[Role of oxotremorine in arginine vasopressin-induced hypothermia and its effects on behavioral thermoregulatory response in rats].

OBJECTIVE: To investigate the role of oxotremorine in arginine vasopressin (AVP)-induced hypothermia and its effects on the behavioral thermoregulatory response. METHODS: Core temperature (Tc), brown adipose tissue (BAT) temperature and motor activities were monitored in undisturbed female SD rats using radiotelemetry. The behavioral thermoregulatory response was monitored in rats using radiotelemetric temperature gradient apparatus. Effect of AVP (10 microg/kg) and oxotremorine (0.25 mg/kg) on Tc, motor activities, BAT temperature (T(BAT)), grooming activities and the behavioral thermoregulatory response were observed in rats. RESULTS: Administration of AVP and oxotremorine caused a significant drop in Tc, T(BAT), and an increases in grooming activities, respectively. The hypothermic responses were accompanied with a preference for cooler ambient temperature. Oxotremorine augmented the reduction of Tc, T(BAT), and the elevation of grooming activities resulting from AVP, and lasting a longer time. Administration of oxotremorine followed immediately by AVP injection in rats was also shown to induce a preference for cooler ambient temperature, but there was no significant difference compared with AVP. CONCLUSION: AVP-induced hypothermia was related with the set point temperature reduction, inhibiton of BAT thermogenesis and an increases in grooming activities. Oxotremorine could participate in peripheral AVP-induced hypothermia by affecting BAT thermogenesis and behavioral thermoregulation.

[Simultaneous telemetric analyzing of the temporal relationship for the changes of the circadian rhythms of brown adipose tissue thermogenesis and core temperature in the rat].

OBJECTIVE: To measure simultaneously the time course for the circadian rhythm of brown adipose tissue(BAT) thermogenesis and core temperature, and analyzing their temporal relationship. METHODS: The circadian rhythm of core temperature (Tc), BAT temperature (T(BAT)), axillary temperature (Tax) and motor activity were simultaneously measured by telemetry in adult male Sprague-Dawley rats at an ambient temperature of 22 degrees C during a 12-h light:12-h dark photoperiod (lights on at 06:00 h and lights off at 18:00 h). RESULTS: (1) T(BAT) was 0.67 degrees C lower than Tc group under the light phase, but it was similar to that Tc during the dark phase. The rate of increase in T(BAT) was higher than corresponding increases in Tc at the start of transition from the light to dark phase, and increase in T(BAT) commenced approximately 8 min before Tc increases. Whereas at the start of transition from the dark to light phase, decrease in T(BAT) commenced approximately 4 min before Tc decreases. (2) The amplitude of the circadian Tax rhythm was similar to that of Tc. During either the light phase or dark phase, Tax was lower than simultaneous measurement of Tc. (3) Increases in behavioral activity commenced before increases in T(BAT) and Tc at the start of transition from the light to dark phase. CONCLUSION: BAT thermogenesis contributes to increase in core temperature during the dark phase, indicating that circadian changes of BAT thermogenesis does indeed play significant role in the overall maintenance of the circadian rhythm of core temperature.

Physostigmine-induced hypothermic response in rats and its relationship with endogenous arginine vasopressin.

AIMS: It is well known that physostigmine (PHY) and other anticholinesterase (anti-ChE) agents induce hypothermia in rodents but little is known about the mechanism of action. Because arginine vasopressin (AVP) has been found to be an endogenous antipyretic molecule in the CNS, we determined if PHY-induced hypothermia is linked to the endogenous release of AVP. MAIN METHODS: Core temperature and motor activity were monitored by telemetry in rats maintained at an ambient temperature of 25 degrees C. Tail skin temperature was also measured at 30min intervals to estimate nonevaporative heat loss. The central cholinergic antagonist, scopolamine (1mg/kg; ip) and an AVP V(1) receptor antagonist (30microg/kg; ip) were administered during the period of PHY (200microg/kg; sc) induced hypothermia at 10am. Plasma AVP concentration and plasma cholinesterase (ChE) activity were measured at 50min after administration of PHY or scopolamine, respectively. KEY FINDINGS: PHY led to a rapid reduction in core temperature concomitant with a marked increase in heat loss from the tail. The hypothermic response of PHY was blocked by the AVP V(1) receptor antagonist. Administration of scopolamine also reversed the hypothermic responses and led to marked elevations in motor activity. Plasma AVP levels increased markedly at 50min after PHY and plasma ChE activity was significantly reduced by PHY. SIGNIFICANCE: The results clearly demonstrate that PHY-induced hypothermia was blocked by the AVP V(1) antagonist and associated with elevations in plasma AVP, suggesting a novel role for AVP in the mechanism of action of anti-ChE agents.