Popliteal flow-mediated dilatory responses to an acute bout of prolonged sitting between earlier and later phases of natural menstrual and oral contraceptive pill cycles.

Uninterrupted sitting can impair popliteal flow-mediated dilation (FMD) responses in young, premenopausal females when endogenous or exogenous estrogen levels are low. However, it is unknown whether sitting-induced FMD responses are altered when estrogen levels are elevated in females who naturally menstruate (NAT) or those using combined, monophasic oral contraceptive pills (OCP). This study tested the hypothesis that the decline in popliteal FMD following an acute bout of prolonged sitting would be attenuated during the later versus earlier phases of a natural menstrual or OCP cycle. Popliteal FMD was measured before and after 3 h of sitting in NAT females (n = 9; 23 ± 3 yr) and OCP females (n = 9; 23 ± 3 yr) during both of their respective phases. At pre-sit, relative FMD was greater in the later phase versus earlier phase in NAT (4.6 ± 1.6% to 5.8 ± 1.5%; P = 0.002) but not between pill phases among OCP (4.4 ± 1.2% to 4.8 ± 1.6%; P = 0.32). Both groups exhibited similar prolonged sitting-induced impairments in popliteal FMD (pre- to post-sitting time: P < 0.001; group ΔFMD: P = 0.66; phase ΔFMD: P = 0.42; interaction ΔFMD: P = 0.72) regardless of menstrual cycle phase (earlier: -2.5 ± 1.5%; later: -2.4 ± 1.0%) or pill phase (inactive pill: -2.4 ± 1.4%; active pill: -2.1 ± 1.1%). Our findings demonstrate that lower-limb arterial endothelial-dependent vasodilatory function was enhanced in the later versus earlier menstrual phase among NAT but unaffected by combined, monophasic pill phases in OCP. Furthermore, healthy, young females exhibited pronounced negative lower-limb vascular effects in response to prolonged sitting regardless of whether they were in the earlier or later phases of a natural menstrual or contraceptive pill cycle.NEW & NOTEWORTHY We compared changes in popliteal artery endothelial function to a 3-h bout of sitting in females across their natural menstrual or oral contraceptive pill cycles. Pre-sitting endothelial-dependent vasodilation was greater in females who naturally menstruate during the later versus earlier phase but unchanged among contraceptive pill phases. Neither menstrual nor oral contraceptive pill phases attenuated the robust decline in conduit artery health following an acute period of uninterrupted sitting in young females.