Delay of Puberty Onset in Females due to Suppression of Growth Hormone*

Abstract

To determine whether suppression of GH and/or PRL in the presence of normal growth rates would affect the timing of puberty onset, weanling rats were infected with plerocercoid larvae of the tapeworm Spirometra mansonoides. Plerocercoid growth factor, which is released by S. mansonoides, stimulates growth while depressing endogenous GH. Vaginal opening and ovulation were significantly delayed in infected animals compared to those in untreated or vehicle-injected controls (P < 0.01). Although growth rates were comparable in all three groups, plerocercoid-treated (10 plerocercoids/rat) animals showed significantly depressed circulating PRL levels at 26 days of age but not at 32 days of age, and depressed GH levels at both ages. Vaginal opening and, to a lesser extent, ovulation could be normalized in the plerocercoid-treated animals by the administration of PRL or GH or 24–26 days of age. The effects of plerocercoids and hormonal replacement were not dependent upon the adrenals. Despite normal body weight gains in infected adrenalectomized animals, puberty occurred significantly later than that after adrenalectomy alone. While the plerocercoids were able to stimulate normal growth, the similarity of action between plerocercoid growth factor and GH did not extend to influences on puberty onset. It can be concluded that puberty onset in plerocercoid-infected rats is not tightly correlated with body weight gain per se. (Endocrinology106: 1989, 1980)