Interaction of prostaglandin E2 and beta-adrenergic catecholamines in the regulation of uterine smooth muscle motility and adenylate cyclase in the rat.

Prostaglandin E2 (PGE2) increased the force of the spontaneous contractions of the rat myometrium and decreased the sensitivity of the uterus to the relaxing effects of the specific beta-adrenergic catecholamine agonist isoprenaline. Prostaglandin E2, at concentrations above 10 mumol/l, increased cyclic AMP production by intact muscle strips. The muscle strips were far more sensitive, however, to the inhibitory effect PGE2 had on isoprenaline-dependent cyclic AMP production (threshold less than 0.001 nmol/l). Both PGE2 and isoprenaline stimulated adenylate cyclase activity of a myometrial subcellular (particulate) fraction in a guanyl nucleotide-requiring manner. When present in saturating concentrations (100 mumol/l), the stimulatory effects were not additive, suggesting that the receptors for the two agonists competed for the same catalytic subunit of adenylate cyclase or for the same guanyl nucleotide-requiring factor which couples receptors and enzyme. If muscle strips were incubated with PGE2 before the preparation of the adenylate cyclase-containing particulate fraction, the enzyme became less responsive to stimulation by guanyl nucleotide and by isoprenaline and PGE2 in the presence of guanyl nucleotide. The PGE2 receptor may therefore interact with the beta-adrenoreceptor to inhibit isoprenaline-dependent cyclic AMP production by intact muscle cells by desensitizing adenylate cyclase, possibly at the level of the guanyl nucleotide-dependent coupling step.