Physiological significance of behavioral hypothermia in hypoxic toads (Bufo marinus)

1991 ◽  
Vol 159 (1) ◽  
pp. 203-215 ◽  
Author(s):  
S. C. Wood ◽  
G. M. Malvin
Keyword(s):  
Behavioral Response ◽  
Thermal Gradient ◽  
Respiratory Exchange Ratio ◽  
Ventilatory Response ◽  
Respiratory Alkalosis ◽  
Significant Rise ◽  
Bufo Marinus ◽  
Significant Drop ◽  
Preferred Temperature ◽  
Beneficial Response

We tested the hypotheses that hypoxic toads (Bufo marinus) in a thermal gradient would select a lower than normal temperature and that this behavioral response would be beneficial. Under normoxic conditions, selected body temperature was 24.2 +/− 3.6 degrees C. When inspired O2 was 10% or less, mean selected temperature decreased to 15.3 +/− 2.4 degrees C. The theoretical advantages of hypoxia-induced hypothermia we tested include (1) a reduction of oxygen uptake (VO2) by a Q10 effect; (2) increased arterial saturation (SaO2), (3) a decreased ventilatory response, and (4) a decreased stress response. Gas exchange, hematocrit, hemoglobin, SaO2, PaO2 and pH were measured at 25 degrees C (normal preferred temperature) and 15 degrees C (hypoxia preferred temperature) in toads breathing normoxic or hypoxic gas mixtures. During graded hypoxia at 15 degrees C, SaO2 was significantly increased and VO2 was significantly reduced compared with 25 degrees C. Graded hypoxia did not significantly affect VO2 at 25 degrees C, despite evidence for increased ventilation at that temperature (increased pH and respiratory exchange ratio, RE). At 15 degrees C, graded hypoxia had a significant effect on VO2 only at an inspired O2 of 4%. Increased RE with hypoxia was significant at 25 degrees C but not at 15 degrees C. Hematocrit and [hemoglobin] rose significantly during graded hypoxia at 25 degrees C but did not change at 15 degrees C. Toads exposed to 10% O2 (the value that elicits behavioral hypothermia) showed a significant respiratory alkalosis at 25 degrees C but not at 15 degrees C. Likewise, hypoxia caused a significant drop in SaO2 and PO2 at 25 degrees C. Cooling to 15 degrees C during hypoxia caused a significant rise in SaO2 but no change in PaO2. In conclusion, behavioral hypothermia is a beneficial response to hypoxia in Bufo marinus.

Thermal preferences of resistant and susceptible strains ofBiomphalaria glabrata(Gastropoda) exposed toschistosoma mansoni(Trematoda)

Parasitology ◽  
1991 ◽  
Vol 103 (3) ◽  
pp. 357-362 ◽  
Author(s):  
H. Lefcort ◽  
C. J. Bayne
Keyword(s):  
Schistosoma Mansoni ◽  
Resistant Strain ◽  
Thermal Gradient ◽  
Biomphalaria Glabrata ◽  
Defense System ◽  
Significant Drop ◽  
Preferred Temperature ◽  
Post Exposure ◽  
The Mean ◽  
Thermal Preferences

The thermal preferences of two strains of the snailBiomphalaria glabrata, one resistant to, and one susceptible to, the parasiteSchistosoma mansoniwere determined in an aquatic thermal gradient. Snails were tested without exposure to the parasite, and 2 h and 5 weeks after exposure to trematode miracidia. The mean temperature selected by susceptible strain snails 2 h post-exposure tended to be lower than that of unexposed controls, although this was not statistically significant. In this strain, at 5 weeks post-exposure, the preferred temperature dropped by 1.9±0.5°C. The resistant strain displayed a significant drop of 1.8±0.6°C 2 h post-exposure. These results are consistent with the hypothesis that a drop in mean temperatures selected by snails is due to altered levels of endogenous cytokines such as IL-1 or TNF in association with parasite activation of the snail internal defense system.

scholarly journals Low‐Level Tragus Stimulation Modulates Atrial Alternans and Fibrillation Burden in Patients With Paroxysmal Atrial Fibrillation

