Gradual cold acclimation induces cardioprotection without affecting ß-adrenergic receptor-mediated adenylyl cyclase signaling.

Novel strategies are needed that can stimulate endogenous signaling pathways to protect the heart from myocardial infarction. The present study tested the hypothesis that appropriate regimen of cold acclimation (CA) may provide a promising approach for improving myocardial resistance to ischemia/reperfusion (I/R) injury without negative side effects. We evaluated myocardial I/R injury, mitochondrial swelling, and ß-adrenergic receptor (ß-AR)-adenylyl cyclase-mediated signaling. Male Wistar rats were exposed to CA (8°C, 8 h/day for a week, followed by 4 wk at 8°C for 24 h/day), while the recovery group (CAR) was kept at 24°C for an additional 2 wk. The myocardial infarction induced by coronary occlusion for 20 min followed by 3-h reperfusion was reduced from 56% in controls to 30% and 23% after CA and CAR, respectively. In line, the rate of mitochondrial swelling at 200 µM Ca2+ was decreased in both groups. Acute administration of metoprolol decreased infarction in control group and did not affect the CA-elicited cardiprotection. Accordingly, neither ß1-AR-Gsα-adenylyl cyclase signaling, stimulated with specific ligands, nor p-PKA/PKA ratios were affected after CA or CAR. Importantly, Western blot and immunofluorescence analyses revealed ß2- and ß3-AR protein enrichment in membranes in both experimental groups. We conclude that gradual cold acclimation results in a persisting increase of myocardial resistance to I/R injury without hypertension and hypertrophy. The cardioprotective phenotype is associated with unaltered adenylyl cyclase signaling and increased mitochondrial resistance to Ca2+-overload. The potential role of upregulated ß2/ß3-AR pathways remains to be elucidated.NEW & NOTEWORTHY We present a new model of mild gradual cold acclimation increasing tolerance to myocardial ischemia/reperfusion injury without hypertension and hypertrophy. Cardioprotective phenotype is accompanied by unaltered adenylyl cyclase signaling and increased mitochondrial resistance to Ca2+-overload. The potential role of upregulated ß2/ß3-adrenoreceptor activation is considered. These findings may stimulate the development of novel preventive and therapeutic strategies against myocardial ischemia/reperfusion injury.

Could human cold adaptation decrease the risk of cardiovascular disease?

The impact of repeated exposure to cold and cold adaptation on human cardiovascular health is not fully understood. The aim of the study was to determine the effect of cold adaptation on cardiovascular risk factors, thyroid hormones and the capacity of humans to reset the damaging effect of oxidative stress. Ten well cold-adapted winter swimmers (CA) and 16 non-adapted controls (CON) were enroled in this experiment to test whether cold adaptation could influence the parameters of lipoprotein metabolism, cholesterol efflux capacity (CEC), homocysteine, thyroid hormones, antioxidant defence markers (reduced glutathione (GSH), glutathione peroxidase 1 (GPX1), glutathione reductase (GR), catalase (CAT) and paraoxonase 1 (PON1)) and oxidative stress markers (concentration of conjugated dienes (CD)). A decreased apolipoprotein B/apolipoprotein A1 (ApoB/ApoA1) ratio was found in the CA group (p<0.05), but other lipoprotein parameters, including CEC, did not differ significantly. Plasma homocysteine was lower in CA subjects in comparison with controls (p<0.05). Higher triiodothyronine (T3) values were observed in the CA compared to the CON (p<0.05) group, but TSH and other thyroid hormones did not differ between both groups. CA subjects had lower activity of GPX1 (p<0.05), lower concentrations of CD (p<0.05) and increased activities of PON1 (p<0.001) compared to CON subjects. A trend for decreased activity of CAT (p=0.06) in CA compared to CON groups was also observed, but GSH levels did not differ significantly. Zn concentration was higher in the CA group than in the CON group (p<0.001). Human cold adaptation can influence oxidative stress markers. Trends towards the improvement of cardiovascular risk factors in cold-adapted subjects also indicate the positive effect of cold adaptation on cardio-protective mechanisms.

Changes of plasma obestatin, ghrelin and NPY in anorexia and bulimia nervosa patients before and after a high-carbohydrate breakfast.

