Pu Isatile Infusion of Lutein izing Hormone-releasing Hormone Induces Precocious Puberty (Vaginal Opening and First Ovulation) in the Immature Female Guinea Pig1

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Abstract
Previously we have hypothesized that an increase in luteinizing hormone-releasing hormone (LHRH) due to hypothalamic maturation is the key factor controlling the onset of puberty. This led to the working hypothesis that precocious puberty would be induced if LHRH is administered with an appropriate protocol. Thus, effects of pulsatile infusion of LHRH on the onset of first vaginal opening and first ovulation in immature female guinea pigs were studied. Luteinizing hormone-releasing hormone in hourly pulses of either 5 ng or 50 ng was infused through a chronically implanted jugular catheter for 9-29 days starting at 20 days of age. For the control experiment saline was infused in a similar manner. Infusion of 5 ng LHRH/h resulted in significantly earlier (P < 0.001) ages at first vaginal opening (24.7 .+-. 0.9 days) and at first ovulation (28.8 .+-. 0.9 days) compared to saline controls (first vaginal opening 53.3 .+-. 6.8 days; first ovulation 55.2 .+-. 6.5 days). Infusion with a 10-fold higher LHRH dose (50 ng/h) also advanced the age at first vaginal opening (25.3 .+-. 0.7 days), but precocious ovulation was no longer induced (53.7 .+-. 5.3 days). Interestingly, LHRH infusion with the high dose resulted in a prolonged period of vaginal opening and cornification without ovulation. These results indicate that (1) pulsatile infusion of a small amount of LHRH with a constant frequency induces precocious puberty in a laboratory rodent, and (2) infusion of LHRH with a dose higher than the effective dose for the induction of early puberty results in a persistent estrous anovulatory syndrome. Therefore, the present study not only supports our hypothesis that an increase in endogenous LHRH release is responsible for the onset of puberty, but also further suggests that excessive release of LHRH or abnormal patterns of LHRH release may be involved in the etiology of the anovulatory persistent estrus syndrome.