Prolactin size variants during pregnancy in women with ovulatory hyperprolactinemia: characterization by isoelectric focusing and lectin affinity chromatography

Abstract

Previous studies from this laboratory have demonstrated the occurrence of important changes in PRL size heterogeneity in women with ovulatory hyperprolactinemia during gestation. A similar observation has been made, in normal women, for glycosylated PRL, which shows a progressive decrease as pregnancy progresses. In this study we decided to investigate the contribution of G-PRL on PRL heterogeneity throughout gestation in women with ovulatory hyperprolactinemia. Serum samples obtained throughout gestation were analysed by SDS-PAGE followed by immunoblotting and by isoelectric focusing of gels as well. The results indicated that, independent of the stage of pregnancy, the relative amounts of G-PRL as compared with the nonglycosylated form of the hormone remained quite constant. In addition, isoelectric focusing analyses of serum samples consistently resulted in an identical isoelectric point of PRL throughout all of the gestational period. These results suggested that changes in the relative proportions of PRL size species during pregnancy were not correlated with the degree of PRL glycosylation. Moreover, these observations further extended and supported the concept that the occurrence of PRL size heterogeneity depends mainly on thiol-disulfide interchange mechanisms, among PRL molecules, at the pituitary level.