Role of endogenous arginine vasopressin in tonic thermoregulatory processes in rats during the light phase

AIM: To determine the role of endogenous arginine vasopressin (AVP) in tonic thermoregulatory processes in rats during the light phase. METHODS: The core temperature (Tc) and temperature in brown adipose tissue (BAT) were simultaneously measured by telemetry in adult male Sprague-Dawley rats at an ambient temperature of 22 °C during a 12-h light/12-h dark photoperiod. At 10:00,the rats were intraperitoneally injected with V_1a vasopressin receptor antagonist (30 μg/kg) or AVP (10 μg/kg). Plasma AVP concentration was measured by an enzyme-linked immunosorbant assay during the light phase and dark phase. Serum triglyceride, free fatty acid and glycerol were measured 60 min after AVP treatment. Grooming activities were also observed at 10-min intervals after AVP treatment. RESULTS: V_1a vasopressin receptor antagonist elevated the Tc and BAT temperature during the light period. The plasma AVP level was significantly elevated when Tc and BAT temperature decreased during the light phase. Intraperitoneal injection of AVP elicited rapid drop in Tc concomitant with a marked decrease in BAT temperature, and also increased grooming behavior in the rats. Intraperitoneal injection of AVP produced a decrease in serum free fatty acid and glycerol, and an increase in serum triglyceride. CONCLUSION: Endogenous AVP, acting through V_1a vasopressin receptor, is involved in tonic thermoregulatory processes in male rats during the light phase because plasma AVP concentration is higher during light period than that during dark period, and V_1a vasopressin receptor antagonist elevates the Tc and BAT temperature. AVP decreases BAT temperature, serum free fatty acid and glycerol, and increases grooming behavior, suggesting that the mechanism of AVP-induced hypothermia is involved in suppression of lipolysis, decrease in BAT thermogenesis and increase in heat loss.