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PubMed1997

Ins(1,4,5)P3 receptors in cerebral arteries: changes with development and high-altitude hypoxia.

We and others have shown that adrenergic-mediated contractile responses in cerebral vessels in vitro differ with vessel segment, with developmental age, and with high-altitude, long-term hypoxia. This is associated with significant differences in alpha 1-adrenergic receptor density and norepinephrine (NE)-induced response of the second messenger inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]. To test the hypothesis that vessel-specific, developmental, and hypoxic-associated contractility changes are mediated, in part, by changes in Ins(1,4,5)P3-receptor [Ins(1,4,5)P3-R] density or affinity, we performed the following study. In common carotid (Com), circle of Willis, and main branch anterior, middle, and posterior cerebral arteries (MBC) from normoxic fetal (approximately 140 days), newborn (3-5 days), and adult sheep and fetal and adult sheep acclimatized to high altitude, we quantified Ins(1,4,5)P3-R with [3H]Ins(1,4,5)P3. In normoxic Com, Ins(1,4,5)P3-R density values (fmol/mg protein) in fetus, newborn, and adult were 8 +/- 53, 150 +/- 18, and 357 +/- 21, respectively (P < 0.05). In normoxic MBC cerebral arteries, the receptor density values in the three age groups were 115 +/- 15, 105 +/- 9, 99 +/- 5 fmol/mg protein, respectively. For fetal and adult Com, high-altitude, long-term hypoxemia was associated with decreases in Ins(1,4,5)P3-R density of 32 (to 58 +/- 5) and 70% (to 109 +/- 12), respectively, from control values (P < 0.01). In MBC cerebral arteries of fetus and adult, hypoxic-associated decreases in Ins(1,4,5)P3-R density from control were 80 (to 23 +/- 3) and 47% (to 53 +/- 7), respectively (P < 0.01). Ins(1,4,5)P3 binding affinity to the receptor averaged 11.8 +/- 0.5 nM and did not vary significantly as a function of vessel type, developmental age, or hypoxia. In Com, but not in MBC, Ins(1,4,5)P3-R density increased dramatically with developmental age. This suggests that differences in Ins(1,4,5)P3-R density values may account, in part, for differences in contractile responses of the two artery types in the several age groups. In response to long-term, high-altitude hypoxia, Ins(1,4,5)P3-R density values in both fetal and adult Com and MBC decreased significantly, as did their NE-induced contraction. This suggests a cellular basis for changes in cerebrovascular contractility in response to long-term hypoxia and that Ins(1,4,5)P3-R may play a role in acclimatization responses to high altitude.

Aging↗

PubMed1998

Effects of maturation, artery size, and chronic hypoxia on 5-HT receptor type in ovine cranial arteries.

To test the hypothesis that variations in cerebrovascular reactivity to 5-HT among arteries of different size or type, during maturation, or during acclimatization to high altitude involve differences in serotonergic receptor subtype, we determined relative agonist potency orders and antagonist affinities in common carotid (Com), main branch middle cerebral (Main), and second branch middle cerebral (2BR) arteries from term fetal lambs and nonpregnant adult sheep acclimatized at sea level or at an altitude of 3,820 m for approximately 110 days. In normoxic adult Com segments, agonist potency order was 5-hydroxytryptamine (5-HT) > 5-carboxamidotryptamine (5-CT) >/= 8-hydroxy-2(di-n-propylamino)tetraline (8-OH-DPAT); sumatriptan (Suma) produced no contractile response; and antagonist dissociation constant (pKb) values were 9.4 and 9.5 for ketanserin against 5-HT and 5-CT, 7.5 for GR-127935 against 5-HT, and 7.2 for SB-206553 against 5-HT. In normoxic adult Main segments, agonist potency order was 5-HT > 5-CT >/= Suma >/= DPAT, and pKb values were 9.1 and 9.2 for ketanserin against 5-HT and 5-CT and 7.4 and 8.5 for GR-127935 against 5-HT and Suma, respectively. In the 2BR segments from normoxic adults, agonist potency order was 5-CT > 5-HT > Suma > DPAT and pKb values were 7.4 and 7.2 for ketanserin against 5-HT and 5-CT and 10.0 and 8.7 for GR-127935 against 5-HT and Suma, respectively. Compared with normoxic adults, none of these values were significantly different in hypoxic adults and in fetuses only the pKb values for ketanserin against 5-HT in the 2BR segments (8.8) were greater. From these results we propose that the ratio of 5-HT2 to 5-HT1 receptors is greatest in the Com and decreases progressively to its smallest values in 2BR or smaller segments. Because this gradient appears stable and relatively resistant to the effects of maturation and chronic hypoxia, changes in reactivity associated with these perturbations may involve alterations in receptor density and/or coupling efficiency for 5-HT in ovine cranial arteries.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1975

