hypoxia-induced DNA synthesis was significantly greater in the hypoxic calves (26%) compared with control calves (10%). We conclude that the bovine PA adventitia comprises numerous phenotypically and biochemically distinct fibroblast subpopulations and that select subpopulations expand in response to chronic hypoxia.

Erythropoiesis in women during 11 days at 4,300 m is not affected by menstrual cycle phase.

Because the ovarian steroid hormones, progesterone and estrogen, have higher blood levels in the luteal (L) than in the follicular (F) phase of the menstrual cycle, and because of their known effects on ventilation and hematopoiesis, we hypothesized that less hypoxemia and less erythropoiesis would occur in the L than the F phase of the cycle after arrival at altitude. We examined erythropoiesis with menstrual cycle phase in 16 women (age 22.6 +/- 0.6 yr). At sea level, 11 of 16 women were studied during both menstrual cycle phases, and, where comparison within women was available, cycle phase did not alter erythropoietin (n = 5), reticulocyte count (n = 10), and red cell volume (n = 9). When all 16 women were taken for 11 days to 4,300-m altitude (barometric pressure = 462 mmHg), paired comparisons within women showed no differences in ovarian hormone concentrations at sea level vs. altitude on menstrual cycle day 3 or 10 for either the F (n = 11) or the L (n = 5) phase groups. Arterial oxygen saturation did not differ between the F and L groups at altitude. There were no differences by cycle phase on day 11 at 4,300 m for erythropoietin [22.9 +/- 4.7 (L) vs. 18.8 +/- 3.4 mU/ml (F)], percent reticulocytes [1.9 +/- 0.1 (L) vs. 2.1 +/- 0.3% (F)], hemoglobin [13.5 +/- 0.3 (L) vs. 13.7 +/- 0.3 g/100 ml (F)], percent hematocrit [40.6 +/- 1.4 (L) vs. 40.7 +/- 1.0% (F)], red cell volume [31.1 +/- 3.6 (L) vs. 33.0 +/- 1.6 ml/kg (F)], and blood ferritin [8.9 +/- 1.7 (L) vs. 10.2 +/- 0.9 microg/l (F)]. Blood level of erythropoietin was related (r = 0.77) to arterial oxygen saturation but not to the levels of progesterone or estradiol. We conclude that erythropoiesis was not altered by menstrual cycle phase during the first days at 4,300-m altitude.

Chronic mountain sickness. A view from the crow's nest.

Chronic mountain sickness (CMS) is a poorly understood syndrome, characterized by hypoxemia and polycythemia and occurring in persons residing at high altitude. To better characterize the disorder, we have reviewed measurements in more than 750 men and 200 women living at altitude as published and as submitted by colleagues. In men, blood hemoglobin concentration (Hb) and arterial oxygen saturation (SaO2) related to altitude (r=0.72). There was greater variability in both SaO2 and hemoglobin above than below 3000 m, largely due to inter-individual variations in effective ventilation. For the entire cohort, a linear relationship (r=0.72) of an index of hematopoietic response (Hb) to an index of stimulus (SaO2) was independent of age, altitude, duration of altitude residence greater than one year, ethnic origin, geographic location, presence or absence of CMS and nearly independent of gender. A potentially important and usually unrecognized variation in the hypoxic stimulus was desaturation during sleep. Contributions to variation in response include ingested toxins, such as cobalt, and nutritional deficiencies, including iron. Pulmonary hypertension was related to chronic hypoxia, with an uncertain contribution from polycythemia. In CMS there were profound hypoxemia at night, decrease in cerebral blood flow, and loss of cerebral blood flow regulation, possibly causing the cerebral symptoms. We speculate that the relationship of Hb to SaO2 is more useful than of hemoglobin to altitude, that hypoventilation awake and asleep are the primary causes accentuating altitude-hypoxia, and that the brain is the primary target organ in the disorder.

Myocyte cytoskeletal disorganization and right heart failure in hypoxia-induced neonatal pulmonary hypertension.

