Influence of female reproductive hormones on local thermal control of skinblood flow

Progesterone and estrogen modify thermoregulatory control such that, when b oth steroids are elevated, body temperature increases and the reflex thermo regulatory control of cutaneous vasodilation is shifted to higher internal temperatures. We hypothesized that the influence of these hormones would al so include effects on local thermal control of skin blood flow. Experiments were conducted in women in high-hormone (HH) and low-hormone (LH) phases o f oral contraceptive use. Skin blood flow was measured by laser-Doppler flo wmetry, and local temperature (T-loc) was controlled over 12 cm(2) around t he sites of blood flow measurement. Ti,, was held at 32 degrees C for 10-15 min and was then decreased at one site from 32 to 20 degrees C in a ramp o ver 20 min. Next, T-loc was increased from 32 to 42 degrees C in a ramp ove r 15 min at a separate site. Finally, T-loc at both sites was held at 42 de grees C for 30 min to elicit maximum vasodilation; data for cutaneous vascu lar conductance (CVC) are expressed relative to that maximum. Whole body sk in temperature (T-sk) was held at 34 degrees C throughout each study to min imize reflex effects from differences in T-sk between experiments. Baseline CVC did not differ between phases [8.18 +/- 1.38 (LH) vs. 8.41 +/- 1.31% o f maximum (HH); P > 0.05]. The vasodilator response to local warming was au gmented in HH (P < 0.05, ANOVA). For example, at T-loc of 40-42 degrees C, CVC averaged 76.41 +/- 3.08% of maximum in HH and 67.71 +/- 4.43% of maximu m in LH (P < 0.01 LH vs. HH). The vasoconstrictor response to local cooling was unaffected by phase (P > 0.05). These findings indicate that modificat ions in cutaneous vascular control by female steroid hormones include enhan cement of the vasodilator response to local warming and are consistent with reports of the influence of estrogen to enhance nitric oxide-dependent vas odilator responses.