CHRONIC HORMONE REPLACEMENT THERAPY ALTERS THERMOREGULATORY AND VASOMOTOR FUNCTION IN POSTMENOPAUSAL WOMEN

This investigation examined effects of chronic (greater than or equal to 2 yr) hormone replacement therapy (HRT), both estrogen replacement therapy (ERT) and estrogen plus progesterone therapy (E + P), on core temperature and skin blood flow responses of postmenopausal women. Twe nty-five postmenopausal women [9 not on HRT (NO), 8 on ERT, 8 on E + P ] exercised on a cycle ergometer for 1 h at an ambient temperature of 36 degrees C. Cutaneous vascular conductance (CVC) was monitored by la ser-Doppler flowmetry, and forearm vascular conductance (FVC) was meas ured by using venous occlusion plethysmography. Iontophoresis of brety lium tosylate was performed before exercise to block local vasoconstri ctor (VC) activity at one skin site on the forearm. Rectal temperature (T-re) was similar to 0.5 degrees C lower for the ERT group (P < 0.01 ) compared with E + P and NO groups at rest and throughout exercise. F VC: mean body temperature (T-b) and CVC: Tb curves were shifted simila r to 0.5 degrees C leftward for the ERT group (P < 0.0001). Baseline C VC was significantly higher in the ERT group (P < 0.05), but there was no interaction between bretylium treatment and groups once exercise w as initiated. These results suggest that 1) chronic ERT likely acts ce ntrally to decrease T-re, 2) ERT lowers the T-re at which heat-loss ef fector mechanisms are initiated, primarily by actions on active cutane ous vasodilation, and 3) addition of exogenous progestins in HRT effec tively blocks these effects.