Characteristics of receptors for prostaglandin F-2 alpha in bovine and equine corpora lutea.

Prostaglandin F-2 alpha (PGF-2 alpha) receptors of bovine and equine corpora lutea (C.L.) were studied. From both the equilibrium binding data and the dissociation kinetics behaviour, two affinity classes of receptors are evident in the mare, with apparent dissociation constants (Kd) of 1,5 x 10(-9) M and 3.5 x 10(-8) M. Bovine PGF-2 alpha receptors present a homogeneous population of binding sites with Kd = 1 x 10(-8) M. Both bovine and equine C.L. receptors bind PGF-2 alpha in a specific manner; only 13, 14-dihydro-PGF-2 alpha considerably cross-reacts with these receptors. Since in the mare uterine PGF-2 alpha reaches the ovary systemically with consequent extensive degradation, it is suggested that this metabolite could act as a luteolysin in this species. The dissociation kinetics indicate that the hormone-receptor (H-R) reaction evolves from a state of loose binding to one of tight binding as the time of incubation proceeds. This could be explained by internalization of the H-R complex.