Estradiol coupling to human monocyte nitric oxide release is dependent on intracellular calcium transients: Evidence for an estrogen surface receptor

We tested the hypothesis that estrogen acutely stimulates constitutive NO s ynthase (cNOS) activity in human peripheral monocytes by acting on an estro gen surface receptor. NO release was measured in real time with an amperome tric probe. 17 beta-estradiol exposure to monocytes stimulated NO release w ithin seconds in a concentration-dependent manner, whereas 17 alpha-estradi ol had no effect. 17 beta-estradiol conjugated to BSA (E-2-BSA) also stimul ated NO release, suggesting mediation by a membrane surface receptor. Tamox ifen, an estrogen receptor inhibitor, antagonized the action of both 17 bet a-estradiol and E-2-BSA, whereas ICI 182,780, a selective inhibitor of the nuclear estrogen receptor, had no effect. We further showed, using a dual e mission microfluorometry in a calcium-free medium, that the 17 beta-estradi ol-stimulated release of monocyte NO was dependent on the initial stimulati on of intracellular calcium transients in a tamoxifen-sensitive process. Le eching out the intracellular calcium stores abolished the effect of 17 beta -estradiol on NO release. RT-PCR analysis of RNA obtained from the cells re vealed a strong estrogen receptor-alpha amplification signal and a weak bet a signal. Taken together, a physiological dose of estrogen acutely stimulat es NO release from human monocytes via the activation of an estrogen surfac e receptor that is coupled to increases in intracellular calcium.