Induction of luteinized unruptured follicles in the rat after injection of luteinizing hormone early in pro-oestrus.

The cause of formation of luteinized unruptured follicles (LUF) is unknown. Formation of LUF was studied after injection of a varying small dose of luteinizing hormone (LH) with or without subsequent injection of gonadotrophin-releasing hormone (GnRH); in addition, the effect of suppression of prolactin on LUF formation was studied. Luteinization without ovulation occurred in virtually all graafian follicles, if 0.5-1.0 microgram of LH was injected some hours before the presumed endogenous LH surge (suppressed by Nembutal); with increasing doses of LH progressively increasing numbers of ovulations were observed. If an early pro-oestrus 1 microgram of GnRH was given 4 h after 1 microgram of LH, formation of LUF was partly prevented; if the interval between LH and GnRH was 8 h or more, the great majority of graafian follicles developed into LUF. If early in pro-oestrus 1 microgram of LH was given and 8 h later 0.1 microgram of a potent GnRH analogue, about 50% of the follicles became LUF; in similarly treated rats, suppression of prolactin by ergocryptine reduced but did not prevent LUF formation. The data support the idea that deficient LH secretion in the period before ovulation may be involved in the formation of LUF.