PROSTANOID-INDUCED CONTRACTION OF THE RABBIT ISOLATED UTERUS IS MEDIATED BY FP RECEPTORS

Natural and synthetic prostanoid agonists were used to study the prost anoid receptors involved in contraction of the mature, isolated uterus of virgin rabbits. The prostanoids elicited contractile responses wit h a Yank order of potency of PGF(2)alpha, fluprostenol > PGD(2) > U-46 619 > PGE(2) > carbaprostacyclin with mean EC50 (nM) values of 4, 6, 3 4, 550, 1318 and >10,000, respectively. Carbachol, a muscarinic agonis t given after the prostanoids to elicit a reference contraction, had a mean EC50 value of 1.1 mu M. The results show that the mature rabbit uterus is most sensitive to prostaglandin FP agonists and, thus, can b e defined pharmacologically as an FP receptor preparation. These findi ngs may facilitative investigations into the possibility of different prostanoid receptor populations. In the absence of useful competitive FP receptor antagonists, agonist potency data is particularly useful i n systems where cross-species comparisons and tissue-related factors a re not involved. The potent activities of the FP agonists, PGF(2)alpha and fluprostenol, in the isolated jugular vein and uterus of the rabb it suggest that these tissues may be useful for intra-species comparis ons.