Role In Thermoregulation Research Articles

Behavioral thermoregulation inpalmipenna aeoleoptera (neuroptera): Do the hypertrophied hindwings play a role?

The hypertrophied hindwings of Palmipenna aeoleoptera (Neuroptera) were examined for a possible thermoregulatory role. These wings arise from basal stalks which expand into large, flattened, darkly pigmented, and vascularized dilations. During the cooler times of the day the insects basked by crouching with the body and hindwings held horizontally in contact with rocks. As air temperatures increased, insects stilted with the hindwings held at 90° to the horizontal. Thoracic temperatures of these ectotherms correlated with air temperatures (Tthorax = 1.55Tair −10.99), with maximum recorded thoracic temperatures of 47°C. No differences were found between thoracic temperatures of males and those of females, although males had far larger hindwings. Live insects caught on rocks were consistently cooler than dead insects (operational temperature thermometers) on rocks. This may be attributed to convective cooling in flight just prior to capture, and stilting, behavior patterns that were frequent during the hottest times of the day. Thoracic temperatures of insects resting on rocks were frequently higher than operational temperature thermometers in air, suggesting that warming resulted from basking on rocks. The minimum body temperature for flight was 27°C. In the laboratory, hindwing ablation altered neither the rate (using time constants) of heating or cooling nor the equilibrium temperature of the body, showing that the hindwings play no direct role in heat uptake or loss.

Phenotypic Adaptation and Natural Selection in the Wild Rabbit, Oryctolagus cuniculus, in Australia

(3) Genetic differences among regional populations were detected from the persistence of traits through two generations of rearing under standardized conditions. Differences in the shape of the body core were consistent with prior genetic adaptation to regional ambient temperature. Other genetic adaptations or founder effects caused divergence in size of the ears and pes. (4) The size of the ears differed adaptively among regional field populations, being longer in warmer climates, apparently because genetic differences interacted with phenotypic responses to heat. (5) The pinnae have thermoregulatory functions and responded phenotypically to ambient temperature during growth in two generations. In contrast, the pes lack a thermoregulatory role and grew independently of ambient temperature, but responded to other environmental factors.

Differential Effects of Antihypertensive Drugs on Nutritive and Nonnutritive Blood Flow in Anaesthetized Rabbits

Arteriovenous (AV) shunt vessels connect arterioles directly to the venous side. These vessels play a role in thermoregulation and in the pathophysiology of migraine. Tracer microspheres are excellent tools to study drug effects on AV anastomoses. Microspheres with a diameter of 15 microns are unable to pass through capillary vessels, but they readily cross AV shunt vessels and are transported to the lungs and trapped there. We investigated the effects of antihypertensive agents on AV shunt flow in anaesthetized rabbits and we also measured nutritional blood flow in the ear, an organ known to have both nutritional and AV shunt vessels. Nitroprusside sodium tended to increase and prazosin strongly increased AV shunt flow. The calcium antagonist isradipine, by contrast, decreased AV shunt flow even though it is also a vasodilator. Spirapril, an angiotensin-converting enzyme inhibitor, elicited similar effects. The centrally acting antihypertensive agent guanfacine strongly decreased AV shunt flow. These effects did not correlate with the drug effects on nutritional blood flow, which were, however, so variable that none of them reached statistical significance. The following trends were seen: nitroprusside sodium, isradipine, and guanfacine increased nutritional blood flow, but prazosin, a dilator of AV shunts, did not. The amount of blood crossing through AV shunts from the arterial to the venous side is considerable (up to 15% of cardiac output before drugs). A drug-induced increase is not associated with an apparent benefit but causes a hyperdynamic circulation that might contribute to the hemodynamic load of the heart.

Differential Effects of Antihypertensive Drugs on Nutritive and Nonnutritive Blood Flow in Anaesthetized Rabbits

