EFFECT OF SEX STEROIDS ON BODY-TEMPERATURE IN POSTMENOPAUSAL WOMEN - ROLE OF ENDOGENOUS OPIOIDS

The role of endogenous opioids on the thermoregulatory effect of sex steroids was investigated in six postmenopausal women before and during treatment with transdermal 17 B-estradiol (TTS 50; 50 mcg/day) with or without vaginal progesterone (P4; 1 00 mg twice daily). In all the different endocrine conditions, saline or the opioid antagonist naloxone (10 mg/hr. preceded by 10 mg iv bolus) were randomly infused for 4 hrs., on two consecutive days. Measurements of body temperature (BT) variations were performed by a thermistor probe placed in the rectum. BT did not significantly vary from baseline values during saline infusion, whereas it significantly decreased during the infusion of naloxone performed, either before treatment (p < 0.01), during TTS 50 administration (p < 0.01), or during TTS 50 + P4 (p < 0.025). The naloxone induced decrease of BT was greater during TTS 50 administration than before treatment (p < 0.025). The addition of P4 to TTS 50 administration increased baseline BT of 0.4-degrees-C (p < 0.01), and reduced the ability of naloxone to reduce BT (p < 0.01 vs. TTS 50). The hyperthermic effect of P4 was not abolished by the infusion of naloxone. Our data show that in postmenopausal women the effect of endogenous opioid peptides on BT is enhanced by estradiol and reduced by progesterone. The hyperthermic effect of progesterone does not seem to be mediated by an increased endogenous opioid activity.