Features of adipocyte sensitivity to lipolytic agents in spontaneously hypertensive rats

Vasodilatation in response to heat, the role of tail vasodilatation in thermolysis and the ability of the animals to use free water for evaporative cooling were studied in control and capsaicin-desensitized rats.1) While vasodilatation in the tail began in the controls as soon as their temperatures reached 38.5–39°C, in most of the desensitized rats the onset of this reaction was above a body temperature of 40°C. 2) When exposed to 32°C, desalivated capsaicin-treated rats showed a significant hyperthermia as compared to the controls. If the tails were amputated too, the temperatures of the controls rose to near those of the desensitized animals. 3) In the case of prolonged heat exposure or at a higher ambient temperature (38°C), the desalivated tail-amputated controls still remained more tolerant to heat than the desensitized rats. 4) Even at an ambient temperature of 38°C, desalivated controls without tails exhibited excellent thermoregulation when a water bath was present; they used the free water for evaporation. Capsaicin-treated rats neglected the water bath, and their temperatures rose continuously. 5) The results suggest that capsaicin treatment impaired reflex vasodilatation to heat and the behaviour of using free water for heat dissipation.Supported by the Scientific Research Council, Ministry of Health, Hungary (4-05-0303-04-2-0) and MTA-OM-MEM-EÜM 70.211/79     

不同环境温度对精氨酸加压素引起的大鼠低温的影响及其与尾部散热变化的关系

 目的：探讨不同环境温度对精氨酸加压素（AVP）引起的大鼠低温及其与尾部散热变化的关系,以确定是否外周给予AVP能提高大鼠尾部散热反应。方法：实验用成年雄性SD大鼠,在3种不同环境温度（12 ℃、22 ℃和32 ℃）下,用无线遥测技术连续记录体核温度和尾部皮肤温度。上午10:00给大鼠腹腔注射AVP(10 μg/kg)或V1a受体阻断剂(30 μg/kg)。同时观察AVP或V1a受体阻断剂对大鼠背斜方肌微血管直径和理毛行为的影响。结果：(1)在3种不同环境温度中,AVP引起大鼠低温均伴有尾部皮肤温度降低反应。(2) V1a受体阻断剂能够阻断AVP引起低温和尾部皮肤温度降低效应。(3)AVP能明显引起背斜方肌微血管收缩反应。(4)AVP能提高大鼠的理毛行为(唾液理毛),而且这种作用也能被外周给予V1a受体阻断剂所阻断。(5)内源性AVP不参与正常大鼠尾部散热过程。结论：外周给予AVP引起大鼠低温,不是由于其降低了体温调定点,可能是由于其抑制了体温调节性产热和提高唾液理毛活动以增加体表蒸发散热所致。     

Autonomic thermoregulation after separation of the preoptic area from the hypothalamus in rats

To clarify the role of the hypothalamic preoptic area, in autonomic thermoregulation, the preoptic area (POA) of rats was disconnected from the rest of the brainstem by bilateral microknife cuts which spared or included the medial forebrain bundle. The animals' metabolic responses to exogenous norepinephrine (0.5 mg/kg, im) were then measured at ambient temperatures of 25° and 15°C. Oxygen uptake and colonic and tail skin temperatures were also measured at ambient temperatures of 34°, 25°, and 15° C. Finally, the febrile response to a challenge with liveSalmonella enteritidis was studied. Except for a slightly higher oxygen uptake at all ambient temperatures in the rats in which the medial forebrain bundle was cut, no differences were found in any of the variables studied between the POA-disconnected and the sham-operated animals. We conclude, therefore, that the POA is not essential for the integration of autonomic thermoregulatory responses in the rat.     