2021 ◽  
Author(s):  
Kanchan Kulkarni ◽  
Jagmeet P. Singh ◽  
Kimberly A. Parks ◽  
Demosthenes G. Katritsis ◽  
Stavros Stavrakis ◽  
...  
Keyword(s):  
Atrial Fibrillation ◽  
Significant Rise ◽  
P Wave ◽  
Significant Drop ◽  
Electrical Nerve Stimulation ◽  
Low Level ◽  
Potential Marker ◽  
Control Stimulation ◽  
Active Patients

Background Low‐level tragus stimulation (LLTS) has been shown to significantly reduce atrial fibrillation (AF) burden in patients with paroxysmal AF. P‐wave alternans (PWA) is believed to be generated by the same substrate responsible for AF. Hence, PWA may serve as a marker in guiding LLTS therapy. We investigated the utility of PWA in guiding LLTS therapy in patients with AF. Methods and Results Twenty‐eight patients with AF were randomized to either active LLTS or sham (earlobe stimulation). LLTS was delivered through a transcutaneous electrical nerve stimulation device (pulse width 200 μs, frequency 20 Hz, amplitude 10–50 mA), for 1 hour daily over a 6‐month period. AF burden over 2‐week periods was assessed by noninvasive continuous ECG monitoring at baseline, 3 months, and 6 months. A 5‐minute control ECG for PWA analysis was recorded during all 3 follow‐up visits. Following the control ECG, an additional 5‐minute ECG was recorded during active LLTS in all patients. At baseline, acute LLTS led to a significant rise in PWA burden. However, active patients receiving chronic LLTS demonstrated a significant reduction in both PWA and AF burden after 6 months ( P <0.05). Active patients who demonstrated an increase in PWA burden with acute LLTS showed a significant drop in AF burden after 6 months of chronic LLTS. Conclusions Chronic, intermittent LLTS resulted in lower PWA and AF burden than did sham control stimulation. Our results support the use of PWA as a potential marker for guiding LLTS treatment of paroxysmal AF.

Balancing hypoxia and hypothermia in cold-submerged frogs.

1997 ◽  
Vol 200 (6) ◽  
pp. 1031-1038 ◽  
Author(s):  
G J Tattersall ◽  
R G Boutilier
Keyword(s):  
Thermal Gradient ◽  
Rana Temporaria ◽  
Metabolic Effects ◽  
Experimental Chamber ◽  
Hypoxic Stress ◽  
Profound Hypothermia ◽  
Preferred Temperature ◽  
Chemical Conditions ◽  
Acute Changes ◽  
Ice Water

Many animals respond to hypoxic stress by selecting cooler environments, the so-called 'behavioural hypothermia' response. Amphibians overwintering in ice-covered ponds and lakes offer an ecologically relevant test of this response since they must choose between the confounding metabolic effects of profound hypothermia or hypoxia; thermal and chemical conditions can vary from 0 degrees C and normoxic at the ice-water interface to 4 degrees C and markedly hypoxic at depths of 2-4 m. To mimic such environmental conditions, we constructed an experimental chamber that enabled continuous electronic surveillance of an animal's movement along a thermal gradient. When Rana temporaria pre-acclimated to 3.5 degrees C were placed in a normoxic thermal gradient ranging from 0.8 to 8 degrees C, they invariably favoured the warmer end of the chamber. Upon exposure to hypoxia, however, their preferred temperature shifted from a median of 6.8 degrees C (P02 = 158 mmHg; 1 mmHg = 0.133 kPa) to 1.9 degrees C (P02 = 25 mmHg). Metabolic rate measurements from animals exposed simultaneously to acute changes in water temperature and PO2 suggest that movement to colder conditions in hypoxia effects the greatest metabolic savings and prolongs the onset of a plasma lactacidosis.

