Influence of female reproductive hormones on local thermal control of skin blood flow

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Abstract
Progesterone and estrogen modify thermoregulatory control such that, when both steroids are elevated, body temperature increases and the reflex thermoregulatory control of cutaneous vasodilation is shifted to higher internal temperatures. We hypothesized that the influence of these hormones would also include effects on local thermal control of skin blood flow. Experiments were conducted in women in high-hormone (HH) and low-hormone (LH) phases of oral contraceptive use. Skin blood flow was measured by laser-Doppler flowmetry, and local temperature (Tloc) was controlled over 12 cm2 around the sites of blood flow measurement. Tloc was held at 32°C for 10–15 min and was then decreased at one site from 32 to 20°C in a ramp over 20 min. Next, Tloc was increased from 32 to 42°C in a ramp over 15 min at a separate site. Finally, Tloc at both sites was held at 42°C for 30 min to elicit maximum vasodilation; data for cutaneous vascular conductance (CVC) are expressed relative to that maximum. Whole body skin temperature (Tsk) was held at 34°C throughout each study to minimize reflex effects from differences in Tsk between experiments. Baseline CVC did not differ between phases [8.18 ± 1.38 (LH) vs. 8.41 ± 1.31% of maximum (HH); P > 0.05]. The vasodilator response to local warming was augmented in HH (P < 0.05, ANOVA). For example, at Tloc of 40–42°C, CVC averaged 76.41 ± 3.08% of maximum in HH and 67.71 ± 4.43% of maximum 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 modifications in cutaneous vascular control by female steroid hormones include enhancement of the vasodilator response to local warming and are consistent with reports of the influence of estrogen to enhance nitric oxide-dependent vasodilator responses.