Previous studies have demonstrated that environmentally or genetically induced changes in the intracellular proteins that compose the cytoskeleton can contribute to heart failure. Because neonatal right ventricular myocytes are immature and are in the process of significant cytoskeletal change, we hypothesized that they may be particularly susceptible to pressure stress. Newborn calves exposed to hypobaric hypoxia (barometric pressure = 430 mmHg) for 14 days developed severe pulmonary hypertension (pulmonary arterial pressure = 101 +/- 6 vs. 27 +/- 1 mmHg) and right heart failure compared with age-matched controls. Light microscopy showed partial loss of myocardial striations in the failing neonatal right but not left ventricles and in neither ventricle of adolescent cattle dying of altitude-induced right heart failure. In neonatal calves, immunohistochemical analysis of the cytoskeletal proteins (vinculin, metavinculin, desmin, vimentin, and cadherin) showed selectively, within the failing right ventricles, patchy areas characterized by loss and disorganization of costameres and intercalated discs. Within myocytes from the failing ventricles, vinculin and desmin were observed to redistribute diffusely within the cytosol, metavinculin appeared in disorganized clumps, and vimentin immunoreactivity was markedly decreased. Western blot analysis of the failing right ventricular myocardium showed, compared with control, vinculin and desmin to be little changed in total content but redistributed from insoluble (structural) to soluble (cytosolic) fractions; metavinculin total content was markedly decreased, tubulin content increased, particularly in the structural fraction, and cadherin total content and distribution were unchanged. We conclude that hypoxic pulmonary hypertensive-induced neonatal right ventricular failure is associated with disorganization of the cytoskeletal architecture.

Poor relationship between arterial [lactate] and leg net release during exercise at 4,300 m altitude.

We evaluated the hypotheses that on acute exposure to hypobaric hypoxia, sympathetic stimulation leads to augmented muscle lactate production and circulating [lactate] through a beta-adrenergic mechanism and that beta-adrenergic adaptation to chronic hypoxia is responsible for the blunted exercise lactate response after acclimatization to altitude. Five control and 6 beta-blocked men were studied during rest and exercise at sea level (SL), on acute exposure to 4,300 m (A1), and after a 3-wk sojourn at altitude (A2). Exercise was by leg cycling at 49% of SL peak O2 consumption (VO2 peak) (65% of altitude VO2 peak or 87 +/- 2.6 W); beta-blockade was by propranolol (80 mg 3x daily), femoral arterial and venous blood was sampled; leg blood flow (Q) was measured by thermodilution, leg lactate net release [ = (2) (1-leg Q) venous-arterial concentrationL] was calculated, and vastus lateralis needle biopsies were obtained. Muscle [lactate] increased with exercise and acute altitude exposure but regressed to SL values with acclimatization; beta-blockade had no effect on muscle [lactate]. Arterial [lactate] rose during exercise at SL (0.9 +/- 0.1 to 1.5 +/- 0.3 mM); exercise at A1 produced the greatest arterial [lactate] (4.4 +/- 0.8 mM), and exercise at A2 an intermediate response (2.1 +/- 0.6 mM). beta-Blockade reduced circulating [lactate] approximately 45% during exercise under all altitude conditions. increased transiently at exercise onset but then declined over time under all conditions. Blood and muscle "lactate paradoxes" occurred independent of beta-adrenergic influences, and the hypotheses relating the blood lactate response at altitude to beta-adrenergic mechanisms are rejected. During exercise at altitude, arterial [lactate] is determined by factors in addition to hypoxemia, circulating epinephrine, and net lactate release from active muscle beds.

Lung endothelial cell proliferation in normal and pulmonary hypertensive neonatal calves.