Goldblatt hypertension and operant thermoregulation in shaved, sialoadenectomized rats

The thermobehavioral consequences of angiotensinogenic two-kidney (2K) and sodium-volume dependent one-kidney (1K) forms of Goldblatt (one-clip) renovascular hypertension were assessed in shaved, sialoadenectomized rats. The 2K group (n = 8) underwent unilateral renal artery stenosis with the contralateral kidney left intact; whereas the Sham-Operation (Sham-Op) Control group (n = 7) received only a laparotomy. The 1K group (n = 8) underwent unilateral renal artery stenosis with contralateral nephrectomy, and the Uninephrectomy Control group (n = 6) was only unilaterally nephrectomized. Shaping and testing was conducted in a convective thermal controller that permitted the experimenters to control, through continuously reinforced bar-pressing, the ambient temperature during exposure to warm (37 degrees C) or cold (17 degrees C) temperatures. Testing at each temperature occurred over two 6-hr sessions with an interpolated 48-hr rest period. Both 2K and 1K hypertensive rats exhibited longer durations of heat escape than their appropriate normotensive controls across both testing sessions. No differences were detected in response frequency, duration of cold escape responding, or body temperature. The results suggest that either the increased vascular resistance or the neuroendocrine-sympathetic disorder linked to the pathogenesis of Goldblatt renovascular hypertension may promote heat retention or lower heat tolerance.     

The effects of two types of clothing on seasonal heat tolerance

The aim of this study was to look at changes in seasonal heat tolerance due to acclimatization produced by different types of clothing. A group of 12 female adults served as subjects in the study which lasted for 3 months from April to June during which the ambient temperature gradually rose. Of the group 6 of them (skirt group) wore knee-length skirts daily, and the others (trouser group) were dressed in full trousers during this acclimatization period. The heat tolerance before and after the acclimatization period was compared between the two groups under conditions in which relative humidity was 30% and ambient temperature was raised to 37°C. Rectal temperature, mean skin temperature and the loss of body mass caused by sweating were measured in the two groups. Before the acclimatization period, no significant differences were found between the two groups. However, observations after the acclimatization period showed higher rectal temperatures in control conditions (ambient air temperature 28°C, relative humidity 60%) in the skirt group. A lower increment of rectal temperature during heat exposure (ambient air temperature 37°C, relative humidity 30%) was also found in this group. Finally, the subjects in the skirt group lost less body mass due to sweating during heat exposure. Consequently, the overall index of physiological strain in the skirt group tended to show a lower value after the period of warm acclimatization. It was concluded that the subjects wearing knee-length skirts improved their heat tolerance with the advance of the seasons.     

The effects of long warm and cold ambient exposures on food intake water intake and body weight in the capsaicin desensitized rat

Seventeen Sprague Dawley rats received, subcutaneously, 250 mg·kg^–1 of capsaicin divided into 10 increasing doses (10–50 mg·kg^–1) and administered on 7 successive days. Nine controls were treated with an isotonic saline solution using the same protocol. The rats spent, in succession, 5 weeks at 20° C, 6 weeks at 33.5° C, 6 weeks at 8° C, 4 weeks at 30° C and, finally, 5 weeks at 20° C ambient temperature. Their mean food intake (FI), water intake (WI) and body weights were recorded daily. In the 2 groups of rats, FI was inversely related to ambient temperature. However, during the first few days of the exposures, FI in treated rats was greater than controls in the warm environment and less in the cold environment. In controls, WI increased linearly with ambient temperature in the warm environment. This relation was not found in treated rats: they drank less water than controls and lost body weight. During the first days at 8° C ambient temperature, rectal temperature decreased in treated rats and two animals died.The results are similar to those described for rats with hypothalamic lesions. They may also be related to a peripheral effect of the drug.This work was supported by the Centre National de la Recherche Scientifique (C.N.R.S. L.A. 181) and by the Institut National de la Santé et de la Recherche Médicale (I.N.S.E.R.M., A.T.P. 80-79-112)     

The effect of ambient temperature on rectal temperature,food intake and short term body weight in the capsaicin desensitized rat

1. .Subcutaneous injections of capsaicin (mean cumulative dose: 80.1±3.6 mg·kg^?1) permanently reduced the capacity of rats to withstand a hot environment when deprived of water. With water available, hyperthermia was discrete or absent in capsaicinized rats in hot environment.
2. Desensitization was followed by a significant decrease in both food intake and body weight. Treated rats recovered normal body weight after 3 weeks.
3. In a hot environment, compared to controls, food intake was significantly increased in capsaicin desensitized rats which maintained their body weight. In cold environment, food intake was decreased in capsaicin desensitized rats which lost body weight. At normal ambient temperature, food intake and body weight were similar in the 2 groups.
4. Caloric intake adjustment at high and at low temperatures was therefore disturbed in capsaicin desensitized rats. It is concluded that hypothalamic thermodetectors implicated in both thermoregulation and food intake behaviour could be partially damaged by capsaicin.