Arteriovenous (AV) shunt vessels connect arterioles directly to the venous side. These vessels play a role in thermoregulation and in the pathophysiology of migraine. Tracer microspheres are excellent tools to study drug effects on AV anastomoses. Microspheres with a diameter of 15 microns are unable to pass through capillary vessels, but they readily cross AV shunt vessels and are transported to the lungs and trapped there. We investigated the effects of antihypertensive agents on AV shunt flow in anaesthetized rabbits and we also measured nutritional blood flow in the ear, an organ known to have both nutritional and AV shunt vessels. Nitroprusside sodium tended to increase and prazosin strongly increased AV shunt flow. The calcium antagonist isradipine, by contrast, decreased AV shunt flow even though it is also a vasodilator. Spirapril, an angiotensin-converting enzyme inhibitor, elicited similar effects. The centrally acting antihypertensive agent guanfacine strongly decreased AV shunt flow. These effects did not correlate with the drug effects on nutritional blood flow, which were, however, so variable that none of them reached statistical significance. The following trends were seen: nitroprusside sodium, isradipine, and guanfacine increased nutritional blood flow, but prazosin, a dilator of AV shunts, did not. The amount of blood crossing through AV shunts from the arterial to the venous side is considerable (up to 15% of cardiac output before drugs). A drug-induced increase is not associated with an apparent benefit but causes a hyperdynamic circulation that might contribute to the hemodynamic load of the heart.

SLEEPING POSITION AND INFANT BEDDING MAY PREDISPOSE TO HYPERTHERMIA AND THE SUDDEN INFANT DEATH SYNDROME

Southern New Zealand has one of the highest postneonatal mortality rates in the developed world (8·1/1000 livebirths) and 77% of these deaths are attributed to the sudden infant death syndrome (SIDS). Both hyperthermia and sleeping position have previously been implicated in SIDS. A theoretical model to estimate the thermal balance of infants used here shows that the head, and particularly the face, becomes the main route for heat loss when thick clothing and bedding are used. This thermoregulatory role could be compromised by the prone sleeping position. It is postulated that particular cultural combinations of infant care practices (sleeping position, clothing, bedding, and room heating) may facilitate hyperthermia and explain widely disparate rates of SIDS in different countries and ethnic groups.

Receptor binding sites for atrial natriuretic factor are expressed by brown adipose tissue.

To explore the possibility that atrial natriuretic factor (ANF) is involved in thermoregulation we used quantitative receptor autoradiography and homogenate receptor binding assays to identify ANF bindings sites in neonatal rat and sheep brown adipose tissue, respectively. Using quantitative receptor autoradiography were were able to localize high levels of specific binding sites for 125I-rat ANF in neonatal rat brown adipose tissue. Homogenate binding assays on sheep brown fat demonstrated that the radioligand was binding to the membrane fraction and that the specific binding was not due to a lipophilic interaction between 125I-rat ANF and brown fat. Specific binding of 125I-rat ANF to the membranes of brown fat cells was inhibited by unlabeled rat ANF with a Ki of 8.0 x 10(-9) M, but not by unrelated peptides. These studies demonstrate that brown fat cells express high levels of ANF receptor binding sites in neonatal rat and sheep and suggest that ANF may play a role in thermoregulation.

Oscillating heat flow from rabbit's pinna.

Thermal characteristics of the pinnae of the ears of New Zealand White rabbits (Oryctolagus cuniculus) were measured with an infrared imaging system, and vasomotor oscillations were observed to occur spontaneously in the pinnae of all rabbits at an ambient temperature of 20 degrees C. Measured fluctuations in surface temperature were used to characterize the observed vasomotor oscillations, whereas heat loss from the pinnae was calculated using the mean pinna temperatures. The pulsing related to thermoregulation had a mean frequency of approximately 0.025 Hz with a mean amplitude of approximately 0.35 degrees C. When surface temperature was measured simultaneously from both pinnae of individual rabbits, the thermal pulsing was synchronous in the two pinnae. Many of the characteristics of the vasomotor rhythm measured in the pinnae of rabbits were consistent with an active and controlled oscillation, and a possible thermoregulatory role for a controlled vasomotor oscillation is discussed.

The opioid system and temperature regulation.

Opioid drugs and endogenous opioid peptides exert profound effects on body temperature. The particular effect seen is dependent on species, ambient temperature, degree of restraint imposed on the subject, route of drug administration, and a number of other factors. A major determinant is the opioid receptor type with which the agonist forms a complex. Evidence is accumulating that opioid ligands and opioid receptors play a functional role in thermoregulation, even though the opioid system may not be tonically active. Although further studies are needed to fully define the role and the mechanisms involved, as well as the generality of the role in a variety of species, a reasonable working hypothesis is that mu receptors in the rat and the mouse are involved in responses that result in heat gain, while K receptor activation results in opposite responses. To a large extent, the mu receptors in the rat appear to be located primarily in the brain, while the K receptors are outside the brain and perhaps even outside of the central nervous system. At present there is no evidence of involvement of delta receptors in thermoregulation. A fuller understanding of the opioid system and its role in thermoregulation will have broad clinical implications, as well as provide insights into interactions among the several neurotransmitter systems involved in thermoregulatory control of body temperature.

