Autonomic and behavioural thermoregulation in starved rats

1. We investigated the mechanism of starvation-induced hypothermia in rats. 2. Threshold core temperatures (T-cor) for tail skin vasodilatation and col d-induced thermogenesis were determined after a 3 day starvation using a ch ronically implanted intravenous thermode. Food deprivation significantly lo wered the threshold T-cor for heat production, but did not affect the heat loss threshold. 3. Thermogenic response to a fall in T-cor below its thresh old was enhanced by starvation. 4. Preferred ambient temperatures (T-pref) and T-cor were measured before a nd during a 3 day starvation in a thermal gradient. The 3 day starvation si gnificantly lowered T-cor only in the light phase of the day. The level of hypothermia was the same throughout the fasting period, while T-pref gradua lly increased during the 3 days of starvation. 5. When rats were starved at a constant ambient temperature of 25 degrees C (no thermal gradient), their T-cor levels were comparable with those of th e rats kept in the thermal gradient. 6. The results suggest that, in rats, hypothermia caused by starvation ws n ot due to a decrement in thermogenic capability, but was due to a decrease in the threshold for the activation of thermogenesis.