Tremendous changes in pressure and flow occur in the pulmonary and systemic circulations after birth, and these hemodynamic changes should markedly affect endothelial cell replication. However, in vivo endothelial replication rates in the neonatal period have not been reported. To label replicating endothelial cells, we administered the thymidine analog bromodeoxyuridine to calves approximately 1, 4, 7, 10, and 14 days old before they were killed. Because we expected the ratio of replicating to nonreplicating cells to vary with vascular segment, we examined the main pulmonary artery, a large elastic artery, three sizes of intrapulmonary arteries, the aorta, and the carotid artery. In normoxia for arteries < 1,500 micron, approximately 27% of the endothelial cells were labeled on day 1 but only approximately 2% on day 14. In the main pulmonary artery, only approximately 4% of the endothelial cells were labeled on day 1 and approximately 2% on day 14. In contrast, in the aorta, approximately 12% of the endothelial cells were labeled on day 1 and approximately 2% on day 14. In chronically hypoxic animals, only approximately 14% of the endothelial cells were labeled on day 1 in small lung arteries and approximately 8% were still labeled on day 14. We conclude that the postnatal circulatory adaptation to extrauterine life includes significant changes in endothelial cell proliferation that vary dramatically with time and vascular location and that these changes are altered in chronic hypoxia.

O2 extraction maintains O2 uptake during submaximal exercise with beta-adrenergic blockade at 4,300 m.

Whole body O2 uptake (VO2) during maximal and submaximal exercise has been shown to be preserved in the setting of beta-adrenergic blockade at high altitude, despite marked reductions in heart rate during exercise. An increase in stroke volume at high altitude has been suggested as the mechanism that preserves systemic O2 delivery (blood flow x arterial O2 content) and thereby maintains VO2 at sea-level values. To test this hypothesis, we studied the effects of nonselective beta-adrenergic blockade on submaximal exercise performance in 11 normal men (26 +/- 1 yr) at sea level and on arrival and after 21 days at 4,300 m. Six subjects received propranolol (240 mg/day), and five subjects received placebo. At sea level, during submaximal exercise, cardiac output and O2 delivery were significantly lower in propranolol- than in placebo-treated subjects. Increases in stroke volume and O2 extraction were responsible for the maintenance of VO2. At 4,300 m, beta-adrenergic blockade had no significant effect on VO2, ventilation, alveolar PO2, and arterial blood gases during submaximal exercise. Despite increases in stroke volume, cardiac output and thereby O2 delivery were still reduced in propranolol-treated subjects compared with subjects treated with placebo. Further reductions in already low levels of mixed venous O2 saturation were responsible for the maintenance of VO2 on arrival and after 21 days at 4,300 m in propranolol-treated subjects. Despite similar workloads and VO2, propranolol-treated subjects exercised at greater perceived intensity than subjects given placebo at 4,300 m. The values for mixed venous O2 saturation during submaximal exercise in propranolol-treated subjects at 4,300 m approached those reported at simulated altitudes >8,000 m. Thus beta-adrenergic blockade at 4,300 m results in significant reduction in O2 delivery during submaximal exercise due to incomplete compensation by stroke volume for the reduction in exercise heart rate. Total body VO2 is maintained at a constant level by an interaction between mixed venous O2 saturation, the arterial O2-carrying capacity, and hemodynamics during exercise with acute and chronic hypoxia.

Carl J. Wiggers and the pulmonary circulation: a young man in search of excellence.

Oddly, Carl Wiggers (1883-1962), who is remembered for his work on the systemic circulation, may be considered the "American father of the pulmonary circulation." In nearly-20 papers published in the American Journal of Physiology between 1909 and 1925, he reported the first reliable pressure contours in the pulmonary artery, inquired into the relationship between respiration and pulmonary arterial pressure, examined right atrial and right ventricular function, and demonstrated how right and left heart dynamics relate to heart sounds. He also stimulated direct visualization of the lung microcirculation. Method and concept are inextricably linked in the progress of science. His contributions to the pulmonary circulation were based on his high-fidelity pressure and sound recording instruments, which he ultimately applied in the left heart. Wiggers' search for excellence in method brought him well-deserved fame in the systemic circulation, but the search began in the lung.

Viral respiratory infection increases susceptibility of young rats to hypoxia-induced pulmonary edema.