Effect of prolactin inhibition on thermophysiological parameters, water and feed intake of sun-exposed male Creole goats ( Capra hircus) in Guadeloupe (French West Indies)

1. 1.|Thermoregulatory ability of sun-exposed Creole bucks (a tropical dwarf breed), measured by respiratory rate (RR), rectal temperature (RT), water and feed intake, was tested in animals with prolactin (PRL) secretion suppressed by 2 bromo-α-ergocryptine and compared to animals with intact PRL secretion. 2. 2.|Bucks with suppressed PRL secretion exhibited a significant rise of RT although their RR increased more than in untreated bucks. This thermoregulation failure occurred only at the hottest hours of the day (12.00) when the radiant heat load was the highest as indicated by “black-globe temperature” ( T g). 3. 3.|Dry matter and water consumption were not affected by the treatment. 4. 4.|In our opinion, PRL plays a role in thermoregulation of the goat under hot climates.

Effects of physiological manipulations on locus coeruleus neuronal activity in freely moving cats. I. Thermoregulatory challenge

This and the following two papers examine the activity of locus coeruleus noradrenergic (LC-NE) neurons in response to a variety of physiological manipulations in unanesthetized, unrestrained cats. Unit responses were studied during a constant behavioral state in order to avoid the potentially confounding effects of state changes upon LC-NE unit discharge. In the present study, LC-NE unit activity was recorded during two thermoregulatory challenges: ambient heating and pyrogen-induced fever. These two conditions are particularly interesting since the direction of body temperature change that they produce is the same, but the thermoregulatory responses elicited are opposite, i.e. heat loss and heat gain. LC-NE neurons were activated by both manipulations. In response to ambient heating, neuronal activity increased only with the occurrence of panting, and not during earlier portions of the heating session. Following pyrogen administration, LC-NE neurons responded only during the peak increase in body temperature. Both of these effects on unit activity occurred independent of changes in behavioral state. Since both manipulations similarly increased LC-NE unit activity, despite eliciting opposite thermoregulatory responses, it appears that these neurons do not play a specific role in thermoregulation, but may participate in the response to physiological challenges in general.

A sternal gland in the Siamang Gibbon(Hylobates syndactylus)

The present report gives the first description of a sternal gland in the siamang gibbon, Hylobates syndactylus,and the first histological examination of a sternal gland in a hominoid primate other than the orang-utan. The gland does not seem to be used for any kind of marking behavior, in contrast to the sternal glands in many other primates and some other mammals. The sternal gland of the siamang may be derived from a marking gland which specialized secondarily to serve parallel functions like those served by the axillary organs of humans and the African apes. A role of the gland in olfactory communication and a possible minor role in thermoregulation are discussed.

Alterations in α-Adrenergic and Muscarinic Cholinergic Receptor Binding in Rat Brain Following Nonionizing Radiation

Microwave radiation produces hyperthermia. The mammalian thermoregulatory system defends against changes in temperature by mobilizing diverse control mechanisms. Neurotransmitters play a major role in eliciting thermoregulatory responses. The involvement of adrenergic and muscarinic cholinergic receptors was investigated in radiation-induced hyperthermia. Rats were subjected to radiation at 700 MHz frequency and 15 mW/cm2 power density and the body temperature was raised by 2.5 degrees C. Of six brain regions investigated only the hypothalamus showed significant changes in receptor states, confirming its pivotal role in thermoregulation. Adrenergic receptors, studied by [3H]clonidine binding, showed a 36% decrease in binding following radiation after a 2.5 degrees C increase in body temperature, suggesting a mechanism to facilitate norepinephrine release. Norepinephrine may be speculated to maintain thermal homeostasis by activating heat dissipation. Muscarinic cholinergic receptors, studied by [3H]quinuclidinyl benzilate binding, showed a 65% increase in binding at the onset of radiation. This may be attributed to the release of acetylcholine in the hypothalamus in response to heat cumulation. The continued elevated binding during the period of cooling after radiation was shut off may suggest the existence of an extra-hypothalamic heat-loss pathway.

