Cytochrome P-450 2C9 pathways contribute to microvascular endothelial function in young males, not females

Endothelium-derived hyperpolarizing factors (EDHF) produced via cytochrome P-450 2C9 (CYP2C9) pathways contribute to vasodilation, but their role in skeletal muscle microvascular reactive hyperemia (RH) remains unclear. Purpose: To determine whether CYP2C9 pathways differentially contribute to forearm microvascular RH in young healthy males and females. Methods: Thirty healthy young adults (22.1±2.2 yrs; 15 females in early follicular phase) completed two randomized, double-blind, counter-balanced experimental visits ≥72 h apart. Participants abstained from caffeine for ≥12h and from vigorous exercise, alcohol, and NSAIDs for ≥24h before visits. Two hours before testing, they randomly ingested 150 mg of fluconazole (FLZ, CYP2C9 inhibitor) or a placebo (PLA). After 15 min of supine rest, baseline muscle oxygenation was recorded for 5 min using near-infrared spectroscopy (NIRS) over the flexor digitorum muscles. While oxygenation data were recorded continuously, RH was elicited by 5-minute cuff occlusion at 230 mmHg, followed by rapid cuff release. Oxy-, deoxy-, and total hemoglobin [Hb] recorded by NIRS to calculate tissue saturation index (TSI% = oxy [Hb] / total [Hb]). Primary study outcomes were: O 2 -deficit AAC (ischemic stimulus), calculated as the area above the desaturation curve during 5 min occlusion below baseline TSI; Reperfusion Rate (RR), the absolute RH index defined as the upslope of TSI recovery over the first 10 s post-occlusion; and Relative RH index (RRH), calculated as RR divided by O 2 -deficit AAC. Results: Means ±SD. There was no main effect of FLZ on O 2 -deficit AAC (p = 0.83), RR (p = 0.27), or RRH (p = 0.32). Regarding sex differences, males exhibited a significantly larger ischemic stimulus (p < 0.001, η 2 p = 0.62) and faster RR (%/s, p < 0.001, η 2 p = 0.36); however, RRH was not significantly different between sexes with a medium effect size (p = 0.2, η 2 p = 0.06). A significant treatment × sex interaction was found for both O 2 -deficit AAC (%.min, males; PLA: 125.9±31.3, FLZ: 136.8±32.4 vs. females; PLA: 77.9±21.1, FLZ: 68.8±14.8, p=0.02, η 2 p=0.18), and RRH (1/min, males; PLA: 0.024±0.005, FLZ: 0.021±0.006 vs. females; PLA: 0.024±0.004, FLZ: 0.026±0.005, p=0.004, η 2 p=0.26). Post-hoc testing showed a reduction in RRH for males (1/min, PLA: 0.024 ± 0.005 vs. FLZ: 0.021 ± 0.006, p = 0.02, d = 0.71) but no effect in females (1/min, PLA: 0.024 ± 0.004 vs. FLZ: 0.026 ± 0.005, p = 0.11, d = 0.44). Conclusion: Males exhibited greater ischemic stimulus and absolute RH response than females. While CYP2C9 inhibition did not change absolute RH indices overall, it revealed a sex-specific effect: FLZ decreased the relative RH index only in males, suggesting a sex-dependent role of the CYP2C9/EDHF pathway in microvascular function. This abstract was presented at the American Physiology Summit 2026 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.