Does Biological Sex Modulate the Neural Control of Body Temperature during Heat Stress?

Introduction: Understanding how thermoregulatory responses differ between males and females could contribute to a better understanding of sex-related differences in heat vulnerability. Previous studies have established that maximal sweating capacity is greater in males, likely due to greater cholinergic sensitivity of the eccrine sweat glands. However, it remains unknown if the neural control of body temperature during heat stress differs between males and females. OBJECTIVE & HYPOTHESIS: The objective of this study is to determine the effect of biological sex on the neural control of body temperature during heat stress. We hypothesized that the onset threshold for increases in skin sympathetic nerve activity (SSNA), local sweat rate (LSR), and cutaneous vascular conductance (CVC) would not differ between males and females during passive heat stress. Methods: Nine healthy males (23 to 32 years old) and eight healthy females (21 to 36 years old, low reproductive hormone phase) were exposed to passive heat stress with a water-perfused suit until core temperature increased by 1.2°C. SSNA was measured from the radial nerve by microneurography, on the same arm as measurements of forearm LSR and CVC. Core temperature was measured with an esophageal probe and mean skin temperature was calculated as a weighted mean of four measurement sites. Mean body temperature was calculated as a weighted summation of core (0.8) and mean skin (0.2) temperatures to determine the onset threshold for SSNA, LSR and CVC by segmented linear regression. Data are presented as mean ± standard deviation or mean differences (males – females) with [95% confidence interval]. Results: Baseline mean body temperature was 36.08 ± 0.23°C for males and 36.29 ± 0.23°C for females. The change in mean body temperature at the onset threshold for SSNA was 0.59 ± 0.14°C for males and 0.89 ± 0.12°C for females (mean difference: -0.30°C [-0.43, -0.17]). The change in mean body temperature at the onset threshold for forearm LSR was 0.80 ± 0.25°C for males and 0.92 ± 0.26°C for females (mean difference: -0.12°C [-0.37, 0.13]). The change in mean body temperature at the onset threshold for forearm CVC was 0.80 ± 0.27°C for males and 0.89 ± 0.26°C for females (mean difference: -0.09°C [-0.36, 0.19]). Conclusion: These preliminary results suggest that females require a greater change in mean body temperature to increase skin sympathetic nerve activity, local sweat rate, and cutaneous vascular conductance during passive heat stress. The physiological importance of the differences observed remains to be determined. Natural Sciences and Engineering Research Council of Canada This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.