Studies on the Time of Luteinizing Hormone Release in Gonadotrophin-Treated Immature Rats

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Abstract
The ovulatory response of immature Wistar rats to a single injection of pregnant mares′ serum gonadotrophin (PMS) was determined. Nembutal (sodium pentobarbitone, 45 mg/kg) prevented ovulation when given 54–55 hr after PMS among animals injected with PMS at the beginning of a light period. Ovulation occurred sooner after PMS in animals given the injection at the beginning of a dark period; Nembutal injection 42–43 hr after PMS in this group blocked the ovulatory response. The evidence from both groups suggests that luteinizing hormone (LH) was released at about 8 hr after the onset of the second period of light following PMS administration. When animals were reared in constant illumination, many failed to ovulate in response to PMS; litter mates reared in constant light and given human chorionic gonadotrophin 56 hr after PMS did ovulate. PMSinduced ovulation in the 27-day-old rat in the colony studied appears to be dependent on neural mechanisms which may be activated according to the prevailing pattern of light and dark periods. (Endocrinology76: 958, 1965)