Serum Prolactin Concentrations in the Adrenalectomized Rat: Relationships to Puberty Onset

Abstract

The purpose of this study was to examine the hypothesis that prolactin is involved in puberty onset by comparing changes in serum prolactin (PRL) concentrations between weaning age and puberty in normal rats and in rats in which puberty was delayed by means of adrenalectomy at 22 days of age. In intact rats a consistent elevation in serum PRL was observed between 28 and 30 days of age (a rise from a mean of 8.4 .+-. 1.4 ng/ml PRL to 24.6 .+-. 2.4 ng/ml PRL). After adrenalectomy at 22 days of age there was a depression of PRL lasting several hours. This was followed by an elevation which persisted for the next 48 h. The PRL elevation observed in intact rats between days 28-30 was absent in rats adrenalectomized at 22 days of age. Associated with the absence of the elevation in serum PRL, there was a delay in vaginal opening and ovulation of 4-5 days. Replacement therapy with corticosterone in the drinking water (80 .mu.g/ml) resulted in normal vaginal opening and ovulation times but failed to restore the prolactin elevation, and suppressed the early rise in serum prolactin during the first 2 days after adrenalectomy. At 34 and 36 days of age, adrenalectomized rats had higher serum PRL levels than controls and subsequently both groups maintained high PRL except at 41 days of age when control PRL levels again fell. It seems likely that the prepubertal PRL elevation (days 28-30) is not required per se for puberty since puberty was normalized in adrenalectomized rats maintained on corticosterone despite the absence of the PRL elevation. It is possible that corticosterone substitutes for the effects of the prepubertal prolactin rise.