Depriving neonatal rats of milk from early lactation has long-term consequences on mammotrope development.

The sudden appearance of prolactin-releasing cells during the early postnatal period of the rat is initiated by a small milk-borne peptide. Depriving newborn rats of this early milk factor severely retards mammotrope differentiation during the neonatal period. In the present work, we extend our study of early milk deprivation to the adult. To this end, newborn litters were crossfostered onto mothers that had given birth the same day or one week earlier in order to deprive pups in the latter group of early milk. At 5, 15, and 30 d of age, rats deprived of such milk had decreased percentages of mammotropes (as measured by reverse hemolytic plaque assay, RHPA) when compared to nondeprived animals (P < 0.05). By 45 d, the percentage of mammotropes was similar for the two crossfostered groups (P > 0.1) and this persisted through d 60. Subsequently, we assessed the secretory capacity of mammotropes from 60-d old rats to secretagogues and found that early milk deprivation had no effect on basal prolactin release (P > 0.1), but that it augmented hormone secretion evoked by thyrotropin-releasing hormone (TRH, 100 nM; P < 0.01). The inhibitory response to dopamine (DA; 1 microM) and the stimulatory response to angiotensin II (AGII; 100 nM) were not altered by early milk deprivation (P > 0.1). Taken together, these results demonstrate that factors in milk from early lactation are required for normal mammotrope differentiation, and that the delay induced by early milk deprivation leads to altered secretory function of mammotropes in adult animals.