Failure of maintained hyperprolactinemia to improve lactational performance in late puerperium

Although stimulation of PRL secretion in the early postpartum period has been found to improve lactational performance, the effect of chronic maintenance of elevated plasma PRL levels on milk production is not known. In a randomized design, 66 lactating women were assigned to receive either a placebo (n = 32) or the dopamine antagonist sulpiride (n = 34; 100 mg, three times daily), for 4 days, followed by 50 mg, three times daily, for a 90-day period). Their basal and 30 min postsuckling plasma PRL levels as well as the weights of their infants were measured 1, 4, 15, 30, 60, and 90 days postpartum. Forty-one women (20 sulpiride-treated and 21 placebo-treated) completed the study. Compared with the placebo group, which had the expected postpartum plasma PRL decline, the sulpiride-treated women maintained significantly elevated basal plasma PRL values up to the 90th postpartum day. In contrast, the postsuckling plasma PRL level was significantly diminished in the latter group, and on day 90 was practically absent. On day 15, weight gain was significantly greater in the infants whose mothers received sulpiride, but later, no differences were detectable between groups of infants despite the disparity in PRL levels in their mothers. We conclude that enhancement of PRL secretion in the early postpartum period may transiently increase milk production, but chronic hyperprolactinemia has no effect on lactational performance. The plasma PRL response to suckling is not essential for the maintenance of milk secretion. Instead, basal plasma PRL levels and neurogenic reflexes may be more instrumental in maintaining established lactation.