Effect of estrogen on intracellular signaling pathways linked to activation of M2- and M3-muscarinic acetylcholine receptors in the rat myometrium

The estrogen treatment of adult female rats induces an increase in myometrium sensitivity to cholinergic agonists and in this tissue the presence of M-2- and M-3-muscarinic acetylcholine (mACh) receptor was shown. We now report the effect of estrogen on intracellular signaling pathways linked to activation of M-2- and M-3-mACh receptor subtypes. The intracellular cyclic AMP accumulation and [H-3]-inositol phosphates content were measured in myometrium strips from rats in estrus (control) and estradiol-treated rats (12.5 mu g/100 g body weight, sc, 24 h before experiments) (the plasma estradiol level was 30.9 +/- 3.5 pg/ml and 119.3 +/- 14.1 pg/ml from control and estrogen-treated rats, respectively). Estrogen treatment increased 2.5-fold the intracellular cyclic AMP accumulation induced by 10 mu M forskolin. The effects of muscarinic agonist and antagonists on cyclic AMP accumulation were tested. Carbachol reduced the forskolin-induced intracellular cyclic AMP content, 3.0 and 10.5-fold, in myometrium from control and estradiol-treated rats, respectively. This inhibitory effect failed to occur when carbachol was incubated in the presence of methoctramine. Carbachol also induced increase on total [H-3]-inositol phosphates accumulation in myometrium from estradiol-treated rats when compared with control rats. This effect was reversed by pfHHSiD. These studies suggest the modulation by estrogen of intracellular signaling pathways linked to activation of M-2- and M-3-mACh receptors in the rat myometrium. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.