Ventilatory response to transient hyperoxia in head injury hyperventilation

1980 ◽  
Vol 49 (1) ◽  
pp. 52-58 ◽  
Author(s):  
A. G. Leitch ◽  
J. E. McLennan ◽  
S. Balkenhol ◽  
R. L. McLaurin ◽  
R. G. Loudon
Keyword(s):  
Head Injury ◽  
Ventilatory Response ◽  
Minute Ventilation ◽  
Respiratory Control ◽  
Normal Subjects ◽  
Respiratory Alkalosis ◽  
Cerebral Injury ◽  
Peripheral Chemoreceptor ◽  
Male Patients ◽  
Almost All

We have measured breath-by-breath instantaneous minute ventilation (VIinst) before, during, and after the administration of 10 breaths of 100% oxygen to seven male patients with head injury hyperventilation. The patients were hypoxemic (PaO2 61.2 ± 6.3) and hypocapnic (PaCO2 26.6 ± 5.9) with a respiratory alkalosis (pH 7.53 ± 0.06) while breathing air. Following the oxygen VIinst fell on the average by 40 ± 12.7% from 16.06 ± 3.75 1.min-1 to a minimum of 9.73 ± 3.20 1.min-1 at 20.4 ± 2.9 s after the first breath of oxygen. In the majority of our hyperventilating patients, almost all of the resting hyperventilation could be abolished transiently by 100% oxygen. This fall in ventilation represents the peripheral chemoreceptor contribution to resting ventilation and is increased in the head injury patients in comparison with normal subjects breathing air or hypoxic gas mixtures, altitude-acclimatized subjects and patients who are hypoxic because of chronic bronchitis or interstitial lung disease. We suggest that the increased reflex hypoxic drive to ventilation found in our patients is secondary to their cerebral injury, resulting in a reduction of descending cortical inhibitory influences on the medullary respiratory control centers.

Interactions between cellular respiration and thermoregulation in the paramecium

1994 ◽  
Vol 267 (1) ◽  
pp. R349-R352 ◽  
Author(s):  
G. M. Malvin ◽  
P. Havlen ◽  
C. Baldwin
Keyword(s):  
Oxidative Phosphorylation ◽  
Thermal Gradient ◽  
Oxygen Supply ◽  
Cellular Respiration ◽  
Maximal Response ◽  
Adaptation To Hypoxia ◽  
Cellular Mechanisms ◽  
Beneficial Response ◽  
Lower Temperature ◽  
Maximal Reduction

An important adaptation to hypoxia is a regulated reduction in body temperature because it lowers metabolic rate when oxygen supply is limited. Although this beneficial response occurs in organisms ranging from protozoans to mammals, little is known of the cellular mechanisms responsible for the hypoxia-induced reduction in temperature. Using the unicellular protozoan, Paramecium caudatum, we showed that inhibition of oxidative phosphorylation with sodium azide (NaN3) under normoxic conditions mimics the thermoregulatory effects of hypoxia, causing this species to select a lower temperature in a thermal gradient (P < 0.0001). Under control conditions, selected temperature (Tsel) was 28.3 +/- 0.3 degrees C. NaN3 concentrations of 0.1 mM and above significantly reduced Tsel (P < 0.0001). Ten millimolar NaN3 produced the maximal reduction in Tsel, 11.4 degrees C, and the dose that produced 50% of the maximal response was 0.7 mM. The reduction in temperature was beneficial because both O2 consumption and survival were significantly less affected by NaN3 at lower temperatures. These results suggest that O2 does not directly affect thermoregulation in the paramecium. Rather, the hypoxia-induced reduction in Tsel results from inhibition of oxidative phosphorylation.

Ventilatory effects of acetazolamide in cats during hypoxemia

1992 ◽  
Vol 72 (5) ◽  
pp. 1717-1723 ◽  
Author(s):  
L. J. Teppema ◽  
F. Rochette ◽  
M. Demedts
Keyword(s):  
Steady State ◽  
Ventilatory Response ◽  
Significant Rise ◽  
Hypoxic Ventilatory Response ◽  
Peripheral Chemoreceptor ◽  
Peripheral Chemoreceptors ◽  
Relative Contribution ◽  
Ventilatory Effects ◽  
Arterial Po2 ◽  
Mean Alveolar Pco2