Recent clinical observations of a high incidence of preexisting respiratory infections in pediatric cases of high-altitude pulmonary edema prompted us to ask whether such infections would increase the susceptibility to hypoxia-induced pulmonary edema in young rats. We infected weanling rats with Sendai virus, thus causing a mild respiratory infection. Within 7 days of infection, Sendai virus was essentially undetectable by using viral culture and immunohistochemical techniques. Animals at day 7 of Sendai virus infection were then exposed to normobaric hypoxia (fraction of inspired O2 = 0.1) for 24 h and examined for increases in gravimetric lung water and in vascular permeability, as well as for histological evidence of increased lung water. Bronchoalveolar lavage was performed on a separate series of animals. Compared with control groups, infected hypoxic animals showed significant increases in perivascular cuffing, gravimetric lung water, and lung protein leak. In addition, infected hypoxic animals had increases in lavage fluid cell counts and protein content compared with controls. We conclude that young rats, exposed to moderate hypoxia while recovering from a mild viral respiratory infection, may demonstrate evidence of early pulmonary edema formation, a finding of potential relevance to human high-altitude pulmonary edema.

Beta-adrenergic blockade does not prevent polycythemia or decrease in plasma volume in men at 4300 m altitude.

When humans ascend to high altitude (ALT) their plasma volume (PV) and total blood volume (BV) decrease during the first few days. With continued residence over several weeks, the hypoxia-induced stimulation of erythropoietin increases red cell production which tends to restore BV. Because hypoxia also activates the beta-adrenergic system, which stimulates red blood cell production, we investigated the effect of adrenergic beta-receptor inhibition with propranolol on fluid volumes and the polycythemic response in 11 healthy unacclimatized men (21-33 years old exposed to an ALT of 4300 m (barometric pressure 460 Torr) for 3 weeks on Pikes Peak, Colorado. PV was determined by the Evans blue dye method (PVEB), BV by the carbon monoxide method (BVCO), red cell volume (RCV) was calculated from hematocrit (Hct) and BVCO, and serum erythropoietin concentration ([EPO]) and reticulocyte count, were also determined. All determinations were made at sea level and after 9-11 (ALT-10) and 19-20 (ALT-20) days at ALT. At sea level and ALT, six men received propranolol (pro, 240 mg x day[-1]), and five received a placebo (pla). Effective beta-blockade did not modify the mean (SE) maximal values of [EPO] [pla: 24.9 (3.5) vs pro: 24.5 (1.5) mU x ml(-1)] or reticulocyte count [pla: 2.7 (0.7) vs pro: 2.2 (0.5)%]; nor changes in PVEB [pla: -15.8 (3.8) vs pro: -19.9 (2.8)%], RCVCO [pla: +7.0 (6.7) vs pro: + 10.1 (6.1)%], or BVCO [pla: -7.3 (2.3) vs pro: -7.1 (3.9)%]. In the absence of weight loss, a redistribution of body water with no net loss is implied. Hence, activation of the beta-adrenergic system did not appear to affect the hypovolemic or polycythemic responses that occurred during 3 weeks at 4300 m ALT in these subjects.

Inflammatory processes may predispose children to high-altitude pulmonary edema.

We investigated retrospectively whether the preexistence of inflammation-producing illnesses such as viral respiratory tract infections contributed to the development of high-attitude pulmonary edema in children. We found that the large majority of native low-attitude children, but not adults, who had this form of edema after traveling to high altitude also had evidence of a preexisting illness. We speculate that the release of inflammatory mediators associated with these illnesses may be tolerated at sea level but may predispose children to increased capillary permeability when superimposed on hypoxia and, possibly, cold and exercise.

Relation of sympathetic activation to ventilation in man at 4300 m altitude.