Effects of moderate hypoxemia and hypocapnia on CSF [H+] and ventilation in man.

The effects of 26 h of normoxic hypocapnia (PaCO2, 31 MMHg) vs. 26 h of hypocapnia plus hypobaric hypoxia (PaCO2 32, PaO2 57 mmHg) were compared with respect to: a) CSF acid-base status; and b) the spontaneous ventilation (at PIO2 145 mmHg) which followed the imposed (voluntary) hyperventilation. For each condition of prolonged hypocapnia, PaCO2 was held constant throughout and pHa and [HCO3-]a were constant over the final 6-10 h. We assumed that measured changes in lumbar CSF acid-base status paralleled those in cisternal CSF. Spontaneous hyperventilation followed both normoxic and hypoxic hypocapnia but was significantly greater following hypoxic hypocapnia. In the CSF, pH compensation after 26 h of hyperventilation was incomplete (similar to 45-50%), was similar to that in arterial blood, and was unaffected by a superimposed hypoxemia. These data were inconsistent with current theory which proposes the regulation of CSF [HCO2] via local mechanisms and, in turn, the mediation of ventilatory acclimatization to hypoxemia and/or hypocapnia via CSF [H+]. Alternative mediators of ventilatory acclimatization were postulated, including mechanisms both dependent on and independent of "chemoreceptor" stimuli.

Acid-Base Equilibrium↗

PubMed1979

Oxygen affinity of blood in altitude Sherpas.

Oxygen equilibrium curves on blood within 6 h from sampling have been estimated from polarographic measurements of oxyhemoglobin concentration, in 13 male 14- to 50-yr old Sherpas residing at 3,850 m above sea level (Kumjung, Nepal). In samples with red blood cell counts = 4.7 +/- 0.8 (SD) x 10(6)/mm3, total hemoglobin concentration [Hb] = 17.0 +/- 1.9 g/dl, and hematocrit = 53.3 +/- 5.0, the mean oxygen half-saturation of hemoglobin (P50) (pH = 7.4 and PCO2 = 40 Torr) was 27.3 +/- 1.8 Torr. The P50 of altitude Sherpas was not significantly different from that of acclimatized lowlanders (28.2 +/- 1.3; n = 7), sea-level Caucasian residents (26.5 +/- 1.0; n = 17), and Sherpas at sea level (27.1; n = 3). The 2,3-diphosphoglyceric acid-to-hemoglobin concentration ratio ([2,3-DPG]/[Hb]) in altitude Sherpas was 1.22 +/- 0.03, the same as that of acclimatized Caucasians (1.22 +/- 0.10). The Bohr effect measured for the blood of one altitude Sherpas by the ratio deltalog P50/deltapH was -0.32 and -0.45 at PCO2 levels of 40 and 20 Torr, respectively. These values are not significantly different from those found in Caucasians at sea level where deltalog P50/deltalpH was -0.35 and -0.42, respectively. It is concluded that the P50 in native highlanders is not significantly different from that observed in sea-level dwellers. [2,3-DPG]/[Hb] at altitude, both in natives and in newcomers, is 20% higher than in sea-level residents.

Adaptation, Physiological↗

PubMed1981

Effects of hypoxia on density of beta-adrenergic receptors.

