Prostaglandins, thromboxanes and the pregnant rat uterus at term.

1 Prostaglandin and thromboxane release from the term pregnant (Day 22) rat uterus in vitro has been measured by radioimmunoassay and gas chromatography combined with mass spectrometry. 2 Prostacyclin (prostaglandin I2, PGI2) and thromboxane A2 (TXA2) (measured as their metabolites, 6-oxo-PGF1 alpha and TXB2, respectively) were released in large amounts, while PGE2 and PGF2 alpha were released in smaller amounts. PGD2 was released in the largest quantities. 3 Treatment of the term pregnant rat uterus in vitro with the PGI2 synthesis inhibitors, 15-hydroperoxy arachidonic acid (15-OOH AA) and tranylcypromine caused spasm of the tissue. 4 15-OOH AA caused dose-dependent increases in prostaglandin release, while tranylcypromine caused a fall in the release of PGE2 but did not affect the release of other prostaglandins. A possible reason for the effect of 15-OOH AA on prostaglandin release is discussed. 5 Indomethacin prevented spontaneous activity of the term pregnant rat uterus in vitro. Contractions were restored by prostaglandins and their order or potency was PGE2 greater than PGF2 alpha greater than PGI2 greater than PGD2 much greater than 6-oxo-PGF1 alpha = TXB2.