Differential Effects of Warm- and Cold-Ambient Temperature on Blood Levels of β-Endorphin and Prolactin in the Rat

Abstract

A comparison of the effects of warm- and cold-ambient temperature and physical immobilization on blood levels of immunoreactive β-endorphin (β-END) and prolactin (PRL) in rats was made. Both physical restraint (15–45 min) and warm-ambient temperature (36°, 20 to 360 min) evoked increases in circulating levels of β-END and PRL. By contrast, exposure to cold-ambient temperature (4°, 7 1/2 to 360 min) increased blood levels of β-END but decreased circulating PRL. This divergence in plasma levels of β-END and PRL in cold-exposed animals suggests that: (i) separate hypothalamic mechanisms regulate the secretion of these two hormones, and (ii) bloodborne β-END does not normally stimulate PRL in cold-exposed rats. Therefore, under the present conditions the secretion of pituitary prolactin appears to be directly related to changes in body temperature and not plasma levels of immunoreactive β-END.