Identification of functional high and low affinity states of the prostaglandin F2 alpha receptor in the ovine corpus luteumin vivo and their role in hormone pulsatility

Equivocal evidence has accumulated for the presence of high and low affinity receptors for PGF(2α) in the corpus luteum based on binding affinities of(3)H-PGF(2α) to cell membranes or separated whole cells. Some studies report only high affinity sites, while others report the occurrence of both high and low affinity sites. We have previously demonstrated, using subluteolytic levels of PGF(2α), the existence of functional high affinity luteal PGF(2α) receptors which show desensitization and recovery after 6 to 9 h. The present study, using direct intra-arterial infusions of PGF(2α) into the autotransplanted ovary in conscious sheep, was designed to probe for the existence of functional high and low affinity states of the PGF(2α) receptor in the corpus luteumin vivo. Subluteolytic and luteolytic concentrations of PGF(2α) (100 pg/min and 2500 pg/min, respectively) were infused sequentially, each for 2 h, into the ovary during the luteal phase (n=7 sheep). The same low and high concentrations of the inactive metabolite of PGF(2α) (PGFM) were given over the same time periods as negative controls (n=4 sheep). During the 2 h intra-arterial infusion of 100 pg/min of PGF(2α) the secretion rate of oxytocin increased (P