     

Hormone response of diabetic patients to exercise at cool and warm temperatures

Summary Both exercise and high ambient temperatures stimulate the secretion of counterregulatory hormones which can change glucose homeostasis. We studied whether in diabetic patients there are any differences in the hormonal response to exercise performed at cool or warm ambient temperatures. A study was performed on eight male insulin-dependent patients at rest and during exercise at + 10° C and + 30° C. Exercise consisted of three consecutive 15-min periods at 60% of maximal aerobic capacity. The concentrations of plasma lactate and counterregulatory hormones at rest were similar at warm and cool temperature, whereas prolactin concentration was higher (P < 0.01) at +30° C. Exercise resulted in an increase in noradrenaline, growth hormone and prolactin (P < 0.01), prevented the diurnal decrease in cortisol, but had no effect on glucagon. Hormone responses to exercise were similar at + 10° C and at +30°C, except for cortisol and noradrenaline which showed greater responses at warm than at cool temperatures. This may have been due to the higher relative work load at warm compared to cool temperatures as suggested by the higher heart rate and greater increase of lactate at +30° C. These data indicate that within a range of ambient temperatures commonly occurring in sports, the response of counterregulatory hormones is largely independent of ambient temperature in insulin-dependent diabetic patients.     

The effect of noradrenaline, injected into the hypothalamus, on thermoregulation in the cat.

1. Noradrenaline (NA) was microinjected into the anterior hypothalamic/preoptic area(AH/POA) of unanaesthetized cats held at ambient temperatures of 10, 22 or 35 degrees C. Loci in which injection of NA caused body temperature changes were also found to be sensitive to the febrile action of PGE1. 2. At all ambient temperatures, NA caused a dose-dependent fall in body temperature. However the mechanisms by which these temperature changes were brought about varied at different ambient temperatures. In cats maintained at the higher ambient temperature, NA activated heat loss mechanisms whereas in the cats maintained in the 10degrees C environment, the major effect of NA injection was an inhibition of heat conservation and heat production mechanisms. 3. We conclude that NA acts in cats not only as an inhibitor of heat conservation and production, but also acts in an excitatory manner on an active heat loss pathway within the AH/POA.     

Inhibition of diet-induced thermogenesis during pregnancy in the rat

Both virgin and pregnant rats were maintained at two different ambient temperatures (28° C and 10° C) for 19 days. Virgin rats maintained their daily food intake and body weight at both temperatures. At 28° C pregnant rats showed a greater daily food intake and body weight than virgin ones and their brown adipose tissue suffered regressive changes in composition when compared with brown fat of virgin rats. At 10° C the increases in daily food intake and body weight of pregnant rats took place from day 15–16 of pregnancy onward and foetuses taken from these pregnant rats were smaller than those taken from pregnant rats at 28° C. It is concluded that pregnant rats at thermoneutrality, although hyperphagic, do not show diet-induced thermogenesis. However, it is proposed that pregnant rats in the cold may show BAT cold-induced thermogenesis.     

Paramedian reticular nucleus: a thermolytic area in the rat medulla oblongata

The effects of stimulation or ablation of the paramedian reticular nucleus (PRN) of the rat medulla oblongata on the thermal responses induced by ambient temperature changes, a pyrogen, or a hypothermic substance were assessed. Electrical stimulation of the PRN elicited thermolytic reactions (including decreased metabolism, cutaneous vasodilation and hypothermia) which could be mimicked by micro-injection of kainic acid (an excitotoxic amino acid) into the same region. Bilateral electrolytic lesions in the PRN prevented the animals from responding to heat stress (35° C for 30 min) to some extent, but did not prevent responses to cold stress (4° C for 60 min). In addition, the thermogenic reactions induced by intrahypothalamic injection of polyriboinosinic acid: polyribocytidylic acid (a pyrogenic substance), or the thermolytic reactions induced by intraperitoneal administration of chlorpromazine (a tranquilizer), were antagonized respectively by activation or ablation of the PRN. This suggests that the PRN of the caudal medulla may function as a thermolytic area.     

