Sex Differences in the Contribution of Sensory Nerves to Rapid Cutaneous Vasodilation During Local Heating in Young Humans
Authors: Martin Zachary T. , Soave Kayla M. , Del Pozzi Andrew T. 
Published: June 2021

Cutaneous blood flow rapidly increases in skin sites encountering local thermal stimuli. Sensory nerves primarily modulate this response. Age‐, fitness‐, and regional‐related differences in sensory nerve‐mediated rapid cutaneous thermal hyperemia have been discovered; however, it remains unknown if there are sex differences in this response. We sought to determine if there were sex differences in the contribution of sensory nerves to rapid cutaneous thermal hyperemia.METHODSFifteen healthy human females (age 23 ± 4 years, tested once during the early follicular (EF) phase and once during the mid‐luteal (ML) phase of their menstrual cycle) and 15 healthy human males (age 23 ± 2 years) had a 4 cm2 area on one forearm and one leg treated with a eutectic mixture of local anesthetic (EMLA cream; sensory nerve blocker). After confirming sensory nerve blockade by brushing a hypodermic needle over the treated sites, EMLA and control sites were instrumented with laser‐Doppler flowmetry probes and local skin heaters. Blood pressure was measured every 5 min on the contralateral arm. Baseline (33 °C) skin blood flow data were measured for 10 min before increasing the local skin temperature at each site by 1 °C • 20 s−1 to 42 °C to induce rapid cutaneous vasodilation. Once skin blood flow plateaued after 30 min at 42 °C, the local skin temperature was raised to 44 °C for 30 min to achieve maximal vasodilation. Data were expressed as a percentage of maximal cutaneous vascular conductance (%CVCmax).RESULTSThe contribution of sensory nerves to rapid cutaneous thermal hyperemia in the forearm of females in the ML phase was 41 ± 17%CVCmax compared to 24 ± 18%CVCmax in males (p = .02), while females in the EF phase exhibited a sensory nerve contribution of 33 ± 19%CVCmax compared to the 24 ± 18%CVCmax in males (p = .20). In the leg, the contribution of sensory nerves was 32 ± 19%CVCmax for females in the ML phase and 16 ± 15%CVCmax in males (p = .02), while females in the EF phase experienced a contribution of sensory nerves of 28 ± 21%CVCmax compared to 16 ± 15%CVCmax males (p = .10).CONCLUSIONHuman females who were in the ML phase of the menstrual cycle (high levels of estrogen and progesterone) exhibited a greater contribution of sensory nerves to rapid cutaneous vasodilation in the forearm and leg when the skin was locally heated compared to males. Since estrogen administration has been shown to augment rapid cutaneous thermal hyperemia, the sex differences discovered in this study (during the ML phase only) could be attributed to elevated female sex hormones during the ML phase, especially estrogen. These findings expand on the age‐, regional‐, and fitness‐related differences previously identified in sensory nerve‐mediated rapid cutaneous thermal hyperemia and further other recent work showing sex differences in cutaneous vascular control mechanisms. Future research in this area should control for sex differences when studying rapid cutaneous thermal hyperemia and determine whether males exhibit increased reliance on a separate vasodilatory mechanism by which they are able to achieve the same level of rapid cutaneous vasodilation during local heating.Support or Funding InformationThis study was supported in part by an Aspire Student Research Program grant through Ball State University.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.