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Biphasic effects of moderate drinking on prolactin during lactation.

BACKGROUND
Contrary to the popular lore that encourages women to drink alcohol as an aid to lactation, we previously showed that alcohol consumption disrupted lactational performance and the hormonal milieu of the lactating mother in the short term.


METHODS
Thirteen lactating women participated in a 4-session, double-blind, 2 x 2 within-subject study to test several hypotheses related to the effects of alcohol on prolactin (PRL) responses and milk yield over time. The two within-subject factors were beverage condition (control or 0.4 g/kg dose of alcohol) and pumping condition (pumping occurred at fixed intervals once or twice during the 5.3-hour session). Plasma PRL, blood alcohol concentrations (BAC), and milk yield were measured.


RESULTS
Alcohol consumption increased basal PRL levels (p < 0.0001) and modified the PRL response to pumping (p < 0.0001) but the directionality of the response depended on when pumping occurred along the BAC curve. Pumping enhanced PRL response when it occurred during the ascending BAC limb but blunted the response when it occurred during the descending limb, providing evidence that the effects were transient and of a biphasic nature. The slower the alcohol was metabolized, the greater the relative PRL response to breast pumping (p < 0.05). The dynamics of the PRL response between pumping sessions was also altered if women drank. If women pumped within the hour after drinking alcohol, the PRL response during the next pumping some 1.5 hours later, was delayed by a few minutes. Milk yield was significantly lower after drinking alcohol but such deficits were not significantly related to PRL or the speed at which alcohol was eliminated.


CONCLUSIONS
Effects of alcohol on suckling-induced PRL were biphasic in nature, but could not explain the deficits in lactational performance. Such findings provide further evidence that the dynamic changes in neuroendocrine state are integrally involved in alcohol's effects over time and underscore the complexity of lactation.