Abstract 1887 Pulmonary Vascular Biology Platform, Monday, 5/3

Prostacyclin is a critical mediator of vascular function and growth in the developing lung, where it is produced primarily by the vascular endothelium. A variety of studies in intact animal models indicate that prostacyclin plays a key role in the acute vasodilation of the pulmonary circulation at the time of birth. This is occurring at a time when fetal plasma estrogen levels are rapidly rising due to marked enhancement in placental estrogen synthesis following the onset of parturition. We have previously demonstrated that physiologic levels of estradiol (10-10 to 10-8M) stimulate the production of the vasodilator nitric oxide by ovine fetal pulmonary artery endothelial cells (PAEC). The present studies were designed to determine if estradiol acutely activates prostacyclin production in PAEC. Early passage cells were incubated for 5 to 30 min. in the presence of varying concentrations of 17β-estradiol, and prostacyclin synthesis was determined by radioimmunoassay for 6-keto-prostaglandin F1α, the stable metabolite of prostacyclin. 17β-Estradiol caused a 52% increase in prostacyclin synthesis compared to basal levels (256±30 vs 167±16 pg/well, respectively). The response was evident at 10-10M 17β-estradiol, and it occurred within 5 min of exposure to the hormone. There was no change in prostacylin production in response to 17α-estradiol (10-8 to 10-6M), indicating that the effect is unique to 17β-estradiol. Immunoblot analysis revealed comparable cyclooxygenase type 1 expression and a lack of cyclooxygenase type 2 in control and stimulated cells, signifying that the rapid response is not due to changes in the abundance of the rate-limiting enzyme in prostacyclin synthesis. Thus, the acute mechanism differs significantly from the effects of prolonged 17β-estradiol exposure, which we have previously shown upregulates cyclooxygenase type 1 mRNA and protein expression after 48 h. To determine the potential role of estrogen receptors (ER) in the rapid activation of prostacyclin production, studies were performed in the absence or presence of the ER antagonist ICI 182,780 (10-5M). Concomitant acute treatment with the ICI compound completely prevented 17β-estradiol-induced increases in prostacyclin production. RT-PCR assays and immunoblot analysis revealed expression of the alpha isoform of ER in the PAEC, whereas expression of the beta isoform was not detected. These findings indicate that physiologic concentrations of estradiol cause rapid stimulation of prostacyclin synthesis in fetal PAEC, and that this process is mediated by ER activation. The response most likely involves ERα, but further experiments will be required to exclude the potential role of a previously unknown ER subtype. These mechanisms may underly estrogen-induced vasodilation in both pulmonary and nonpulmonary vascular beds.