Motilit?t und K?rpertemperatur von M?usen in verschiedenen Umgebungstemperaturen

Zusammenfassung 1. Es wurde untersucht, wie sich Motilität und Körpertemperatur von einzeln sitzenden Mäusen, die vorher unter normalen Laborbedingungen in Sammelkäfigen gehalten wurden, bei vorübergehendem Aufenthalt in Umgebungstemperaturen von 15, 20, 25, 30 und 35°C verändern.2. Die mittlere Körpertemperatur nach 21/2 stündigem Aufenthalt bei Umgebungstemperaturen von 15–25°C beträgt 36,6°C, sie steigt bei 35°C auf 38,8°C an.3. Die mittlere Bewegungshäufigkeit ist bei 25°C am kleinsten, sie steigt in kühlerer und wärmerer Umgebung an. Der prozentuale Anteil ruhig sitzender Mäuse nimmt mit steigender Umgebungstemperatur bis 25°C zu und fällt bei höheren Umgebungstemperaturen wieder ab.4. In allen Umgebungstemperaturen bestehen zwischen Bewegungshäufigkeit und Körpertemperatur lineare Beziehungen. Der Einfluß der Bewegungshäufigkeit auf die Körpertemperatur ist in kühler Umgebung größer als in der Wärme.

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Summary 1. Mice were kept single for 21/2 hours in ambient temperatures of 15, 20, 25, 30 und 35°C. It has been examined how motility and body temperature change under these circumstances.2. In an ambient temperature of 15–25°C the average body temperature was 36,6°C. It rose to 38,8°C at 35°C.3. The motor activity is minimal at 25°C. It rose at lower and higher ambient temperatures. The percentage of quiet mice increases with rising temperature up to 25°C, but decreases at ambient temperatures higher than 25°C.4. The relationship between motor activity and body temperature was linear at all ambient temperatures. The effect of motor activity on the body temperature was more pronounced in cool surroundings than in warm ones.

     

Salivary Secretion in the Rat in a Hot Environment

Conscious rats were found to secrete saliva from the submaxillary gland when exposed to heat. In rats with sympathetically denervated glands the secretory rate was a little lower and in parasympathetically denervated glands the secretion was almost abolished. The salivary flow appeared to increase with increasing ambient temperature and the secretion started earlier at higher temperatures. The secretion elicited by heat stress was compared to the secretion evoked by electrical stimulation of the parasympathetic nerve to the gland. It is concluded that the salivary secretion evoked by heat stress is mainly mediated by the parasympathetic secretory nerves, although the sympathetic fibres also take part.     

Rythmes circadiens des températures internes et ambiance thermique chez le rat

Résumé L'enregistrement chronique des températures cérébelleuses et sous-cutanées par thermistance a été réalisé chez le rat soumis à différentes températures ambiantes et à une alternance lumière-obscurité de 12 h (lumière de 7 à 19 h). La période du rythme des températures cérébelleuses et sous-cutanées est de 24 h avec acrophase nocturne (1 h) et amplitude de 0,75° C. L'amplitude et l'acrophase ne sont pas modifiées au cours des expositions à différentes températures ambiantes (20-25-30-34-35° C). Chaque augmentation d'ambiance se traduit par une élévation du niveau moyen de la température interne. Cette augmentation, peu perceptible entre 25 et 30° C, atteint 0,5° C entre 20 et 25° C et 1° C entre 30 et 34° C. Elle se maintient tout au long des 10 jours d'observation.Ces résultats soulèvent au moins 3 questions: le degré de liaison entre les rythmes d'activité (éveil) et de température, la labilité de la température interne qui varie avec l'ambiance alors que l'amplitude du rythme circadien reste constante, l'absence de diminution de la température interne après plusieurs jours en ambiance chaude alors qu'activité et métabolisme sont diminués dès le 2ème jour d'exposition.

