Interaction of prostaglandin E 1 and calcium in the guinea-pig myometrium.

1. Prostaglandin E(1) (PGE(1)) increased the responses of guinea-pig myometrium in a low calcium medium to added Ca(2+), acetylcholine, vasopressin, Ba(2+) and Sr(2+). The concentration of PGE(1) used (50 pg/ml) was clearly below the threshold for direct spasmogenesis. In the presence of PGE(1) the doses necessary for half-maximal contractions were decreased by factors of 2.6 for Ca(2+), 2.4 for acetylcholine, and 3.7 for vasopressin. The responses to Ba(2+) or Sr(2+), though studied less extensively, were found to be affected in much the same manner.2. The K(+) depolarized myometrium in a low Ca(2+) medium contracts in response to added Ca(2+). These responses also were increased by low concentrations of PGE(1), but the effective concentration of PGE(1) was indistinguishable from that for direct spasmogenesis.3. Possible mechanisms for the interaction of PGE(1) and Ca(2+) in the myometrium are discussed. It is tentatively suggested that these findings may be relevant to the physiological control of human myometrium.