Effects of gonadotrophins, hypophysectomy and prostaglandin F-2 alpha on corpora lutea and ovarian follicles, and evidence for the presence of PGF-2 alpha receptors in the ovarian follicles and interstitium of non-pregnant guinea-pigs.

Simultaneous administration of hCG (but not FSH or prolactin) with PGF-2 alpha prevented the luteolytic effect of PGF-2 alpha after Day 9 of the oestrous cycle both morphologically and in terms of progesterone secretion in hysterectomized guinea-pigs. Hypophysectomy on Day 5 or PGF-2 alpha administration on Days 6--9 were not luteolytic, but their combined effect resulted in an advanced state of luteolysis as early as Day 9. When PGF-2 alpha was injected simultaneously with FSH or prolactin (but not hCG), the proportion of atretic antral follicles was significantly increased, although the total number of antral follicles remained unchanged. When PGF-2 alpha receptors were measured in the membrane fractions of luteal tissue and ovarian stromal, interstitial and follicular tissue obtained from cyclic animals, the concentrations were 22.75 and 36.26, and 62.60 and 96.26 fmol/mg membrane protein on Days 5 and 12, respectively. It is concluded that (1) LH protected corpora lutea against the luteolytic action of PGF-2 alpha up to Day 9 of the cycle, (2) PGF-2 alpha receptors were present in follicles, and (3) these receptors and PGF-2 alpha were involved in the development of the normal complement of Graafian follicles.