Characterization of specific prostaglandin E receptor in isolated rat Leydig cells

The binding of 3H-prostaglandin E1 (PGE1) to the isolated Leydig cells from rat testes was studied under different experimental conditions. The Scatchard plot analysis showed two populations of specific binding sites: one of a high affinity and low capacity (Ka1 = 2.2 x 10(8) mol-1 l) and the other with less affinity and high capacity (Ka2 = 8.7 x 10(7) mol-1 l). Maximum specific binding occurred at pH 7.4 and 22 degrees C. Unlabelled PGE1 and PGE2 inhibited the binding in a dose-dependent manner, while about 10 times higher amount of PGA1 was necessary to show a similar effect. Moreover, the treatment of Leydig cells with disulfide modifying agents (dithiotreitol and mercaptoethanol) decreased 3H-PGE1 binding. Finally, the production of cAMP was 4.5 times increased (P less than 0.001) after 20 min incubation of Leydig cells with PGE1 and aminophylline, while that of testosterone was 2.5 times increased (P less than 0.001) after 3 h incubation with PGE1.