Further Evidence that Prolactin Controls the Prepubertal Sexual Development in the Female Rat

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Abstract
To assess the role of prolactin (PRL) in the puberty onset and the ovarian aromatase activity, hyper- and hypoprolactinemic conditions were induced by treating chronically prepubertal female rats with PRL and bromocriptine, respectively. Injection of rat PRL (5 µg, twice daily) from day 20 onward advanced the day of vaginal opening. By contrast, the suppression of PRL release by bromocriptine, which was provided in the drinking water at a concentration of 40 µg/ml, caused a significant delay in the age of occurrence of vaginal opening. This bromocriptine-induced delayed puberty was prevented by the concomitant administration of exogenous PRL, suggesting that the effect of bromocriptine is exerted through its suppressive effect on the endogenous PRL release. The in vitro release of estradiol by the ovaries from 30-day-old rats treated with PRL was found to be higher than that from the control animals, when the ovaries were perifused for 6 h with an excess of androstenedione. On the other hand, the ovaries perifused in the presence of androgen produced less estradiol in the bromocriptine-treated rats than in their controls. It appears, therefore, that PRL is more likely related to the aromatase activity in the maturing ovary. These results suggest that PRL may be one of the factors that regulate the timing of puberty onset by influencing the aromatase activity in the ovary.