Peptides ghrelin, obestatin and neuropeptide Y (NPY) play an important role in regulation of energy homeostasis, the imbalance of which is associated with eating disorders anorexia (AN) and bulimia nervosa (BN). The changes in ghrelin, obestatin and NPY plasma levels were investigated in AN and BN patients after administration of a high-carbohydrate breakfast (1604 kJ). Eight AN women (aged 25.4+/-1.9, BMI: 15.8+/-0.5), thirteen BN women (aged 22.0+/-1.05, BMI: 20.1+/-0.41) and eleven healthy women (aged 25.1+/-1.16, BMI: 20.9+/-0.40) were recruited for the study. We demonstrated increased fasting ghrelin in AN, but not in BN patients, while fasting obestatin and NPY were increased in both AN and BN patients compared to the controls. Administration of high-carbohydrate breakfast induced a similar relative decrease in ghrelin and obestatin plasma levels in all groups, while NPY remained increased in postprandial period in both patient groups. Ghrelin/obestatin ratio was lower in AN and BN compared to the controls. In conclusions, increased plasma levels of fasting NPY and its unchanged levels after breakfast indicate that NPY is an important marker of eating disorders AN and BN. Different fasting ghrelin and obestatin levels in AN and BN could demonstrate their diverse functions in appetite and eating suppression.

Thermal, cardiac and adrenergic responses to repeated local cooling.

The aim of this study was to ascertain whether repeated local cooling induces the same or different adaptational responses as repeated whole body cooling. Repeated cooling of the legs (immersion into 12 degrees C water up to the knees for 30 min, 20 times during 4 weeks = local cold adaptation - LCA) attenuated the initial increase in heart rate and blood pressure currently observed in control subjects immersed in cold water up to the knees. After LCA the initial skin temperature decrease tended to be lower, indicating reduced vasoconstriction. Heart rate and systolic blood pressure appeared to be generally lower during rest and during the time course of cooling in LCA humans, when compared to controls. All these changes seem to indicate attenuation of the sympathetic tone. In contrast, the sustained skin temperature in different areas of the body (finger, palm, forearm, thigh, chest) appeared to be generally lower in LCA subjects than in controls (except for temperatures on the forehead). Plasma levels of catecholamines (measured 20 and 40 min after the onset of cooling) were also not influenced by local cold adaptation. Locally cold adapted subjects, when exposed to whole body cold water immersion test, showed no change in the threshold temperature for induction of cold thermogenesis. This indicates that the hypothermic type of cold adaptation, typically occurring after systemic cold adaptation, does not appear after local cold adaptation of the intensity used. It is concluded that in humans the cold adaptation due to repeated local cooling of legs induces different physiological changes than systemic cold adaptation.

Basal and exercise-induced sympathetic nervous activity and lipolysis in adipose tissue of patients with anorexia nervosa.

BACKGROUND: The sympathetic nervous system plays an important role in the regulation of adipose tissue (AT) lipolysis, which is a key step in the metabolic processes leading to the decrease of fat mass. The present study was designed to determine in vivo basal and exercise-stimulated lipolysis and concentrations of catecholamines, the major hormones controlling lipolysis, in subcutaneous abdominal AT in patients with anorexia nervosa (AN), characterized by self-induced starvation and excessive exercises resulting in severe malnutrition and fat store loss. The results of local catecholamines and glycerol levels were compared with those in plasma in both experimental groups. MATERIAL AND METHODS: An in vivo microdialysis technique was used for the assessment of norepinephrine, dihydroxyphenylalanine, dihydroxyphenylacetic acid and glycerol concentrations in subcutaneous AT of 10 women with AN (body mass index: 15.57 +/- 0.55 kg m(-2)) and 10 age-matched controls (body mass index: 21.56 +/- 0.41 kg m(-2)). Both the AN patients and the control subjects underwent a 1.5 W kg(-1) exercise test. RESULTS: Basal AT norepinephrine concentrations were increased in the AN patients in comparison with the controls. Basal AT glycerol concentrations were similar in both groups. During exercise, a local increase in the AT norepinephrine and glycerol concentrations was observed in the AN patients only. In contrast to the controls, the basal AT dihydroxyphenylalanine and dihydroxyphenylacetic acid levels in the AN patients were high and remained unchanged during exercise. Basal and exercise-stimulated plasma norepinephrine, dihydroxyphenylalanine, dihydroxyphenylacetic acid and glycerol levels were not different in the AN patients and healthy controls. CONCLUSION: Our study provides evidence of elevated baseline and exercise-induced sympathetic nervous activity and exercise-induced lipolysis in abdominal AT of AN patients.

Role of beta adrenoceptors in metabolic and cardiovascular responses of cold exposed humans.

