Hypertension, a leading risk factor for death, impacts 40% of American women but is far more frequent after menopause. Postmenopausal hypertension is largely related to the pronounced decline in circulating estrogen associated with menopause, but the molecular mechanisms involved remain incompletely defined. In addition to activating the classical estrogen receptors (ER and ERβ), estrogen activates the G protein-coupled estrogen receptor 1 (GPER1), which elicits cardiovascular protective actions. Our preliminary data uncovered that (1) aged female global GPER1-knockout (GPER1 KO) mice have higher blood pressure than wild-type littermates do, and (2) GPER1 regulates renal endothelin-1 signaling and the activity of epithelial Na+ channel (ENaC), a major regulator of natriuresis and, thereby, blood pressure. To further investigate the GPER1-ENaC interaction, we generated mice with GPER1 deletion specifically in renal collecting duct principal cells (PC-GPER1 KO mice). Patch clamp electrophysiology experiments revealed greater ENaC activity in collecting ducts isolated from PC- GPER1 KO female mice. Conversely, pharmacologic activation of GPER1 downregulated ENaC activity in collecting ducts obtained from wild-type female mice. In aged GPER1 KO mice, prior pregnancy resulted in lower blood pressure, increased plasma E2 level and decreased adrenal production of aldosterone, which also regulates ENaC and blood pressure. In line with this finding, estrogen-mediated activation of adrenal ERβ has been shown to blunt aldosterone biosynthesis when GPER1 is silenced. Of note, most animal research with females utilizes virgin animals, which does not represent the overall female population, and the impact of uncomplicated pregnancy on later maternal blood pressure is unclear. Our preliminary data suggest GPER1 signaling may contribute to the later-in-life cardiovascular benefits of pregnancy previously observed in longitudinal studies of women. We hypothesize that GPER1 signaling and prior pregnancies elicit blood pressure -lowering actions in aged females by downregulating ENaC via regulation of ET-1 and aldosterone, respectively. AIM 1 of our study will determine whether GPER1 activation lowers blood pressure by downregulating collecting duct ENaC in aged female mice. AIM 2 will determine whether prior pregnancy lowers blood pressure in global GPER1 KO mice by improving ovarian function and downregulating aldosterone signaling. Simultaneously, using existing human genotyping, reproductive history and prospectively collected blood pressure data in BioVU, Vanderbilt University Medical Center's vast DNA repository, AIM 3 will examine the associations of candidate genetic variants of GPER1 and parity with blood pressure in postmenopausal nulliparous and parous women. Successful completion of the current studies will likely justify the development of antihypertensive therapeutics that target GPER1 for postmenopausal hypertension. Furthermore, the proposed studie...