In normoxemic cats, acetazolamide (ACTZ) has been shown to cause a large rise in ventilation (VE) but a decrease in peripheral chemoreceptor activity. The relative contribution of the peripheral chemoreceptors to ventilation is higher during hypoxemia than during normoxemia. Therefore, what are the effects of ACTZ during steady-state hypoxemia? The aims of this study in anesthetized cats were 1) to study the effect of ACTZ (50 mg/kg iv) on mean hypoxemic [arterial PO2 (PaO2) approximately 6 kPa] ventilation and 2) to study the effect of ACTZ on the isocapnic hypoxic ventilatory response. In the first study, in six cats with an inspiratory CO2 fraction of 0, ACTZ led to an insignificant rise in mean VE of 119 ml.min-1.kg-1 after 1 h. In five other cats maintained at an inspiratory CO2 fraction of 0.015, ACTZ resulted in a significantly larger response in VE (268 and 373 ml.min-1.kg-1 after 1 and 2 h, respectively). In the second study, before infusion in five cats, an isocapnic fall in mean PaO2 from 13 to 4.7 kPa led to a significant rise in mean VE of 385 ml.min-1.kg-1; 1 h later, the response (at the same mean alveolar PCO2) was reduced to an insignificant rise of 38 ml.min-1.kg-1. Before infusion four other cats showed a significant rise in mean VE of 390 ml.min-1.kg-1 when mean PaO2 was lowered isocapnically from 12.4 to 6.8 kPa; 2 h after infusion, an isocapnic fall in mean PaO2 from 13.9 to 7.2 kPa led to an insignificant rise of 112 ml.min-1.kg-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Temperature regulation in mice during withdrawal from ethanol dependence

1994 ◽  
Vol 267 (4) ◽  
pp. R929-R934 ◽  
Author(s):  
L. I. Crawshaw ◽  
C. S. O'Connor ◽  
J. C. Crabbe ◽  
D. L. Hayteas
Keyword(s):  
Temperature Regulation ◽  
Thermal Gradient ◽  
Ethanol Vapor ◽  
Analysis Of Covariance ◽  
Control Group ◽  
Preferred Temperature ◽  
Ethanol Dependence ◽  
Hypermetabolic State ◽  
The Difference ◽  
Increased Activity

Temperature regulation during withdrawal from ethanol dependence was studied in mice. Dependence was induced utilizing ethanol vapor inhalation combined with injections of pyrazole, an alcohol dehydrogenase inhibitor. One control group received vehicle (0.9% NaCl); another received pyrazole (68.1 mg/kg) in vehicle. During withdrawal, mice were placed in a thermal gradient, with core temperature (Tc) and preferred temperature (Tpref) continuously recorded for 26 h. During the period of maximal withdrawal severity (4-10 h after removal from ethanol vapor), the withdrawal group was more active than controls. Withdrawal group Tc [36.4 +/- 0.1 (SE) degrees C] was similar to that of NaCl (36.2 +/- 0.1 degrees C) and pyrazole (36.3 +/- 0.2 degrees C) controls. Withdrawal group Tpref (30.5 +/- 0.5 degrees C) was significantly lower than either NaCl (33.5 +/- 0.3 degrees C) or pyrazole (32.9 +/- 0.5 degrees C) controls. Analysis of covariance with activity as covariate indicated that the difference between Tc and Tpref was greater for the withdrawal group and was due to more than increased activity. Mice withdrawing at constant temperature (29.5 degrees C) did not show Tc different from that of controls. These results support the conclusion that regulated body temperature is not altered during withdrawal. We propose that the lower Tpref of withdrawing mice represents a means of dissipating excess heat that is partly generated by the hypermetabolic state accompanying withdrawal from ethanol dependence.

Distributions of diploid and pentaploid brine shrimp Artemia parthenogenetica in an illuminated thermal gradient

1991 ◽  
Vol 69 (9) ◽  
pp. 2461-2465 ◽  
Author(s):  
Hugh Lefcort ◽  
Lei Zhang ◽  
Charles E. King
Keyword(s):  
Behavioral Response ◽  
Thermal Gradient ◽  
Brine Shrimp ◽  
Horizontal Gradients ◽  
Light Gradient ◽  
Artemia Parthenogenetica ◽  
Light Intensities

We explored the behavioral response to horizontal gradients of light and heat of sympatric diploid and pentaploid Artemia parthenogenetica. When exposed to a uniformly illuminated thermal gradient, pentaploids had a mean distribution that was oriented toward temperatures 2.9 °C higher than that of diploid animals. In a light gradient, diploids were distributed at higher light intensities than pentaploids. When the distributions in an evenly illuminated thermal gradient were compared with those occurring when thermal and light gradients ran in opposite directions, it was found that diploids tended to occur at lower temperatures, whereas pentaploid distributions were not significantly different for the two conditions. Our findings suggest that pentaploids are not as strongly attracted to light as diploids, in either the presence or the absence of a thermal gradient. We predict that in the field, warmer areas of a pond may be exploited by pentaploids during the day and by diploids during the night.

