Effect of Sex on Sympatho-inhibitors and Non-inhibitor Phenotypes during Acute Hyperoxia

Acute hyperoxia (i.e., breathing air consisting of 100% oxygen, O2) reduces muscle sympathetic nerve activity (MSNA), positioning hyperoxia as a potential anti-hypertensive therapeutic. However, the link between hyperoxia and MSNA has not been established in females. We tested the hypothesis that males would exhibit greater reductions in MSNA during hyperoxia than females. We tested healthy females (n=18, 27±5yr, body mass index [BMI] 23±3kg/m2) and males (n=13, 27±5yr, 25±3kg/m2) of similar age (P=0.99) and BMI (P=0.08). Integrated MSNA, blood pressure, and end-tidal O2 (ETO2) and CO2 (ETCO2) were measured during normal room air breathing (BSL; 3-min) and hyperoxic breathing (100% O2; 3-min). Integrated MSNA was quantified as burst frequency (BF; bursts/min), amplitude (BA; a.u.), and total MSNA (a.u.); blood pressure was quantified as mean arterial pressure (MAP). Baseline MSNA BF was not different between females and males (24±7 vs 23±8 bursts/min, respectively, P=0.68); MAP was lower in females than males (85±7 vs 93±7 mmHg; p<0.01). Hyperoxia increased ETO2 (effect of cond: p<0.01) and reduced ETCO2 (effect of cond: p<0.01) in a manner similar between sexes for ETO2 (sex*cond: P=0.56) whereas ETCO2 decreased more in females than males (sex*cond: P=0.01). Overall, hyperoxia evoked reductions in MSNA BF (effect of cond: P=0.02) but not BA (effect of cond: P=0.80) or total MSNA (effect of cond: P=0.26). Nadir MSNA responses during hyperoxia unveiled sex differences insofar as total MSNA was reduced consistently only in males (sex*cond: P=0.04); within the females we observed the presence of sympatho-inhibitors and non-inhibitors. Whereas female and male inhibitors reduced total MSNA via substantial reductions in BF and non-significant reductions in BA, female non-inhibitors demonstrated limited reductions in BF (P=0.11 vs inhibitors) coupled with increases in BA (p<0.01 vs inhibitors), resulting in no net change in total MSNA (p<0.01 vs inhibitors). Overall, these findings indicate sex differences exist in the sympathetic response to hyperoxia, in marked variability in the female sympathetic response to acute hyperoxia. The Women and Children's Health Research Institute. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.