Interaction of prostaglandin E1 and calcium in the guinea‐pig myometrium

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Abstract
1 Prostaglandin E1 (PGE1) increased the responses of guinea-pig myometrium in a low calcium medium to added Ca2+, acetylcholine, vasopressin, Ba2+ and Sr2+. The concentration of PGE1 used (50 pg/ml) was clearly below the threshold for direct spasmogenesis. In the presence of PGE1 the doses necessary for half-maximal contractions were decreased by factors of 2·6 for Ca2+, 2·4 for acetylcholine, and 3·7 for vasopressin. The responses to Ba2+ or Sr2+, though studied less extensively, were found to be affected in much the same manner. 2 The K+ depolarized myometrium in a low Ca2+ medium contracts in response to added Ca2+. These responses also were increased by low concentrations of PGE1, but the effective concentration of PGE1 was indistinguishable from that for direct spasmogenesis. 3 Possible mechanisms for the interaction of PGE1 and Ca2+ in the myometrium are discussed. It is tentatively suggested that these findings may be relevant to the physiological control of human myometrium.