Opiate receptor mediated hyperthermic responses in rat following Ca++ channel antagonists

The effects of morphine sulfate on rectal temperature and on Ca++-stimulated Mg++ATPase activity in crude synaptosomal fraction (P2) of cortex, hypothalamus and cerebellum were investigated in rat. Morphine (3-15 mg/kg, SC) produced hyperthermia at 30-120 min after the drug administration. The Ca++/Mg++ ATPase activity in hypothalamus and cortex was decreased while there was no change in Mg++ ATPase activity. The enzyme activity in cerebellum was not affected. The opiate antagonist naloxone hydrochloride (5 mg/kg, SC) antagonized the effect of morphine on rectal temperature and Ca++/Mg++ ATPase activity. The effects of different calcium channel antagonists (nimodipine 1 mg/kg, verapamil 2.5 mg/kg and diltiazem 10 mg/kg, SC) on the changes induced by morphine were also investigated. These antagonists not only antagonized morphine hyperthermia, but also the inhibitory effect of morphine on Ca++/Mg++ ATPase activity in hypothalamus. The calcium channel agonist BAY K8644 (3 mg/kg, SC) produced hypothermia and also stimulation of Ca++/Mg++ ATPase activity in hypothalamus. Naloxone failed to alter these effects of BAY K8644. These studies demonstrate that Ca++ transport in hypothalamus, as indicated by Ca++/Mg++ ATPase activity, plays an important role in thermoregulation and thermoregulatory changes induced by opiates.

Metabolic and morphologic changes in brown adipose tissue from non‐growing mice with an isogeneic sarcoma. Evaluation with respect to development of cachexia

Brown adipose tissue plays a thermoregulatory role influencing energy balance in experimental animals and possibly also in humans. In the present study we have reevaluated whether brown adipose tissue may contribute to the development of cancer cachexia in non-growing mice bearing an isogeneic tumor. Interscapular brown adipose tissue mass decreased by 20% in freely-fed sarcoma-bearing mice housed at room temperature. Increased mitochondrial density and increased oxidation rate of acetate at low acetate concentrations were found in brown fat from sarcoma-bearing mice, while the oxidation capacity was unchanged compared with that of freely-fed controls. Metabolic and morphologic changes in brown fat from sarcoma-bearing mice were similar to those found in weight-paired controls, which had experienced the same loss of body weight as the tumor-bearing mice. Selective and non-selective B-receptor blockade and surgical removal of interscapular brown fat before tumor implantation did not influence the nutritional state of freely-fed tumor-bearing mice. Injections of noradrenaline caused a proportionately lower increase in oxygen uptake in tumor-bearing animals than in freely-fed controls. Exposure to cold (+5 degrees C) doubled food intake and led to hypertrophy of brown fat in both sarcoma-bearing mice and control animals. Tumor growth was lower although not statistically different in animals housed at +5 degrees C compared with animals housed at +25 degrees C. It is concluded that brown adipose tissue from sarcoma-bearing mice could not account quantitatively for the host wasting in tumor-bearing mice housed at room temperature.

Comparison of influences of stimulation of the Ammon's horn and subiculum to thermosensitive preoptic and septal neurons.

Thermosensitive preoptic and septal (PO/SP) neurons were studied for their responsiveness to electrical stimulation of the dorsal Ammon's horn (DAH) and the ventral subiculum (VSB) of the hippocampal formation in the rat. DAH stimulation affected only 14 (16%) of 90 PO/SP thermosensitive neurons whereas VSB stimulation affected 77 (86%) units. The results suggests that the DAH has no major role in thermoregulation in the rat.

Activity patterns of terrestrial gamebirds in the Willem Pretorius Game reserve, Orange Free State

Activity patterns of the Natal francolin (Francolinus natalensis), Swaison’s francolin (F. swaisoni) and the crowned guinea-fowl (Numida meleagris) appear to be influenced mainly by climatic conditions, either directly or indirectly. Diurnal activities are characterised by early-morning and late-afternoon peaks and long periods of rest during the middle of the day. Feeding is the most important activity of the birds, followed by maintenance and strenuous activities. Seasonal and species-specific preferences in the use of shade apparently play an important thermoregulatory role. In comparison to behaviour patterns carried out in direct sunlight, shade-associated behaviour tends to a greater extent to be dominated by maintenance activities, especially during the wet season.