Exposure to chronic hypoxia results in a lower resting heart rate and a blunted cardiovascular responsiveness to beta-adrenergic receptor stimulation. Possible effects of acclimatization to high altitude on the binding of [125I]iodohydroxybenzylpindolol to beta-adrenergic receptors on membranes of right and left ventricles of rat heart were determined. Chronic high-altitude exposure led to a decrease in the density of beta-adrenergic receptors in nonhypertrophied left ventricles as well as in hypertrophied right ventricles. The affinity of the receptor for the radioligand was not changed by the exposure to high altitude, suggesting that the properties of the receptor were not affected. Basal and isoproterenol-stimulated adenylate cyclase activities were decreased in membranes prepared from hearts and pulmonary arteries of rats acclimatized to high altitude. The loss of cardiac beta-adrenergic receptors in rats adapted to high altitude was prevented by the chronic coadministration of a low dose of DL-propranolol. The results suggest that changes in beta-adrenergic receptor density may partially explain the hemodynamic adaptation that occurs with chronic hypoxia. These decreases may be due to a loss of functional beta-adrenergic receptors caused by chronically elevated concentrations of circulating neurally released catecholamines.

Adenylyl Cyclases↗

PubMed1983

Cardiorespiratory response to exercise in men repeatedly exposed to extreme altitude.

The ventilatory and heart rate responses to exercise were studied in four experienced high-altitude climbers at sea level and during a 6-wk period above 4,500 m to discover whether their responses to hypoxia were similar to those of high-altitude natives. Comparison was made with results from four scientists who lacked their frequent exposure to extreme altitude. The climbers had greater Vo2max at sea level and altitude but similar ventilatory responses to increasing exercise. On acute hypoxia at sea level their ventilatory response was less than that of scientists. Their heart rate response did not differ from that of scientists at sea level, but with acclimatization the reduction in response was significantly greater. Alveolar gas concentrations were similar after acclimatization, but climbers achieved these changes more rapidly. The increase in hematocrit was similar in the two groups. It is concluded that these climbers, unlike high-altitude residents, have cardiorespiratory responses to exercise similar to those of other lowlanders except that their ventilatory response was lower and the reduction in their heart rate response was greater.

Adult↗

PubMed1988

Carotid body excision significantly changes ventilatory control in awake rats.

We determined the effects of carotid body excision (CBX) on eupneic ventilation and the ventilatory responses to acute hypoxia, hyperoxia, and chronic hypoxia in unanesthetized rats. Arterial PCO2 (PaCO2) and calculated minute alveolar ventilation to minute metabolic CO2 production (VA/VCO2) ratio were used to determine the ventilatory responses. The effects of CBX and sham operation were compared with intact controls (PaCO2 = 40.0 +/- 0.1 Torr, mean +/- 95% confidence limits, and VA/VCO2 = 21.6 +/- 0.1). CBX rats showed 1) chronic hypoventilation with respiratory acidosis, which was maintained for at least 75 days after surgery (PaCO2 = 48.4 +/- 1.1 Torr and VA/VCO2 = 17.9 +/- 0.4), 2) hyperventilation in response to acute hyperoxia vs. hypoventilation in intact rats, 3) an attenuated increase in VA/VCO2 in acute hypoxemia (arterial PO2 approximately equal to 49 Torr), which was 31% of the 8.7 +/- 0.3 increase in VA/VCO2 observed in control rats, 4) no ventilatory acclimatization between 1 and 24 h hypoxia, whereas intact rats had a further 7.5 +/- 1.5 increase in VA/VCO2, 5) a decreased PaCO2 upon acute restoration of normoxia after 24 h hypoxia in contrast to an increased PaCO2 in controls. We conclude that in rats carotid body chemoreceptors are essential to maintain normal eupneic ventilation and to the process of ventilatory acclimatization to chronic hypoxia.

Acute Disease↗

PubMed1993

Autonomic regulation of heart rate response to exercise in Tibetan and Han residents of Lhasa (3,658 m).

