Estrogen and the puberty-advancing effect of hyperprolactinemia in female rats

Female Wistar rats were twice daily injected with 10 IU prolactin from 21 days of age to vaginal opening (VO). Precocious VO and ovulation followed by an ovarian cycle of normal length were recorded following this treatment. Hyperprolactinemia induced by the implantation of one pituitary under the kidney capsule of 23-day-old females resulted in advancement of VO but, probably due to the antiovulatory and luteotropic effects of the permanently elevated prolactin levels, the first ovulation occurred only at the normal time of puberty onset, and the first ovarian cycle was significantly lengthened. An increase uterine but not of ovarian weight was induced by both treatments indicating enhanced estrogen secretion. Daily injections of 0.05 or 0.1 microgram estradiol benzoate per 100 g b.w. administered during different periods between day 21 and VO, however, were ineffective in accelerating sexual maturation. The findings suggest that the puberty-advancing effect of hyperprolactinemia does not primarily depend upon the stimulation of ovarian estrogen secretion.