INDUCTION OF OVULATION IN THE GUINEA-PIG

Abstract

SUMMARY Ovulation has been induced in the cyclic guinea-pig at a time when the ovaries contain mature follicles, by a single injection of purified luteinizing hormone (LH), follicle-stimulating hormone or guinea-pig gonadotrophins from homogenates of female guinea-pig anterior pituitaries. An injection of any one of the substances given too early only caused follicular luteinization and the ova were retained, even with increased dosage. A single injection of LH in mid-dioestrus caused 'LH effects' on the follicles (destruction of the growing follicles), giving a histological picture similar to that which obtains at the time of ovulation in the untreated animal. Homogenates of anterior pituitaries taken from donor guinea-pigs 1–2 days before ovulation was due (but not at any other time in the cycle) when injected into recipients at middioestrus had similar effects on the follicles. Donor anterior pituitaries taken from guinea-pigs in which ovulation had been inhibited by daily injections of progesterone, caused ovulation in recipients with mature ovarian follicles or 'LH effects' in those in mid-dioestrus. It is suggested that in the guinea-pig there is a basal secretion of gonadotrophins during most of the cycle. A day or two before ovulation occurs and when the ovaries already contain ripe follicles, there is a marked increase in the synthesis of LH which is then released from the anterior pituitary gland and rupture of the follicles occurs.