Depletion of noradrenaline in the hypothalamus reduces the febrile responses induced by prostaglandin E2, thyrotropin-releasing hormone and beta-endorphin in rats.

The effects of pretreatment of rats with an intrahypothalamic injection of 6-hydroxydopamine on the thermal responses induced by intrahypothalamic injection of noradrenaline, prostaglandin E2, thyrotropin-releasing hormone or beta-endorphin were assessed. Administration of either noradrenaline (2-10 micrograms), prostaglandin E2 (10-40 ng), thyrotropin-releasing hormone (0.5-2.0 micrograms) or beta-endorphin (1-3 micrograms) into the preoptic anterior hypothalamus caused a dose-dependent rise in rectal temperature in conscious rats at an ambient temperature of 22 degrees C. In addition, it was found that three intrahypothalamic doses of 10 micrograms of 6-hydroxydopamine at intervals of 2 days caused a significant depletion of noradrenaline in the hypothalamus to 26.4% of control while the concentration of dopamine in the hypothalamus was not significantly reduced at 95.3% of control. Furthermore, the hyperthermic responses induced by prostaglandin E2, thyrotropin-releasing hormone, or beta-endorphin were greatly attenuated after selective depletion of noradrenaline in the hypothalamus in rats. However, selective depletion of noradrenaline did not affect the noradrenaline-induced hyperthermic responses. The data indicate that either prostaglandin E2, thyrotropin-releasing hormone or beta-endorphin may act through the endogenous release of noradrenaline from the hypothalamus to induce hyperthermic responses in rats.