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 adrenergic cutaneous vasoconstrictor system, we conducted ramp decreases in skin temperature (T-sk) in eight women in both high- and low (placebo)-progesterone/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 vasoconstrictor activity) and was then decreased in a ramp, similar to 0.2 degrees C/min for 12-15 min. Subjects rested supine for 30-40 min before each experiment, and the protocol was terminated before the onset of shivering. Skin blood flow was monitored by laser-Doppler flowmetry and arterial pressure by finger photoplethysmography. In all experiments, cutaneous vasoconstriction began immediately with the onset of cooling, and cutaneous vascular conductance (CVC) decreased progressively with decreasing Tsk Regression analysis of the relationship of CVC to T-sk showed no difference in slope between 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 blockade confirmed this response as being solely due to the adrenergic vasoconstrictor 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 degrees C, respectively; P < 0.02). Integrative analysis of CVC in terms of simultaneous values for T-sk and T-or showed that the cutaneous vasoconstrictor response was shifted in the high-hormone phase such that a higher T-or was maintained throughout cooling (P < 0.05). Thus reflex thermoregulatory control of the cutaneous vasoconstrictor system is shifted to higher internal temperatures by exogenous female reproductive hormones.