Endocrine influences on the actions of morphine. III. Responses to hypothalamic hormones

As part of an assessment of endocrine influences on the actions of morphine, we have studied the effects of intracerebroventricular administration of somatostatin and thyrotropin releasing hormone (TRH) on the antinociceptive, temperature and cataleptic responses to subcutaneous morphine in both intact and hypophysectomized rats. Somatostatin significantly antagonized morphine-induced antinociception in intact, but not in hypophysectomized, animals. TRH, on the other hand, had no effect on antinociceptive response to morphine in either intact or hypophysectomized animals. Neither hormone altered hyperthermic response to morphine but TRH antagonized the hypothermic response. Similarly, TRH antagonized the cataleptic actions of morphine whereas somatostatin had no effect. These results indicate that somatostatin and TRH can attenuate certain actions of morphine in vivo and suggest that specific opiate actions may be modulated by specific hypothalamic hormones.