Bombesin-induced hypothermia in the insulin-treated rat: effect on tail-skin temperature

Bombesin-like peptides are widely distributed in the mammalian central nervous system and appear to participate in the regulation of a variety of autonomic functions. Bombesin has been shown to alter feeding behavior, locomotor activity, and thermoregulation. Microinfusion of bombesin into the preoptic area of the hypothalamus produces a reduction in core body temperature, but only if the rat has been cold-exposed, food-deprived, or pretreated with insulin. The mechanism for bombesin-induced hypothermia under the latter two conditions is unknown. The present study evaluated the possible contribution of peripheral heat loss mechanisms in bombesin-induced hypothermia. Rats were administered insulin (10U/kg, Regular Iletin I i.m.) or saline followed by an intrahypothalamic injection of bombesin (.05 microgram/.25 microliter) or peptide vehicle. Rectal and tail-skin temperatures were measured continuously for 120 min. Changes in temperature were evaluated at 30, 60, 90, and 120 min., using analysis of variance. As previously demonstrated, bombesin produced hypothermia in rats pretreated with insulin. This reduction in core temperature was not associated with any significant alteration in tail-skin temperature. Results suggest that bombesin-induced hypothermia in rats pretreated with insulin may not be mediated by an increase in peripheral heat loss.