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Circadian rhythms of rat internal temperatures and thermal ambiance

Summary Chronic recording of cerebellar and subcutaneous temperatures were carried out in rats maintained at different ambient temperatures in a 12 h light-dark cycle (light from 7 to 19 h). Cerebellar and subcutaneous temperatures followed a rhythm with a period of 24 h with acrophase at 1 h and an amplitude of 0.75° C. The amplitude and acrophase were not altered by modification of the ambient temperature (20-25-30-34 or 35° C), but each elevation of ambient temperature produced a rise in the mean internal temperature of the rat. This rise, hardly perceptible at ambient temperatures, of 25 and 30° C, reaches 0.5° C between 20 and 25° C and 1° C between 30 and 34° C. This elevation of temperature was maintained for the duration of the 10 days of observation.These results pose at least three questions: the degree of liaison between the rhythms of activity (waking) and temperature; the lability of the mean internal temperature, which alter with ambient temperature while the amplitude of the circadian rhythm is unaltered and the absence of reduction of mean internal temperature several days exposure to a raised ambient temperature, even when activity and metabolism are reduced by the second day of exposure.

     

A comparison of the effects of bilateral sections of the chorda tympani nerve and extirpation of the submaxillary and sublingual salivary glands on the eating and drinking patterns of the rat

The chorda tympani nerve (CT) innervates the fungiform papillae on the tip of the tongue and has been considered an important nerve for the sense of taste. The CT also contains the parasympathetic supply to the submaxillary and sublingual salivary glands. Therefore, changes in taste or feeding behavior following bilateral sections of CT are caused by both degeneration of fungiform papillae and the inevitable partial desalivation of the rat. In the present experiments we compared the effects of bilateral chorda tympani nerve sections with extirpation of submaxillary and sublingual glands on daily home cage eating and drinking patterns in the rat. Before and after surgery we analyzed the daily eating and drinking patterns, including such measures as intake, bout number, bout length, interbout interval and rate of consumption during bouts. The results of desalivation and bilateral CT sections were indistinguishable. The most profound change was that eating bout duration was increased following surgery. Since food intake did not increase, the results indicate a marked loss in eating efficiency over the daily ingestion periods. Although the eating patterns of desalivated and chorda tympani sectioned rats are quite similar, the evidence is not compelling that they have the same physiological basis. A second experiment was designed to test the hypothesis that the atypical eating patterns observed following bilateral sectioning of CT were the direct result of partial desalivation resulting from the denervation of the salivary glands. In this experiment a unilateral section was made of one CT and it was shown that the eating behavior was not affected. Then the contralateral submaxillary and sublingual salivary glands were removed. This resulted in a six-fold increase in feeding bout length. In all cases a unilateral CT section combined with extirpation of the contralateral salivary glands resulted in rats whose eating behavior was indistinguishable from the earlier data following either the bilateral CT sections or bilateral desalivations. The conclusion is drawn that the eating irregularities noted following bilateral CT sections result from this partial desalivation. CT sections were verified by taste bud counts in the fungiform papillae and histological examinations were made of salivary glands in rats receiving CT sections.     

Thermoregulatory effects of intraventricular injection of noradrenaline in the mouse and the influence of ambient temperature

1. At an ambient temperature of 20 degrees C, intraventricular injection of noradrenaline in the mouse resulted in hypothermia accompanied by a fall in metabolic rate and by cutaneous vasodilatation. Subcutaneous injection of noradrenaline resulted in hyperthermia with raised metabolic rate and cutaneous vasodilatation.2. The hypothermia and fall in oxygen consumption rate following intraventricular noradrenaline were prevented by pre-treatment with subcutaneous propranolol, while the cutaneous vasodilatation was un-affected. However, the effects of subcutaneously injected noradrenaline were completely abolished by subcutaneous propranolol. Intraventricular propranolol did not modify the hypothermic effect of intraventricular noradrenaline.3. The direction of the effect on body temperature of intraventricular noradrenaline was dependent upon ambient temperature; hypothermia occurring at low (15 degrees C) and hyperthermia at high (36 degrees C) ambient temperatures. However, when the possibility of any peripheral action of noradrenaline escaping into the systemic circulation was prevented by prior subcutaneous injection of propranolol, significant hypothermia could be detected at temperatures as high as 32 degrees C.4. The possibility that the effects of intraventricular noradrenaline could be due to complete abolition of central temperature regulation was further excluded by the occurrence of thermal salivation in all animals during experiments performed at 36 degrees C.5. It is suggested that, in the mouse, the hypothermic actions of intraventricular noradrenaline are due to a central effect, while its hyperthermic effects at high ambient temperature are due to escape of noradrenaline into the peripheral circulation. The hypothermia could be the result of selective activation of central heat loss mechanisms.6. Intraventricular noradrenaline was without effect on brain plasma-space although exposure to 100% oxygen caused a detectable fall.     