To test the hypothesis that native high-altitude residents have less beta-sympathetic and more parasympathetic tone than newcomers, we compared the effects of beta-sympathetic and parasympathetic blockade in 10 Tibetan and 9 Han acclimatized male residents of Lhasa, Tibet Autonomous Region, China (elevation 3,658 m). Each subject was studied during cycle ergometer exercise at 70, 132, and 191 W after placebo (normal saline), beta-sympathetic (propranolol, 0.2 mg/kg iv), or parasympathetic (atropine, 0.04 mg/kg iv) blockade in random order on different days. At rest, the fall in resting heart rate with propranolol and the rise with atropine were equal in Tibetan and Han subjects. During exercise, the fall in heart rate with propranolol relative to placebo values was greater in the Han than in the Tibetan group, whereas the rise in heart rate with atropine was greater in the Tibetans. Propranolol or atropine administration did not change minute ventilation per unit O2 consumption in either group. At the highest level of exercise on the placebo day, the Tibetans achieved a higher work load and level of O2 consumption than the Han subjects. Propranolol or atropine reduced O2 consumption and work load similarly in the two groups at the highest exercise level. The results supported our hypothesis that native Tibetan residents of high altitude exhibit more para-sympathetic and less beta-sympathetic tone during exercise. Neither relatively greater parasympathetic nor less sympathetic activation appeared implicated in the greater exercise capacity of Tibetans compared with that of acclimatized newcomer residents of high altitude.

Adult↗

PubMed1996

Augmented hypoxic cerebral vasodilation in men during 5 days at 3,810 m altitude.

The fractional increase in cerebral blood flow (CBF) velocity (VCBF) from the control value with 5-min steps of isocapnic hypoxia and hyperoxic hypercapnia was measured by transcranial Doppler in six sea-level native men before and during a 5-day sojourn at 3,810 m altitude to determine whether cerebral vasoreactivity to low arterial O2 saturation (SaO2) gradually increased [as does the hypoxic ventilatory response (HVR)] or diminished (adapted, in concert with known slow fall of CBF) at altitude. A control resting PCO2 value was chosen each day during preliminary hyperoxia to set ventilation at 140 ml.kg-1.min-1 for this and the parallel HVR study, attempting to establish control cerebrospinal fluid (CSF) and brain extracellular fluid pH values unaltered by acclimatization. The relationship of CBF to SaO2 was nonlinear, steepening at a lower SaO2. A hyperbolic equation was used to describe hypoxic cerebrovascular reactivity: fractional VCBF = x[60/ (SaO2-40)-1], where X is the fractional increase of VCBF at 70%.X rose from 0.346 +/- 0.104 (SD) at sea level to 0.463 +/- 0.084 on altitude day 5 (P < 0.05 by paired t-test, justified by the a priori experimental plan). For comparison with CO2 sensitivity, from these X values, we estimate the rise in CBF in response to a 1% fall in SaO2 at 80% to be 1.30% at sea level and 1.74% after 5 days at altitude. CBF sensitivity to increased end-tidal PCO2 rose from 4.01 +/- 0.62%/Torr at sea level to 5.12 +/- 0.79%/Torr on day 5 (P < 0.05), as expected, at the lower PCO2 due to the logarithmic relationship of PCO2 to CSF pH. This change was not significant after correction to log PCO2. We conclude that the cerebral vascular response to acute isocapnic hypoxia may increase during acclimatization at high altitude. The mechanism is unknown but is presumably unrelated to the parallel carotid chemosensitization that, in these subjects, increased the HVR by 60% in the same 5-day period from 0.91 +/- 0.38 to 1.46 +/- 0.59 l.min-1.% fall in SaO2-1).

Adult↗

PubMed2001

Alterations in enzymes involved in fat metabolism after acute and chronic altitude exposure.

