Glycosylated and nonglycosylated prolactin in serum during pregnancy.

To study the pattern of release of glycosylated (G-PRL) and nonglycosylated (PRL) under various physiological conditions, we studied normal women from the first trimester of pregnancy through the postpartum period. Immunoreactive PRL variants were immunoprecipitated from 100-microL aliquots of serum, and the precipitates were subjected to gel electrophoresis in the presence of sodium dodecyl sulfate, electrotransferred to nitrocellulose paper, immunoblotted with anti-PRL serum and [125I]protein-A, and autoradiographed. The relative concentrations of the two forms of PRL were indicated by the intensity of the electrophoretic bands. Before pregnancy, serum G-PRL was the predominant PRL form. As pregnancy progressed, increasing amounts of PRL, compared to G-PRL, appeared in the serum, and it reached a maximum by the third trimester. G-PRL was found at all stages of pregnancy, even when the amount of PRL was greatest. After parturition in nonnursing mothers the PRL band again decreased; however, in nursing mothers the PRL band remained prominent. We conclude that the G-PRL and PRL variants may fulfill different physiological roles and, under certain conditions, such as pregnancy and lactation, more of the nonglycosylated PRL may be produced to fill special requirements.