Effect of a nonspecific beta adrenergic blocker - propranolol (40 mg per os) on thermoregulatory responses of cold water immersed (12.5 degrees C) humans was studied. Propranolol attenuates resting and cold induced thermogenesis, rectal temperature, heart rate and systolic blood pressure, but increases production of adrenaline and cortisol. Propranolol has no effect on the threshold body temperature for induction of cold thermogenesis and on central thermosensitivity. The following conclusions are drawn from consideration of the data presented: During the early phase of cooling (20 min after the start of cooling) the thermogenesis mediated by beta adrenergic receptors may cover about 80% of the total metabolic increase induced by cold. After about 30 min of cooling the relative proportion of beta adrenergic thermogenesis starts to decline, reaching 20% of the total cold thermogenesis at the end of cooling.It can be suggested from consideration of the data that, in man, the beta adrenergic receptors in the heart, blood vessels, adipocytes and muscles participate in mediating effect of cold on cardiovascular and thermoregulatory responses. Furthermore, these data imply that human adrenergic thermogenesis is produced outside of the brown adipose tissue. Thus, physiological mechanisms mediating adrenergic thermogenesis in humans appear to be different from those in small mammals.

Thermoregulation in winter swimmers and physiological significance of human catecholamine thermogenesis.

Thermoregulation in control subjects and cold-adapted winter swimmers was examined during 1 h of cold water immersion (13 C). It was found that the thermoregulatory functions of winter swimmers differ from those of non-cold-adapted subjects. As evident from the relationship between rectal temperature and the magnitude of cold thermogenesis, in controls a significant part of cold thermogenesis during the early phase of cooling was induced by changes in peripheral temperature input, while in the late phase of cooling it was the central temperature input which was mainly engaged in induction of cold thermogenesis. In winter swimmers the magnitude of cold thermogenesis was solely related to changes in rectal temperature, indicating the predominance of the central temperature input in activation of heat production mechanisms. The thermoregulatory threshold for induction of cold thermogenesis was lowered (by 0.34 C), but the apparent hypothalamic thermosensitivity was the same as in non-cold-adapted subjects. These differences are indicative of adaptation of thermoregulatory control centres. Additionally, the activity of thermoregulatory effectors was also changed. Shivering was induced later during cooling (after 40 min) in winter swimmers than in controls, which suggests an important participation of non-shivering thermogenesis in the early thermogenic response. Winter swimmers also showed bradycardia and a greater reduction in plasma volume during cooling. The data indirectly indicate restriction of heat loss from the body. Only a non-significant increase in quantity of subcutaneous fat was observed in winter swimmers. Thus, winter swimmers were able to survive a significantly greater temperature gradient between body and environment than non-cold-adapted subjects by modifying the sensory functions of hypothalamic thermoregulatory centres to lower heat loss and produce less heat during cold exposure. Additionally, the capacity of the total cold thermogenesis due to potentiation of non-shivering heat production was also increased. Heat produced due to thermogenic action of adrenaline may represent more than a quarter of the total cold thermogenesis. In conclusion, the data suggest that winter swimmers exhibit metabolic, hypothermic and insulative types of cold adaptation.

Human physiological responses to immersion into water of different temperatures.

To differentiate between the effect of cold and hydrostatic pressure on hormone and cardiovascular functions of man, a group of young men was examined during 1-h head-out immersions in water of different temperatures (32 degrees C, 20 degrees C and 14 degrees C). Immersion in water at 32 degrees C did not change rectal temperature and metabolic rate, but lowered heart rate (by 15%) and systolic and diastolic blood pressures (by 11 %, or 12%, respectively), compared to controls at ambient air temperature. Plasma renin activity, plasma cortisol and aldosterone concentrations were also lowered (by 46%, 34%, and 17%, respectively), while diuresis was increased by 107%. Immersion at 20 degrees C induced a similar decrease in plasma renin activity, heart rate and systolic and diastolic blood pressures as immersion at thermoneutrality, in spite of lowered rectal temperature and an increased metabolic rate by 93%. Plasma cortisol concentrations tended to decrease, while plasma aldosterone concentration was unchanged. Diuresis was increased by 89%. No significant differences in changes in diuresis, plasma renin activity and aldosterone concentration compared to subjects immersed to 32 degrees C were observed. Cold water immersion (14 degrees C) lowered rectal temperature and increased metabolic rate (by 350%), heart rate and systolic and diastolic blood pressure (by 5%, 7%, and 8%, respectively). Plasma noradrenaline and dopamine concentrations were increased by 530% and by 250% respectively, while diuresis increased by 163% (more than at 32 degrees C). Plasma aldosterone concentrations increased by 23%. Plasma renin activity was reduced as during immersion in water at the highest temperature. Cortisol concentrations tended to decrease. Plasma adrenaline concentrations remained unchanged. Changes in plasma renin activity were not related to changes in aldosterone concentrations. Immersion in water of different temperatures did not increase blood concentrations of cortisol. There was no correlation between changes in rectal temperature and changes in hormone production. Our data supported the hypothesis that physiological changes induced by water immersion are mediated by humoral control mechanisms, while responses induced by cold are mainly due to increased activity of the sympathetic nervous system.

