Meeting Abstract
Mother’s milk contains numerous hormonal constituents but the magnitude, sources, and consequences of inter-individual variation remain largely unexplored. Here we report our investigation of milk prolactin (PRL) across lactation and as a function of maternal and infant characteristics. Milk samples were collected from 85 Rhesus macaque mothers at early, peak, and late lactation. Subjects were housed in the outdoor breeding colony at the California National Primate Research Center in Davis, CA. Using standard parallelism and recovery tests, we validated enzyme immunoassays to measure PRL in mother’s milk. PRL concentration (ng/ml) was negatively correlated with milk fat (%) and protein (%) and gross energy density (kcal/g, GE). PRL was positively correlated with milk yield as we predicted given its integral role in lactogenesis. Interestingly, at the early lactation time-point, mean PRL concentration was highest (mean = 12.67 ± 0.44) and was significantly higher in milk produced for daughters (mean = 13.52 ± 0.64) than in milk produced for sons (mean = 11.78 ± 0.59) indicating sex-differentiated milk synthesis. Neither maternal parity nor maternal body mass were predictive of milk PRL concentrations, which was unexpected given that higher parity and heavier mothers in this population typically produce more milk. Similarly, milk PRL was not associated with infant body mass after controlling for milk yield and GE. These results suggest that the absolute quantity of milk PRL does not independently contribute to infant body mass. However, high concentrations and sex-differentiation of PRL during early lactation, when hormones may be most readily absorbed across the GI tract of the infant, may affect other physiological systems.
