Females respond to baroreceptor stimulation with enhanced modulation of heart rate (HR) to regulate blood pressure and also express greater reliance on nitric oxide (NO) for vascular control compared to males. Sex differences in muscle oxygenation consequent to central hemodynamic challenge induced by systemic NO synthase (NOS) inhibition are unknown. We tested the hypotheses that systemic NOS inhibition would induce lower contracting skeletal muscle oxygenation in females compared to males. The spinotrapezius of Sprague-Dawley rats (females (♀) = 9, males (♂) = 9) was surgically exposed and contracted by electrical stimulation (180s, 1 Hz, ~6 V) under pentobarbital sodium anesthesia. Oxyphor G4 was injected into the muscle and phosphorescence quenching was used to measure the interstitial PO2 (PO2is, determined by O2 delivery-to-utilization matching) under control (Krebs-Henseleit solution) and after intra-arterial infusion of nitro-l-arginine methyl ester (l-NAME; NOS blockade; 10 mg kg-1). At rest, females showed a greater PO2is increase (ΔPO2is/ΔMAP) and HR (ΔHR/ΔMAP) reduction than males in response to the elevated MAP induced by systemic NOS inhibition (both p < 0.05). Following l-NAME, during the contracting steady-state, females exhibited lower PO2is than males (♂: 17.1 ± 1.4 vs ♀: 10.8 ± 1.4 mmHg, p < 0.05). The rate pressure product was lower in females than males (♂: 482 ± 14 vs ♀: 392 ± 29, p < 0.05) and correlated with the steady-state PO2is (r = 0.66, p < 0.05). These results support that females express greater reductions in HR than males in response to l-NAME-induced elevation of MAP via the baroreceptor reflex and provide new insights on how central hemodynamics affect skeletal muscle oxygenation in a sex-specific manner.

中文翻译：

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全身性NOS抑制作用在完整雌性大鼠中比在雄性大鼠中更能减少收缩肌肉的氧合作用。

与男性相比，女性对压力感受器刺激的反应增强了心率（HR）的调节以调节血压，并且还表达了对一氧化氮（NO）的血管控制依赖性。由全身性NO合酶（NOS）抑制引起的中央血流动力学挑战导致的肌肉氧合作用的性别差异未知。我们测试了以下假设，即与男性相比，全身性NOS抑制可导致女性骨骼肌收缩程度更低。在戊巴比妥钠麻醉下，通过电刺激（180s，1 Hz，〜6 V）对Sprague-Dawley大鼠（女性（♀）= 9，男性（♂）= 9）的斜方肌进行手术暴露和收缩。将Oxyphor G4注入肌肉，并使用磷光淬灭法测量间质PO2（PO2is，通过在控制下（Krebs-Henseleit溶液）和动脉内灌注硝基-1-精氨酸甲酯（I-NAME; NOS阻滞; 10 mg kg-1）测定氧含量。静息时，响应全身性NOS抑制引起的MAP升高，女性的PO2is升高（ΔPO2is/ΔMAP）和HR（ΔHR/ΔMAP）降低均高于男性（均p <0.05）。遵循l-NAME，在收缩稳态期间，女性表现出的PO2is低于男性（♂：17.1±1.4 vs♀：10.8±1.4 mmHg，p <0.05）。女性的速率压力乘积低于男性（♂：482±14 vs♀：392±29，p <0.05），并且与稳态PO2is相关（r = 0.66，p <0.05）。