Ontogeny of prolactin secretion in the neonatal rat is regulated posttranscriptionally.

PRL-secreting cells first appear in appreciable numbers on day 4 of neonatal life in rats. In the present study, we attempted to ascertain whether the ontogenic appearance of PRL mRNA and hormone release were temporally coordinated or discordant. Our results show that the PRL gene is expressed at least 3 days before the onset of secretion in newborn rats. Moreover, steady state levels of PRL mRNA in neonates are at least as high as those found in 10-day-old rats, in which 15-17% of all pituitary cells secret the hormone. This apparent blockage of translation is attributable to a lack of association of PRL message with ribosomes in the neonate. Taken together, these data indicate that the ontogeny of PRL secretion in rats is regulated translationally as well as transcriptionally.