Estrogen acutely stimulates endothelial nitric oxide synthase in H441 human airway epithelial cells

Nitric oxide (NO) is an important mediator of physiologic processes in the airway. Levels of exhaled NO are greatest and asthma symptoms are least in menstruating women during midcycle, when estrogen levels are highest. To be tter understand the role of estrogen in airway function, we tested the hypo thesis that estrogen stimulates endothelial NO synthase (eNOS) in NCI-H441 human bronchiolar epithelial cells, eNOS activation was assessed by measuri ng conversion of [H-3]L-arginine to [H-3]L-citrulline in intact cells. eNOS activity rose in the presence of estradiol-17 beta (E(2)beta), with a maxi mum stimulation of 243% at 10(-8) M E(2)beta. This response was comparable to the 201% increase elicited by the calcium (Ca2+) ionophore A23187 (10(-5 ) M), and was evident as early as 5 min after such treatment. Actinomycin D had no effect on the response to E(2)beta, and eNOS abundance was similar in control and E(2)beta-treated cells. E(2)beta-stimulated eNOS activity wa s dependent on the influx of extracellular Ca2+, and was completely inhibit ed by the estrogen receptor (ER) antagonist ICI182,780. Messenger RNA and p rotein for the or isoform of ER (ER alpha) were evident in the H441 cells, and freshly isolated ovine airway epithelial cells also coexpressed eNOS an d ER alpha. These findings indicate that estrogen acutely activates existin g eNOS in H441 airway epithelial cells, through a process that involves the stimulation of epithelial ER and Ca2+ influx. This process may play a role in the hormonal modulation of airway function.