Estrogen selectively up-regulates eNOS and nNOS in reproductive arteries by transcriptional mechanisms.

Objective: To determine the mechanism(s) whereby daily and acute estradiol-17beta (E(2)beta) 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 E(2)beta (1 microg/kg per day) or no E(2)beta for 5-6 days or acute E(2)beta (1 microg/kg) on day 6-7 with or without daily E(2)beta. 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 E(2)beta was required for maximum uterine vascular responses to acute E(2)beta 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 E(2)beta in the presence and absence of daily E(2)beta 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 E(2)beta withdrawal; VSM nNOS was unchanged. Neither NOS isoform was altered in nonreproductive arteries by daily or acute E(2)beta.

Conclusions: Basal eNOS and nNOS isoform expression is greatest in arteries from reproductive tissues, and isoform responses to E(2)beta are cell specific and transcriptionally regulated. Furthermore, optimal uterine vascular responses to acute E(2)beta exposure require daily E(2)beta exposure that enhances basal NOS expression and abundance.