Nélida Polini

Progesterone and 17 β-estradiol acutely stimulate nitric oxide synthase activity in rat aorta and inhibit platelet aggregation

The rapid non-genomic stimulatory action of progesterone (Pg) and estradiol (E2) on nitric oxide synthase (NOS) activity of endothelium intact aortic rings and its effect on platelet aggregation was investigated. First we measured the effect of the hormones on platelet aggregation when added to rat aortic strips (RAS) incubated in a PRP. RAS induced an antiaggregatory activity, which was enhanced by the presence of the hormones. The inhibitory action induced by the hormones was evoked in a dose dependent manner (10 pM-100 nM). These effects are specific for progesterone and 17-beta-estradiol, since either testosterone and 17-alpha-estradiol were devoid of activity. The hormones induced rapid responses, producing significant inhibition within 1 to 5 minutes of hormonal exposure. The addition of 10(-5) M L-NAME suppressed the antiaggregatory effect of 1 nM E2 or 10 nM Pg. Furthermore, we specifically quantified the NO generation by the 3H-citrulline technique. 10(-8) M E2 induced 2-fold increase of RAS citrulline production, while the increment induced by 10(-7) M Pg was 55% over control. Preincubation with 10(-5) M L-NAME completely suppressed the stimulatory action of 10(-9) M E2 or 10(-8) M Pg, confirming that the antiaggregatory factor released from the aortic tissue was NO. Preincubation with cycloheximide did not block the increment in NO induced by the hormones. In conclusion the present study provides for the first time evidence of acute, non-genomic effects of Pg on rat aorta NOS activity and platelet aggregation in coincidence with the results obtained with estradiol treatment.

Novel action of estrone on vascular tissue : regulation of NOS and COX activity

The hypothesis tested in the present work is that estrone non-genomically regulates aortic nitric oxide synthase (NOS) and cyclooxygenase (COX) activities in female rats, and that such regulation depends on ovarian function. We found that physiological concentrations of estrone (E(1)) (0.1-10nM) significantly increased nitric oxide (NO) production (133 and 163% above control). The stimulatory action of E(1) on NOS activity was independent of calcium influx since the increase in NO elicited by the hormone was not affected by EGTA or verapamil. When COX activity was measured, we observed that estrone enhanced thromboxane (TXB(2)) production and prostacyclin (PGI(2)) release, but not prostaglandin (PGF(2), PGD(2), and PGE(2)) synthesis. Finally we demonstrated that the hormonal effect on NOS activity was not detected in rat aortic strips (RAS) isolated from animals deprived of ovarian activity (FR(-)) or ovariectomized rats (OVX). These results suggest that estrone exerts a direct, non-genomic action on rat aortic metabolism, which involves NOS and COX activation and depends on ovarian activity.

Effect of genistein and raloxifene on vascular dependent platelet aggregation.

We checked the hypothesis whether the non-classical estrogen receptor modulators genistein and raloxifene could affect platelet aggregation through their direct effect on vascular tissue by regulating the synthesis of vasoactive compounds. In rat aortic strips, 10nM genistein or 10nM raloxifene significantly increased nitric oxide synthesis, event prevented by ICI182780. Both agents exhibited an antiaggregatory action, dependent on the nitric oxide release from vascular tissue, since preincubation of aortic strips with L-NAME partially and completely suppressed the inhibition of platelet aggregation induced by genistein or raloxifene respectively. The phytoestrogen enhanced phospholipase A(2) and prostacyclin release into the incubation medium. Indomethacin reduced in half the inhibition of platelet aggregation elicited by genistein. Finally, genistein or raloxifene also inhibited platelet aggregation in aortic strips from ovariectomized rats. In conclusion, genistein and raloxifene exhibit an antiplatelet activity through their direct action on vascular tissue, in rats with or without ovarian activity.