BACKGROUND: The sympathetic nervous activity increases at high altitude but is not maximal initially when hypoxemia is most severe. HYPOTHESIS: The sympathetic activation would correlate better to the ventilatory response to chronic hypoxia than to the severity of hypoxia per se. METHODS: Eleven healthy male volunteers (27 +/- 1 yr) had measurements from the abdominal aorta of pressure, catecholamines, and blood gases at sea level, on arrival at 4300 m, and after 21 d of residence. Additionally, we measured 24-h urinary catecholamine excretion at sea level and each day at altitude, and made serial measurements of resting ventilatory parameters. RESULTS: Arterial norepinephrine (NE) concentrations on arrival at 4300 m were little changed from sea level, but were increased following acclimatization at 21 d. Arterial oxygenation was decreased on arrival, but improved with acclimatization. Arterial epinephrine (E) concentrations were increased on arrival, and returned to an intermediate level by 21 d. The urinary NE excretion was increased along with the increase in VE (p < 0.01) and the fall in end-tidal PCO2 (p < 0.001), but not with the decrease in end-tidal PO2 during the sojourn at 4300 m. Excretion of E did not relate to any ventilatory parameters. Propranolol (240 mg.d-1), which was given to 6 of 11 subjects, did not affect any relationships. CONCLUSION: The sympathetic activation was related to the ventilatory response but not to measures of hypoxemia at 4300 m. We conclude that factors related to ventilatory acclimatization, possibly increased chemoreceptor activity, contribute to the development of sympathetic activation at high-altitude.

Acclimatization to 4,300-m altitude decreases reliance on fat as a substrate.

We tested the hypothesis that exposure to altitude decreases reliance on free fatty acids (FFA) as substrates and increases dependency on blood glucose. Therefore, the effects of exercise, hypobaric hypoxia, and altitude acclimatization on FFA, glycerol and net glucose uptake and release [= 2(leg blood flow)(arteriovenous concentration)] and on fatty acid (FA) consumption by the legs (= 3 x glycerol release + FFA uptake) were measured. Because sympathetic responses have been implicated, we utilized nonspecific beta-blockade and observed responses to exercise, altitude, and altitude acclimatization. We studied six healthy beta-blocked men (beta) and five matched controls (C) during rest and cycle ergometry exercise (88 W) at 49% of sea-level (SL) peak O2 uptake at the same absolute power output on acute altitude exposure (A1; barometric pressure = 430 Torr) and after 3 wk of chronic altitude exposure to 4,300 m (A2). During exercise at SL, FA consumption rates increased (P < 0.05). On arrival at 4,300 m, resting leg FFA uptake and FA consumption rates were not significantly different from those at SL. However, after acclimatization to altitude, at rest leg FA consumption decreased to essentially zero in both C and beta groups. During exercise to altitude after acclimatization, leg FA consumption increased significantly, but values were less than at SL or A1 (P < 0.05), whereas glucose uptake increased relative to SL values. Furthermore, beta-blockade significantly increased glucose uptake relative to control. We conclude that 1) chronic altitude exposure decreases leg FA consumption during rest and exercise; 2) relative to SL FFA uptake decreases while glucose uptake increases during exercise at altitude; and 3) beta-blockade potentiates these effects.

Treatment of high-altitude pulmonary edema by bed rest and supplemental oxygen.

STUDY OBJECTIVES: We evaluated the safety and efficacy of treating high-altitude pulmonary edema (HAPE) by bed rest and supplemental oxygen at moderate altitudes. We also characterized clinical parameters in HAPE before and after treatment. DESIGN: Case series. SETTING: Two primary care centers at about 9,200 feet (2,800 meters) above sea level. TYPE OF PARTICIPANTS: All patients aged 16-69 years who had been diagnosed with HAPE and were treated with bed rest and supplemental oxygen. Patients were seen on a follow-up visit. INTERVENTIONS: Selected patients were treated with bed rest and supplemental oxygen rather than hospital admission or descent. MAIN OUTCOME MEASURE: Patients were considered improved on follow-up if room air arterial oxygen saturation was increased by 10 percentage points or if their symptoms had improved. RESULTS: Of 58 patients with confirmed HAPE, 25 (43%) were treated by bed rest and supplemental oxygen and were seen on return visits to the clinic. All of the treated patients improved at the return visit. Systolic blood pressure, heart rate, respiratory rate, and temperature decreased significantly between the first visit and the return visit. Oxygen saturation improved between visits. CONCLUSION: Some patients with HAPE at moderate altitudes where medical facilities are available can be safely treated with bed rest and oxygen without descent.