Hibernation triggers and cryogens: do they play a role in hibernation?

A survey of the literary evidence on cryogens and hibernation induction triggers is given and the results of experiments on the effect of hypothalamic or i.v. injections of opioids and plasma from hibernating European hamsters on body temperature control of rabbits are presented. Pharmacological doses of a delta opioid--DADLE (25 or 50 micrograms), when injected into the anterior hypothalamus, induce a small and short-lasting hypothermic effect in cold exposed rabbits, due to the downward shift of the temperature threshold for shivering. Lower doses (5 micrograms) are without effect, similarly as i.v. administrations (500 micrograms/kg) of this substance. Intrahypothalamic injections of met-enkephalin (0.1-1 microgram) induce a slight hyperthermia due to the shift of all thermoregulatory effectors to higher body temperatures. Intrahypothalamic injections of plasma from hibernating European hamsters do not influence the body temperature control in rabbits.

Production of systemic and hypothalamic cytokines during the early phase of endotoxin fever.

Changes in concentrations of cytokines in plasma and in hypothalamic push-pull perfusates of guinea pigs were measured within the 1st hour after intramuscular injections of bacterial lipopolysaccharide (LPS; Escherichia coli, 20 micrograms/kg) or solvent (0.9% saline). In control animals injected with solvent, interleukin (IL)-1 and tumor necrosis factor alpha (TNF-alpha) were not detectable in plasma. Only IL-6 was present in picogram quantities. Within 45 min after injection of LPS, the concentrations of IL-1, TNF-alpha, and IL-6 increased in the plasma: by several orders of magnitude for TNF-alpha and about tenfold for IL-G. Picogram amounts of biologically active IL-1 were detected in plasma after injection of LPS. No steady state levels of systemic cytokines were reached during the experimental period. In hypothalamic perfusates of animals injected with the solvent, no IL-1 was detectable. TNF-alpha could be detected at higher concentrations than IL-6. IL-6 was detectable at tenfold lower concentrations than in the plasma. In animals injected with LPS, the hypothalamic concentration of IL-6 started to increase during the period 15-30 min and the concentrations of TNF-alpha during the period 30-45 min after LPS injection. The concentrations of IL-6 increased by 300-400% and did not exceed picogram values. No progressive increase of hypothalamic levels of these cytokines was observed during the time course of the experiment. The method used did not detect any changes in the amount of biologically active IL-1 in hypothalamic perfusates of LPS-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Can haloperidol disguise fever?

Haloperidol when applied intraperitoneally to cold-exposed febrile rabbits induces a strong hypothermic effect. This effect is due to the downward shift of the threshold central temperature for induction of cold thermogenesis and vasomotion. The shift occurs during the early phase of the fever and is less prominent during the late phase of the fever. The hypothermic effect of high doses of haloperidol can eliminate the increase of body temperature in febrile individuals.

The role of dopaminergic pathways in thermoregulation in the rabbit.

Dopamine, when injected into the anterior hypothalamus of the rabbit, induced a slight hyperthermia due to an upward shift of the threshold central temperature for induction of cold thermogenesis, panting and vasodilation. A slightly reduced thermosensitivity of the controller regulating vasodilation may also contribute to the hyperthermic effect of dopamine. Intrahypothalamic injections of the dopamine agonist, apomorphine, induced a similar effect to that of dopamine, with the exception that the thermosensitivity of the controller regulating vasodilation was not changed. Intraperitoneal injections of a dopamine antagonist, haloperidol, induced a marked hypothermia, due to a downward shift of the threshold central temperature for induction of cold thermogenesis, panting and vasodilation. A slightly reduced thermosensitivity of the controller regulating vasodilation was also observed. Intrahypothalamic injections of haloperidol did not induce an antagonist effect to dopamine, but rather tended to induce hyperthermia. Thermoregulatory responses, occurring after administration of dopamine or apomorphine, partially resembled those seen after administration of neurotensin or prostaglandins.

Mode of ACTH antipyretic action.

