Effect of luteal phase elevation in core temperature on forearm blood flow during exercise

Forearm blood flow (FBF) as an index of skin blood flow in the forearm was measured in five healthy women by venous occlusion plethysmography during leg exercise at 80% peak aerobic power and ambient temperature of 35 degrees C (relative humidity 22%; dew-point temperature 10 degrees C). Resting esophageal temperature (T(es)) was 0.3 +/- 0.1 degrees C higher in the midluteal than in the early follicular phase of the menstrual cycle (P < 0.05). Resting FBF was not different between menstrual cycle phases. The T(es) threshold for onset of skin vasodilation was higher (37.4 +/- 0.2 degrees C) in midluteal than in early follicular phase (37.0 +/- 0.1 degrees C; P < 0.05). The slope of the FBF to T(es) relationship was not different between menstrual cycle phases (14.0 +/- 4.2 ml x 100 ml(-1) x min(-1) x degrees C(-1) for early follicular and 16.3 +/- 3.2 ml x 100 ml(-1) x min(-1) x degrees C(-1) for midluteal phase). Plateau FBF was higher during exercise in midluteal (14.6 +/- 2.2 ml x 100 ml(-1) x min(-1) x degrees C(-1)) compared with early follicular phase (10.9 +/- 2.4 ml x 100 ml(-1) x min(-1) x degrees C(-1); P < 0.05). The attenuation of the increase in FBF to T(es) occurred when T(es) was 0.6 degrees C higher and at higher FBF in midluteal than in early follicular experiments (P < 0.05). In summary, the FBF response is different during exercise in the two menstrual cycle phases studied. After the attenuation of the increase in FBF and while T(es) was still increasing, the greater FBF in the midluteal phase may have been due to the effects of increased endogenous reproductive endocrines on the cutaneous vasculature.