Reflex control of cutaneous vasoconstrictor system is reset by exogenous female reproductive hormones

To determine whether cardiovascular influences of exogenous female steroid hormones include effects on reflex thermoregulatory control of the adrenerg ic cutaneous vasoconstrictor system, we conducted ramp decreases in skin te mperature (T-sk) in eight women in both high- and low (placebo)-progesteron e/estrogen phases of oral contraceptive use. With the use of water-perfused suits, T-sk was held at 36 degrees C for 10 min (to minimize initial vasoc onstrictor activity) and was then decreased in a ramp, similar to 0.2 degre es C/min for 12-15 min. Subjects rested supine for 30-40 min before each ex periment, and the protocol was terminated before the onset of shivering. Sk in blood flow was monitored by laser-Doppler flowmetry and arterial pressur e by finger photoplethysmography. In all experiments, cutaneous vasoconstri ction began immediately with the onset of cooling, and cutaneous vascular c onductance (CVC) decreased progressively with decreasing Tsk Regression ana lysis of the relationship of CVC to T-sk showed no difference in slope betw een phases (low-hormone phase: 17.67 +/- 5.57; high-hormone phase: 17.40 +/ - 8.00 %baseline/degrees C; P > 0.06). Additional studies involving local b lockade confirmed this response as being solely due to the adrenergic vasoc onstrictor system. Waking oral temperature (T-or) was significantly higher on high-hormone vs, low-hormone days (36.60 +/- 0.11 vs. 36.37 +/- 0.09 deg rees C, respectively; P < 0.02). Integrative analysis of CVC in terms of si multaneous values for T-sk and T-or showed that the cutaneous vasoconstrict or response was shifted in the high-hormone phase such that a higher T-or w as maintained throughout cooling (P < 0.05). Thus reflex thermoregulatory c ontrol of the cutaneous vasoconstrictor system is shifted to higher interna l temperatures by exogenous female reproductive hormones.