Thermal responses to central angiotensin II, SQ 20881, and dopamine infusions in sheep

The thermoregulatory role of brain angiotensin II (ANG II) was tested by intracerebroventricular (IVT) infusion of ANG II or the converting enzyme inhibitor SQ 20881 (SQ) in 15 conscious sheep. Deep body temperature decreased 0.30 +/- 0.07 degree C (SE) during the 3-h period of IVT ANG II (25 ng/min) infusion (P less than 0.05) and increased 0.50 +/- 0.13 degree C during IVT SQ (1 microgram/min) infusion (P less than 0.01). To determine whether the rise in body temperature after IVT SQ infusion might be the result of a central renin-angiotensin system (RAS), SQ was infused IVT in five conscious sheep 20 h after bilateral nephrectomy. This resulted in a significant rise in body temperature of 0.28 +/- 0.05 degree C (P less than 0.05). When vasopressin antidiuretic hormone (ADH) was infused intravenously at the same time of IVT SQ infusion, the rise in temperature was depressed, but ADH did not lower the temperature below basal. IVT dopamine (20 micrograms/min) increased body temperature by 0.40 +/- 0.04 degree C (P less than 0.01), which was qualitatively similar to the result with IVT SQ. These data support the hypothesis that endogenous brain ANG II may play a role in thermoregulation. Furthermore, plasma ADH level, regulated in part by brain ANG II, is probably not the mediator of that thermoregulation. The similar effects of IVT dopamine and SQ on body temperature strengthen the hypothesis that dopamine may be involved in the central action of brain ANG II.

Changes in plasma cortisol during acute cold exposure in euthermic European hedgehogs: thermoregulatory role of the hypothalamo-pituitary-adrenal axis

During acute cold exposure regulatory heat production of European hedgehogs was significantly increased with a simultaneous rise in the plasma cortisol level. Soon after cold exposure, at the time when standard metabolic rate was measured, the plasma cortisol level was reduced again. This finding indicates a highly reactive hypothalamo-pituitary-adrenal axis in euthermic hedgehogs exposed to a cold environment. Two effects of the adrenocorticostatic agent metopirone ditartrate were observed: (1) A metopirone-induced increase in nonshivering thermogenesis (NST) starting 18 min after application, reaching a maximum after 43 min and disappearing after 90 min (Fig. 1, Table 1). Simultaneously a profound long lasting hyperglycemia was observed (Fig. 2). (2) In contrast to untreated hedgehogs, animals which were given metopirone did not show an increase in the plasma cortisol level, when exposed to cold within 2 to 3 h (Fig. 6). When animals were pretreated with dexamethasone the metopirone-induced NST was suppressed, indicating that the effect of metopirone is mediated by the hypothalamo-pituitary-adrenal system (Fig. 4). The effect of metopirone at doses used in this study was reversible. It is suggested that a combined action of corticosteroids and catecholamines is involved in the control of regulatory heat production.

Increased contribution of brown adipose tissue to nonshivering thermogenesis in the Djungarian hamster during cold-adaptation.

The effect of cold-adaptation was investigated on the brown adipose tissue of Djungarian hamsters. Animals maintained at 23 degrees C and 16 hours light per day (controls) were exposed to 5 degrees C. The wet weight of the total brown fat is reduced by some 40% within 4 days of cold-exposure, as a result of extensive triacylglycerol depletion of the tissue with no reduction in DNA; the tissue mass remains constant under persistent cold influence. The total amount of tissue mitochondria is doubled by 24 h and increases by a factor of 3 under persistent cold-stimulus, the specific respiratory capacity of the organelles remaining unchanged. The amount of 32 kDa regulatory protein per mg mitochondrial protein quantified from high-affinity GDP-binding, is increased by a factor of 2.7 after 21 days of cold-adaptation; a 9-fold increment is found of the total mitochondrial GDB-binding capacity. Comparison of nonshivering thermogenesis and the maximal thermogenic capacity of brown fat, estimated from the maximal respiration of the isolated mitochondria and the total amount of mitochondria in the tissue, suggests that brown fat may contribute about 20% to the whole-body nonshivering thermogenesis in warm-adapted controls and 45% in cold-adapted hamsters. The estimated increase in thermogenic capacity of the tissue in response to 21 days of cold-adaptation corresponds to the increase in nonshivering thermogenesis, suggesting a central thermoregulatory role of brown fat during cold-adaptation.

Biochemical aspects of the thermoregulatory role of brown adipose tissue

1.1. Specific GDP-binding in brown adipose tissue (BAT) mitochondria is increased by 50% in Djungarian hamsters after 70 days of exposure to a short photoperiod at 23°C ambient temperature; total GDP-binding in BAT is elevated by 300%. GDP-binding remains unchanged during exposure to a long photoperiod.2.2. The increase of GDP-binding in response to a short day is less than 30% if compared to the increase induced by additional cold influence (outdoor/winter).3.3. GDP-binding in BAT, as a measure of the thermogenic capacity in BAT, is correlated to the NST capacity of the animals and the significance of BAT during NST is discussed.