Influence of menstrual cycle phase on inflammatory and vascular responses to acute passive heating in healthy young women

The aim of this study was to determine whether inflammatory and vascular responses to passive heating differ between the early follicular phase (EFP) and the mid-luteal phase (MLP) of the menstrual cycle. Ten healthy, naturally menstruating females (26 ± 3 years of age; body mass index 21.4 ± 1.9 kg/m²) were assessed during EFP and MLP. Participants underwent 60 min whole-body passive heat exposure (71°C ± 2°C, dry heat) in both phases. Outcomes included body temperature, interleukin-6, interleukin-1 receptor antagonist and plasma nitrite concentrations, cutaneous vascular conductance, blood pressure, arterial stiffness and perceptual responses. Rectal temperature and mean skin temperature increased during heat exposure but did not differ between EFP and MLP. Likewise, heat exposure increased interleukin-6, interleukin-1 receptor antagonist and plasma nitrite concentrations, with no differences between menstrual cycle phases. However, brachial (EFP, 75 ± 4 mmHg vs MLP, 72 ± 5 mmHg; p = 0.040) and central (EFP, 75 ± 4 mmHg vs MLP, 72 ± 5 mmHg; p = 0.042) mean arterial pressures were higher in EFP than in MLP at 40 min of heat exposure. Additionally, arterial stiffness declined more in EFP (-13% ± 7%) than in MLP (-5% ± 6%; p = 0.019) from the end of heat exposure to 30 min into recovery. Perceptual responses, including thermal sensation and comfort, were similar between menstrual cycle phases, but skin wetness perception was heightened during EFP. In conclusion, the inflammatory and plasma nitrite responses to passive heating did not differ between EFP and MLP. However, some vascular function and perception parameters were affected by the menstrual cycle phase.