OVARIAN HORMONES REGULATE ALPHA(1)-ADRENOCEPTOR AND BETA-ADRENOCEPTORINTERACTIONS IN FEMALE RAT PINEALOCYTES

WE have examined the effects of alpha(1)- and beta-receptor activation on cyclic AMP (cAMP) accumulation in cultured pinealocytes from femal e ovariectomized rats, and from intact rats at proestrus treated with the antiestrogen Tamoxifen, the antiprogestagen RU486, or with both. I soproterenol (a beta-agonist) significantly increased cAMP levels in p inealocytes from intact and ovariectomized rats. This response was con siderably enhanced in pinealocytes from rats treated with RU486 or Tam oxifen alone, but not with both. Moreover, incubation of pinealocytes with isoproterenol together with phenylephrine (an alpha(1)-agonist) p roduced a synergistic effect in animals that had been ovariectomized, or that had received RU486, either alone or in combination with Tamoxi fen. These results suggest that, in female rats, ovarian steroids may regulate the interactions between alpha 1- and beta-adrenergic recepto rs, and thus modulate pineal melatonin synthesis during the oestrous c ycle through these mechanisms.