Relation of plasma oxytocin and prolactin concentrations to milk production in mothers of preterm infants: Influence of stress

Responses of oxytocin and PRL to mechanical breast pumping and the influenc e of physiological indicators of stress were measured at 2, 4, and 6 weeks postpartum to determine potential causes of inadequate milk production in 1 8 women with prematurely delivered, nonnursing ((<1500 g) infants. Median m ilk production was similar to that reported in breastfeeding mothers, but a third of mothers were producing less than half as much by week 6. Plasma o xytocin was similar to that previously reported for breastfeeding mothers. The oxytocin area under the curve (AUC) for breast-pumping sessions (70 min ) was correlated at each occasion (r = 0.37, 0.58, and 0.55, respectively) with milk yield. Unlike reports of PRL levels in breastfeeding women, PRL A UC declined between weeks 2 and 6 weeks postpartum (P = 0.03); significant increases in plasma PRL occurred in response to pumping at 2 and 4 weeks, b ut not at 6 weeks. Salivary amylase, a measure of a-adrenergic activity, wa s highly negatively correlated on each occasion with PRL AUC (r = -0.58, -0 .68, and -0.86, respectively), but not with oxytocin. Salivary cortisol was negatively correlated to a lesser degree. We hypothesize that deficiencies in preterm lactation are mediated in part upon stress-induced suppression of PRL secretion through an adrenergic mechanism.