Centrally administered thyrotropin-releasing hormone in the regulation of regional blood flow to brown adipose tissue in rats.

The effects of thyrotropin-releasing hormone (TRH) administered via the lateral ventricle on the blood flow to the interscapular brown adipose tissue (IBAT) was studied in urethane anaesthetized rats. TRH in i.c.v. doses of 50 or 5 micrograms/kg produced a significant and transient decrease in IBAT blood flow. The effect of 5 micrograms/kg TRH was blocked by bilateral surgical denervation. TRH caused a comparable decrease in blood flow to both the innervated pad of unilaterally denervated rats and the intact pads of non-operated rats whereas no response to TRH was observed in the denervated pad. Adrenal demedullation partly inhibited but did not completely abolish the effect of TRH on IBAT blood flow and lessened the increase in serum adrenaline caused by TRH. The effect of TRH was dose dependently suppressed by pretreatment with prazosin 15 min prior to TRH. Yohimbine did not influence the effect of TRH on IBAT blood flow. Central administration of TRH affects the regional blood flow to IBAT and appears to interfere with neural mechanisms that involve mediation by the alpha 1-adrenoceptors on the vasculature. The effect is in part due to circulating adrenaline from the adrenal medulla.