The purpose of this study was to examine the effect of acute (24 h) and chronic (5 wk) hypobaric hypoxic exposure equivalent to a simulated altitude of 4,300 m (446 mmHg) on the enzymes of fat metabolism. Heart, liver, and skeletal muscle were taken from 32 male Sprague-Dawley rats. Altitude exposure did not affect the activity of citrate synthase in any of the tissues, suggesting that mitochondrial content was unchanged. Carnitine palmitoyltransferase-I (CPT-I) activity was significantly reduced in the heart by both acute and chronic high altitude exposure compared with controls. A similar reduction was found for CPT-I activity in extensor digitorum longus after acute and chronic exposure compared with control animals. CPT-I activity was not affected by altitude exposure in the soleus muscle or the liver. 3-Hydroxyacyl-CoA dehydrogenase (beta-HAD) activity was significantly depressed in the hearts of chronically exposed animals compared with controls. No difference between acute and control animals was found in the heart for beta-HAD activity. Liver beta-HAD activity was also significantly decreased in the acclimatized as well as in the acute animals compared with the control group. Quadriceps beta-HAD activity was reduced for the chronic animals only compared with controls. These data suggest that acclimatization to high altitude selectively decreases key enzymes in fat utilization and oxidation in the heart, liver, and select skeletal muscles.

3-Hydroxyacyl CoA Dehydrogenases↗

PubMed2001

Exercise training alters the effect of chronic hypoxia on myocardial adrenergic and muscarinic receptor number.

Chronic hypoxic exposure results in elevated sympathetic activity leading to downregulation of myocardial alpha(1)- and beta-adrenoceptors (alpha(1)-AR, beta-AR). On the other hand, it has been shown that sympathetic activity is reduced by exercise training. The objective of this study was to determine whether exercise training could modify the changes in receptor expression associated with acclimatization. Four groups of rats were studied: normoxic sedentary rats (NS), rats living and training in normoxia (NTN), sedentary rats living in hypoxia (HS, inspired PO(2) = 110 Torr), and rats living and training in hypoxia (HTH, inspired PO(2) = 110 Torr). Training consisted of running in a treadmill at 80% of maximal O(2) uptake during 10 wk. Myocardial receptor density was measured by radioactive ligand binding. Right ventricular (RV) hypertrophy occurred in HS but not in HTH. No effect of exercise was detected in RV weight of normoxic rats. Acclimatization to hypoxia (HS vs. NS) resulted in a decrease in both alpha(1)- and beta-AR density, whereas muscarinic receptor (M-Ach) expression increased. Hypoxic exercise training (HS vs. HTH) moderated beta-AR downregulation and M-Ach upregulation and prevented the fall in alpha(1)-AR density. Normoxic training (NS vs. NTN) did not change beta-AR density. On the other hand, densities of alpha(1)-AR in both ventricles as well as RV M-Ach increased in NTN vs. NS. The data show that exercise training in hypoxia 1) prevents RV hypertrophy, 2) suppresses the downregulation of alpha(1)-AR in the left ventricle (LV) and RV, and 3) attenuates the changes in both beta-AR and M-Ach receptor density in LV and RV. Exercise training in normoxia increases M-Ach receptor expression in the RV.

Animals↗

PubMed1978

On the role of the pineal in thermoregulation in the pigeon.

Diurnal rhythm in body temperature of pigeons subjected to different experimental conditions (pinealectomized, sham-operated, melatonin-implanted, cold-exposed) was studied under a 12 h light and 12 h dark regimen. The body temperature of pigeons during photophase was higher than that during scotophase in the normal as well as every treatment group studied. Pinealectomized pigeons showed higher body temperature in the photophase as well as scotophase, than that of the normal and sham-operated birds when examined 2 or 3 weeks following the post-surgical acclimatization to 25 or 3 degrees C. However, subcutaneous implantation of melatonin pellets into pinealectomized pigeons nullified or even reversed the hyperthermic effect of pinealectomy. Exposure of pigeons to--18 degrees C for 280 min during photophase as well as scotophase, produced a marked drop in body temperature in pinealectomized, sham-operated and normal pigeons. The pinealectomized pigeons exhibited a higher body temperature than that of the sham-operated and normal ones when exposed to--18 degrees C during the photophase, but not during the scotophase. It was concluded that while the pineal is not necessary for maintaining the daily thermal rhythm in the avian body, it has a thermoregulatory role, in that it prevents rise in body temperature in warm (25 degrees C) acclimatized and chronic cold (3 degrees C) exposed birds. In acute short-term cold (--18 degrees C) exposure however, the temperature regulatory role of the pineal was not effective during the scotophase.