Thermal homeostasis in rats after intrahypothalamic injections of 6-hyroxydopamine.

Specific destruction of at least 90% of the noradrenergic neurons in the preoptic/anterior hypothalamic region (PO/AH) by local injection of 9-hyroxydopamine (6-HDA) did not disrupt thermoregulation by rats either in the heat or the cold. Examination of the multiple effector mechanisms suggested that thermal balance was maintained in a normal fashion, and that compensatory adjustments did not conceal individual dysfunctions. In contrast with the ineffectual 6-HDA lesions of the PO/AH were the outstanding impairments seen in rats following electrolytic lesions of this area. All the latter animals became severely hyperthermic during the 1st h of exposure to an ambient temperature of 40 degrees C, and half of them were additionally unable to maintain body temperatures when exposed to an ambient temperature of 6 degrees C. The electrolytic lesions reduced norepinephrine levels in the PO/AH, but the 50-70% depletions were substantially smaller than those found in 6-HDA-treated rats. These results raise new doubts about whether central noradrenergic fibers have an important role in the regulation of body temperature by rats.     

Impaired thermoregulation against cold in capsaicin pretreated rats

A study was made of the effects of pretreatment with fractionated capsaicin on the changes in body temperature (Tb) induced in rats by exposure to cold and to warm environments, and by administration of histamine (40 mg X kg-1) or of pentobarbital (20 mg X kg-1). At the ambient temperature of 22 degrees C the Tb of capsaicin pretreated rats was lower than that of rats treated only with solvent (p less than 0.001). The capsaicin pretreated rats showed impairment of thermoregulation at both high and low environmental temperatures: their Tb rose to a higher level in a warm environment, while in a cold environment their Tb was lower than that of the control rats. Histamine and pentobarbital caused larger drops in the Tb of capsaicin pretreated rats than in the controls. These findings challenge the concept that capsaicin treatment acts exclusively on thermoregulatory mechanisms concerned with warmth sensation.     

Interactions of behavioral and autonomic thermoregulation in heart stressed pigeons

The interactions of behavioral and autonomic thermoregulation in pigeons during ambient heat load were studied by simultaneous measurements of instrumental response rate for cold air reinforcement and respiratory rate. When providing sufficient reinforcement-magnitudes, deep body temperatures were stabilized, due to a linear increase of response rate with ambient loads from 40–60° C, without involving an increase in respiratory heat dissipation. This was effected by maintaining the temporal mean of air temperature and consequently of all skin temperatures at a level independent from load temperature (Fig. 3). When the efficiency of instrumental thermoregulation was limited by reducing the reinforcement-magnitude, not only the instrumental response rate increased, but in addition body temperatures and subsequently respiratory rate rose with the thermal load. Thus a positive correlation between body temperatures and response rate and a simultaneous increase of autonomic heat defence activities characterize incomplete behavioral thermoregulation. The instrumental response rate rapidly followed changes of external load temperature without preceding changes of core temperatures or skin temperatures at well feathered areas (Fig. 6). These findings suggest that the input signal controlling instrumental thermoregulatory behavior is related to the rate of change of temperatures at exposed areas of the body shell, whereas the autonomic heat defence response follows the steady displacements of body temperatures. This points to an important difference between the input signals controlling behavioral and autonomic heat defence in the pigeon.     

Thermoregulatory behaviour after repetitive cooling of the preoptic area and of the spinal cord in the rat

Summary The thermoregulatory behaviour of 6 rats was studied during exposure to cold and warm ambient temperatures after either the preoptic area or the cervical spinal cord had been intermittently cooled for an average of 130 h. The precooled animals worked more for heat in cold environments and less for cool air in a warm environment than the control animals. This behaviour, probably due to a decreased ability of the precooled animals to retain heat, suggests that the precooled animals were not fully adapted to cold.