The method of intestinal cooling was used to analyze the effect of centrally administered ACTH in microgram quantities on hypothalamic centers regulating activity of thermoregulatory outputs (cold thermogenesis--CT, peripheral vasomotor tone--PVMT, respiratory evaporative heat loss--REHL). ACTH, when injected into the supraoptic area of the anterior hypothalamus of normal rabbits, had no significant effect on body temperature control. Intrahypothalamic administration of ACTH during the early phase of the fever, induced by intravenous injection of exogenous pyrogen, evoked dissociation of temperature thresholds for cold and warm defence, shifting the threshold for induction of cold thermogenesis to lower central temperatures. The thermosensitivity of centers controlling cold thermogenesis was lowered and the maximal values of cold thermogenesis were depressed to about 30% of those in control rabbits. Central administration of ACTH in the late phase of the fever (120 min after IV injection of endotoxin) induced a smaller effect than in the early phase of the fever--the downward shift of the temperature threshold for cold thermogenesis was less evident and the thermosensitivity of the controller remained unchanged. The changes in activity of thermoregulatory centers that occurred after ACTH in febrile rabbits correspond to those observed in the late phase of the fever in ACTH-untreated rabbits. It is suggested therefore, that the presumed increase in ACTH production during fever might represent a negative feed-back mechanism contributing to the termination of the febrile state.

Changes in metabolism, food and water intake of C3H mice following transplantation of Gardner lymphosarcoma (LSG).

Mice bearing progressing Gardner lymphosarcoma (LSG) increasingly gained in weight in the course of LSG development but their food and water consumption was reduced in comparison with control animals. During the neoplastic growth, oxygen consumption was decreased and the proportion of the metabolically active part (i.e. dried matter) declined. The body weight of tumour-bearing mice successfully cured with methotrexate (MTX) (30 mg/kg body weight, administered on days 1 and 3) was substantially lower than those of non-treated tumourous animals and was similar to that of intact controls. The food and water consumption of mice treated with MTX and that of control animals was similar. Values of the metabolic rate observed in animals treated with MTX were comparable to those recorded in the control group.

Thermoregulation of the rabbit during the late phase of endotoxin fever.

In the late phase of the fever occurring 120 or more min after i.v. injection of endotoxin (1 microgram/kg) to female rabbits, marked shifts of thresholds for respiratory evaporative heat loss and for peripheral vasodilatation to higher body core temperatures were observed. In contrast, the threshold body core temperature for cold thermogenesis was shifted downwards. As a result, the interthreshold zone was widened. Within the body temperature range of 37.4 to 39.9 degrees C neither heat production or heat loss mechanisms were operant and the body temperature was determined mainly by passive heat transfer between the body and the environment. Outside this zone, the sensitivities of the heat and cold defence activities to changes in body core temperature appeared to be unchanged.

Effect of bombesin on thermoregulation of the rabbit.

Injections of bombesin (BOM, 125, 250 and 500 ng) into the preoptic/anterior hypothalamus caused dose-related decreases of threshold temperatures for metabolic cold defence, cutaneous vasomotor tone and respiratory rate, combined with a reduced sensitivity of these thermoregulatory effectors in response to core temperature changes induced at thermoneutral or warm ambient conditions. Intracisternal (i.c.) injections of BOM (250 ng) produced qualitatively identical thermoregulatory effector changes in response to core temperature changes. Injections of BOM into the posterior hypothalamus did not affect body temperature control. Increased locomotor behavior, licking and grooming was elicited, however, from all injection sites. The results explain the prevailing hypothermic effect of BOM as the consequence of the concerted decrease in threshold temperatures and "gains" of all autonomic thermoregulatory effectors and suggest the activation of warm inputs, relative to cold inputs, at the hypothalamic level as the underlying mechanism. Direct or indirect inhibition of the intrinsic hypothalamic system involving thyrotropin-releasing hormone (TRH) and consequent deactivation of central noradrenergic pathways known to generate the entire autonomic pattern of cold defence might be involved in the neuro-humoral changes resulting in hypothermic effects of centrally applicated BOM.

Hyperthermic effect of neurotensin in the rabbit.

Neurotensin injected into the anterior hypothalamus of the rabbit induces a consistent upward shift of the threshold core temperatures for inducing cold thermogenesis, peripheral vasomotor tone and respiratory evaporative heat loss, while leaving the efficiency and the intensity of these thermoregulatory outputs unchanged. Neurotensin injections into the PH are without effect on body temperature control. The effect of neurotensin is interpreted as a selective inhibition of activity of warm sensors in the anterior hypothalamus. The possible mediating role of dopaminergic pathways in the neurotensin action is discussed.