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Objectives:The mechanisms regulating basal uteroplacental blood flow (UBF) and the greater than 30-fold increase observed in normal pregnancy remain unclear. Although vascular growth contributes in early gestation, vasodilation accounts for the exponential rise seen in the last third of pregnancy. Large conductance potassium channels (BKCa) are expressed in uterine vascular smooth muscle (VSM), but the extent of their role in regulating UBF in pregnancy is unclear. Therefore, we determined if BKCa regulate basal UBF during ovine pregnancy.Methods:Studies were performed at 113 to 127 days and 135 to 150 days of gestation in eight pregnant ewes instrumented with uterine artery flow probes and uterine arterial and venous catheters. Tetraethylammonium chloride (TEA), a BKCa-specific inhibitor at less than 1.0 mM, was infused intra-arterially into the pregnant uterine horn over 60 minutes to achieve levels of 0.001-0.35 mM while continuously monitoring UBF, arterial pressure (MAP), and heart rate (HR). uterine arterial and venous blood was collected simultaneously to measure uterine cyclic guanosine monophosphate (rGMP) synthesis.Results:Intra-arterial TEA dose-dependently decreased basal UBF in the early (R = 0.81, n = 36, P <.001) an late (R = 0.72, n = 31, P <.001) study periods without altering contralateral UBF, MAP, and HR. The IC50 was 0.2 mM and basal UBF decreased ≥80% at 0.35 mM in both periods. Although UBF fell greater than 40% at estimated plasma TEA levels of 0.3 mM, uterine arterial cGMP was unchanged, uterine venous cGMP rose, and uterine cGMP synthesis was unchanged; therefore, upstream events associated with BKCa activation were unaffected by blockade.Conclusions:These are the first data demonstrating that BKCa are essential in the maintenance of basal UBF in the last third of ovine pregnancy. [ABSTRACT FROM PUBLISHER]

Objective: To determine the mechanism(s) whereby daily and acute estradiol-17β (E2β) exposure modifies endothelium-derived nitric oxide synthase (eNOS) and vascular smooth muscle (VSM) neuronal nitric oxide synthase (nNOS) in reproductive and nonreproductive arteries and to localize NOS isoform expression within the vessel wall. Methods: Oophorectomized nonpregnant ewes received E2β (1 μg/kg per day) or no E2β for 5–6 days or acute E2β (1 μg/kg) on day 6–7 with or without daily E2β. Uterine, mammary, mesenteric, and femoral arteries were collected at completion of each study, adventitia were removed, and samples were frozen and stored at −80C. After separating endothelium and VSM, NOS isoform mRNA was measured using reverse transcription-polymerase chain reaction. VSM nNOS protein was determined by Western analysis. Results: Basal eNOS and nNOS mRNA was greatest (P <.02) in reproductive artery endothelium and VSM, respectively. Daily E2β was required for maximum uterine vascular responses to acute E2β and was associated with increased reproductive artery endothelial eNOS mRNA (> 1.5-fold, P <.02) and uterine VSM nNOS mRNA (> 2.5-fold, P <.003) and protein (21%, P <.05). Acute E2β in the presence and absence of daily E2β also increased uterine eNOS 68% and 28% (P =.01), respectively within 90 minutes but did not affect VSM nNOS. Mammary eNOS increased 71% only after E2β withdrawal; VSM nNOS was unchanged. Neither NOS isoform was altered in nonreproductive arteries by daily or acute E2β. Conclusion: Basal eNOS and nNOS isoform expression is greatest in arteries from reproductive tissues, and isoform responses to E2β are cell specific and transcriptionally regulated. Furthermore, optimal uterine vascular responses to acute E2β exposure require daily E2β exposure that enhances basal NOS expression and abundance. [ABSTRACT FROM AUTHOR]