Prostaglandin F2 alpha inhibits luteinizing hormone (LH)-induced increase in LH receptor binding to isolated rat luteal cells.

The effect of the luteolytic hormone prostaglandin F2 alpha (PGF2 alpha) on parameters of LH receptor binding to isolated rat luteal cells was examined. The equilibrium binding constant (0.55 X 10(10) M-1), the association rate constant (0.89 X 10(8) M min-1), and the dissociation rate constant (1.70 X 10(-2) M min-1) were not significantly altered by PGF2 alpha. However, as [125I]iodohCG binding approached equilibrium (less than 2 h) and at equilibrium (greater than 3 h), PGF2 alpha, but not PGE2, consistently reduced LH binding by 10-20%. The LH receptor-binding capacity, determined by Scatchard analysis of [125I]iodo-hCG or [125I]iodo-hLH binding, was reduced from 7.5 +/- 0.1 to 6.4 +/- 0.1 X 10(4) receptors/cell in the presence of PGF2 alpha. This reduction of total cell-bound radioactivity by PGF2 alpha was not due to a change in the rate of hormone internalization and degradation. However, when cells were briefly treated with a pulse of LH (5 ng/ml; 5-10 min), [125I] iodo-hCG (LH) binding increased 20-30% within 2 h, and PGF2 alpha prevented this LH-induced increase. A similar pulse of cAMP analogs did not alter LH binding. We conclude that while the initial binding of LH to its receptor is not altered by PGF2 alpha, it does reduce the final equilibrium level of LH binding by a mechanism that involves a block in the appearance of LH-induced cryptic receptors.