Animals↗

PubMed1997

Respiratory function at different altitudes.

For the evaluation of a respiratory test at high altitude, several factors must be taken into account: the decreased barometric pressure, the decreased density of air and the degree of acclimatization which is related to the altitude and to the length of exposure. Several studies have shown a reduction in forced vital capacity (FVC) at high altitude and using simulated conditions, mainly related to an increase in pulmonary blood volume and development of interstitial edema. To assess the daily spirometric patterns during ascending to high altitudes we studied 17 healthy subjects at both Capanna Regina Margherita on the Italian Alps (4,559 m) and the Pyramid Laboratory in Nepal (5,050 m). Respiratory function tests were performed every day. Peak expiratory flow values significantly increased. The mean percent increase was 15% at 3,200 and 3,600 m and 26% at 4,559 m. FVC and MEF25 values showed a significant decrease (p < 0.005) during the first days above 3,500 m and improved only after several days spent above this altitude. For each subject the maximal reductions in FVC and maximal expiratory flow (MEF) at 25% of FVC however were found on different days. In our opinion, these data support the hypothesis that at high altitude the respiratory function can be affected by the presence of an increased pulmonary blood volume and/or the development of interstitial edema. The observed changes in forced expiration curves at high altitude seem to reflect the degree of acclimatization that is related to the individual susceptibility, to the altitude reached and to the duration of the exposure. These changes are transient and resolve after returning to sea level.

Adult↗

PubMedDate not supplied

Protein metabolism in rats during long-term dietary restriction: influence of aging.

BACKGROUND: Protein depletion is frequent in the elderly, but the underlying mechanisms are not yet fully understood. In particular, it is unknown whether there is a defect of adaptation to a restriction of food intake in the elderly. This study was performed to compare the effects of 6-week dietary restriction (DR) on protein metabolism in both adult and aged rats. METHODS: Adult (3-month-old) and aged (22-month-old) rats were acclimatized for 2 weeks and then fed a standard diet for 6 weeks, either ad libitum (control adult [C(Adult)] and aged [C(Aged)] rats) or with only 50% of the average intake of the second week of acclimatization (restricted adult [R(Adult)] and aged [R(Aged)] rats). Protein metabolism, in terms of tissue protein content, nitrogen balance, and 3-methylhistidine (3-MH) urinary excretion, was evaluated. RESULTS: C(Adult) rats gained 30.4% of initial weight, whereas the body weight (BW) of C(Aged) rats was maintained. DR induced a rapid decrease in BW during the first 2 weeks in R(Adult) rats, but afterward BW remained stable. In R(Aged) rats, BW loss was linear during the 6 weeks and significantly higher than for R(Adult) rats (p<.01). In both restricted groups, muscle protein content was moderately affected by DR, whereas DR induced a marked decrease in visceral protein content. Nitrogen balance was decreased by DR but stayed positive in R(Adult) rats, whereas it became null in R(Aged) rats. CONCLUSIONS: In terms of protein metabolism, aged rats adapted less efficiently than adult rats to a long-term dietary restriction.

Aging↗

PubMedDate not supplied

Mountaineering accidents in the Sierra Nevada.

Two hundred and fifteen mountaineering accidents occurred in the Sierra Nevada over a 5-year period in climbers on Class V routes. Patients were evaluated for: climbing preparation and training, first aid experience, altitude acclimatization, age, anatomical site of injuries, and cause of the injury. Consideration as to evacuation procedure was also given. The effect of high altitude exposure impairs judgment and muscular coordination and implies poor acclimatization. Acute mountain sickness and hypothermia were documented in 104 patients, the majority of whom sustained injuries resulting from judgmental errors. Ninety-four injuries involved the ankle and lower tibia, an incidence similar to that seen in alpine skiing a decade ago. There were 17 deaths resulting most frequently from head injuries. Few climbers had formal training in basic mountain medicine which was reflected in the poor assessment and management of injuries, with an unnecessary reliance upon others for evacuation. Morbidity and mortality may be lessened by proper climbing preparation--instruction in mountaineering techniques as well as basic mountain medicine--and by prevention of acute mountain sickness and cold injury.

