Activation of adenylyl cyclase in human myometrial smooth muscle cells by neuropeptides

The levels of intracellular cAMP in human myometrial smooth muscle cells in serum-free medium, or medium that contained FBS (1%, vol/vol), were determined after treatment with the homologous peptides, calcitonin gene-related peptide (CGRP), adrenomedullin (ADM), and amylin, without or with added isobutylmethylxanthine (IBMX). These cells were sensitive to CGRP, responding in a dose-dependent manner, with maximal levels of cAMP being attained with 5 nM CGRP in the presence of IBMX (1 mM). In the absence of IBMX, the level of cAMP attained in cells treated with CGRP (5 nM) (675.3 +/- 58.8 pmol.mg protein.15 min; mean +/- SEM, n = 3) was approximately 90 x that in nontreated cells (7.5 +/- 0.4 pmol.mg protein.15 min). The level of cAMP in myometrial cells treated with CGRP (5 nM) + IBMX (1 mM), 1998 +/- 420 pmol.mg protein.15 min, was 29x that in cells treated with IBMX alone (69.2 +/- 10.2). The maximum level of cAMP achieved by treatment with ADM + IBMX was similar to that with CGRP + IBMX, but the dose of ADM required (1 mu M) was approximately 200x that of CGRP. Amylin amide also caused an increase in cAMP but with considerably less potency; at a concentration of 500 nM, amylin amide + IBMX effected a 2.3-fold increase in cAMP relative to IBMX alone. CGRP(8-37), an antagonist of CGRP via the CGRP, receptor, inhibited the action of CGRP, ADM, and amylin in myometrial cells. Treatment with [cys(ACM)(2-7)]-CGRP, a CGRP(2) receptor agonist, did not cause an increase in the levels of cAMP in these cells. These findings are indicative that CGRP, ADM, and amylin act via that the CGRP, receptor in human myometrial cells. Vasoactive intestinal peptide and pituitary adenylate cyclase activating polypeptide also caused a dose-dependent increase in cAMP in myometrial cells. The findings of this study are indicative that multiple neuropeptides, acting by way of heptahelical receptors linked to the Ga,subunit of the G-proteins, may contribute to the maintenance of uterine quiescence during some period of human pregnancy.