Metabolic rate, respiratory exchange ratio, and apneas during meditation

1989 ◽  
Vol 256 (3) ◽  
pp. R632-R638 ◽  
Author(s):  
J. Kesterson ◽  
N. F. Clinch
Keyword(s):  
Metabolic Rate ◽  
Respiratory Exchange Ratio ◽  
Transcendental Meditation ◽  
Interaction Effects ◽  
Co2 Production ◽  
O2 Consumption ◽  
Significant Trial ◽  
Significant Drop ◽  
Eyes Closed ◽  
Marked Decline

We tested the hypothesis that a drop in metabolic rate (MR) causes the apneas observed in some subjects during transcendental meditation (TM). We measured O2 consumption (VO2) and CO2 production (VCO2) in three groups of experienced meditators and one group of nonmeditating controls. Measurements were made before, during, and after TM for the meditators and before, during, and after eyes-closed relaxation for the nonmeditating controls. The three groups of meditators consisted of 1) those showing little change in the frequency of ventilation (f) with meditation, 2) those showing a marked decline in f, and 3) those showing numerous apneas and a marked fall in f. There were significant trial effects but no group or interaction effects for the decline in VO2. Thus we concluded that a drop in MR is not the cause of the apneas. However, there were significant trial and interaction effects for the changes in VCO2 and the respiratory exchange ratio (R), with a significant drop in R for the meditators but not for the controls. We report additional evidence and speculate that the drop in R is a consequence of mild hypoventilation.

PLASMA ANDROGENS IN WOMEN

1964 ◽  
Vol 45 (2) ◽  
pp. 254-271 ◽  
Author(s):  
W. J. Dignam ◽  
R. J. Pion ◽  
E. J. Lamb ◽  
H. H. Simmer
Keyword(s):  
Clinical Manifestations ◽  
Unknown Origin ◽  
Mean Value ◽  
Significant Rise ◽  
Plasma Testosterone ◽  
List Type ◽  
Polycystic Ovaries ◽  
Significant Drop ◽  
Mean Values ◽  
Normal Women

ABSTRACT Plasma levels of conjugated DHEA, conjugated androsterone (modified method of Migeon & Plager) and testosterone (method of Finkelstein et al.) were determined in a group of 20 patients with polycystic ovaries and hirsutism or virilism, before and after intravenous HCG stimulation and ACTH-suppression with dexamethasone. Mean values for testosterone, conjugated DHEA and androsterone were.34 ±.24 μg/100 ml, 50.9 ± 28.3 μg/100 ml and 31.4 ± 19.4 μg/100 ml respectively, all significantly higher than levels found in normal women. In all, but 3 cases, testosterone values were above the 2-sigma range of normal women in contrast to the frequent overlapping observed for conjugated DHEA and androsterone. HCG stimulation led to a significant rise in the mean value of testosterone (.61 ±.22 μg/100 ml) but little change was seen in those of the conjugates. While dexamethasone caused a marked decrease of testosterone in only 2 patients, it led to a pronounced fall in DHEA values and a lesser but significant drop in androsterone concentrations in most patients. In patients with a unilateral polycystic or with bilateral polycystic ovaries but without hirsutism or virilism similar values were noted. Two patients with arrhenoblastomas, 4 patients with adrenal disorders and 13 patients with hirsutism of unknown origin were studied and their findings presented. All patients with hirsutism or virilism had a higher mean value of testosterone than did normal women. The testosterone levels did not parallel the severity, although a correlation did seem to exist in the mildly and moderately hirsute patients. Plasma androgen determinations in general and plasma testosterone studies, in particular, while helpful in elucidating the clinical manifestations of masculinization do not allow the investigator to differentiate an adrenal from an ovarian source. Adjunctive studies, utilizing HCG and dexamethasone, are helpful, but not conclusive.

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