Adolescent↗

PubMed2005

Differential freshwater adaptation in juvenile sea-bass Dicentrarchus labrax: involvement of gills and urinary system.

The effects of long-term freshwater acclimatization were investigated in juvenile sea-bass Dicentrarchus labrax to determine whether all sea-bass juveniles are able to live in freshwater and to investigate the physiological basis of a successful adaptation to freshwater. This study particularly focused on the ability of sea-bass to maintain their hydromineral balance in freshwater and on their ion (re)absorbing abilities through the gills and kidneys. Two different responses were recorded after a long-term freshwater acclimatization. (1) Successfully adapted sea-bass displayed standard behavior; their blood osmolality was maintained almost constant after the freshwater challenge, attesting to their efficient hyperosmoregulation. Their branchial and renal Na+/K+-ATPase abundance and activity were high compared to seawater fish due to a high number of branchial ionocytes and to the involvement of the urinary system in active ion reabsorption, producing hypotonic urine. (2) Sea-bass that had not successfully adapted to freshwater were recognized by abnormal schooling behavior. Their blood osmolality was low (30% lower than in the successfully adapted sea-bass), which is a sign of acute osmoregulatory failure. High branchial Na+/K+-ATPase abundance and activity compared to successfully adapted fish were coupled to a proliferation of gill chloride cells, whose ultrastructure did not display pathological signs. The large surface used by the gill chloride cells might negatively interfere with respiratory gas exchanges. In their urinary system, enzyme abundance and activity were low, in accordance with the observed lower density of the kidney tubules. Urine was isotonic to blood in unsuccessfully adapted fish, ruling out any participation of the kidney in hyperosmoregulation. The kidney failure seems to generate a compensatory ion absorption through increased gill activity, but net ion loss through urine seems higher than ion absorption by the gills, leading to lower hyper-osmoregulatory performance and to death.

Adaptation, Physiological↗

PubMed1996

Seasonal-, tidal-cycle- and microhabitat-related variation in membrane order of phospholipid vesicles from gills of the intertidal mussel Mytilus californianus

Alterations in the order, or fluidity, of cellular membranes in response to variations in environmental temperature are well known. The mussel Mytilus californianus, a common inhabitant of mid-intertidal regions along the Pacific coast of North America, can experience large (20 °C or more) and cyclic (every 6 h) changes in body temperature (Tb ) during tidal cycles. In the present study, we explore membrane order during seasonal and tidal temperature cycles and find that vesicles prepared from gill phospholipids exhibit significant seasonal differences in order that are consistent with homeoviscous adaptation and suggest winter-acclimatization to mean Tb values and summer-acclimatization to upper extreme Tb values or to large cyclic thermal fluctuations, despite repeated resubmergence in sea water at 10 °C during both seasons. Phospholipid vesicles prepared from the gills of mussels acclimated for 6 weeks to constant high or low temperatures in the laboratory fail to exhibit temperature-compensatory differences in order. In addition, during the summer, mussels inhabiting high intertidal sites, but not those from low sites, possess the ability to alter membrane order rapidly (within hours). This alteration of order appears to represent a mechanism designed to offset the thermal variations encountered during the tidal cycle. Thus, M. californianus have the ability to adjust membrane order on seasonal as well as hourly time scales and do so on the basis of their height in the intertidal region.

Journal Article↗

PubMed2003

Heat illness in children.

With an increasing number of children and adolescents involved in competitive athletics throughout the calendar year, the sports medicine team must be familiar with preventing and treating heat-related illness. Heat illness is a spectrum of illnesses from heat cramps to heat stroke. Mortality for heat stroke ranges from 17% to 70%, depending on severity and age of the patient. Children are more susceptible to heat illness than adults for many reasons, including a greater surface area to body mass ratio, lower rate of sweating, and slower rate of acclimatization. The prevention of heat illness is based on recognizing and modifying risk factors, which include environmental conditions, clothing, hydration, and acclimatization. Once heat illness is suspected, treatment should begin immediately with rapid cooling procedures started on the field.

Body Temperature Regulation↗