Sex steroid regulation of beta-adrenergic sensitive adenylate cyclase in rabbit myometrial cells in primary culture.

Cyclic adenosine 3'-5'-monophosphate (cAMP) is the likely mediator of myometrial relaxation induced by agents like isoproterenol and relaxin. In vivo, the relaxation response to beta-adrenergic catecholamines is modulated by estradiol (E2) and progesterone (P) during the estrous cycle and pregnancy. However, it is still debated whether that regulation occurs via a direct action on myometrial cells or indirectly through modulation of adrenergic neurotransmitters. We have studied the properties of adenylate cyclase in primary cultures of smooth muscle cells isolated from rabbit myometrium. Adenylate cyclase activity increased with time in culture reaching a maximum on day 6. The cultured cells had basal activity which could be stimulated by guanosine triphosphate (GTP, 2.3 fold), its non-hydrolysable analogue guanylyl-imido-diphosphate (GPP[NH]p, 8.3 fold) and sodium fluoride (NaF, 15.7 fold). Isoproterenol (Iso) and prostaglandin E2 (PGE2) stimulated adenylate cyclase activity to the same level (4 fold) and required the presence of exogenous GTP. Sex steroid treatment did not affect basal activity or its stimulation by guanyl nucleotides, PGE2 or NaF. However, the adenylate cyclase response to Iso was significantly affected by E2 and/or P treatment. E2 treatment for 6 days diminished the sensitivity 10 fold (from 10 nM to 100 nM) while E2 for 3 days followed by P for 3 days increased it 10 fold (to 1 nM). Maximal response was not affected by treatment with E2 for 6 days but was diminished by 43% (p less than 0.001) when P was added alone and increased by 63% (p less than 0.001) when P was added following E2 pretreatment. Our results demonstrate that sex steroids can alter beta-adrenergic response in vitro by a direct action on myometrial cells.