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Glycosylated and Nonglycosylated Prolactin in Serum During Pregnancy^*

Lutcher Brown Department of Biochemistry, Whittier Institute for Diabetes and Endocrinology (E.M., D. W.L.) La Jolla, California 92037
The Department of Reproductive Medicine, University of California School of Medicine (D.R.H.) San Diego, California 92093

Address all correspondence and requests for reprints to: Edith Markoff, Ph.D., The Whittier Institute for Diabetes and Endocrinology, 9894 Genesee Avenue, La Jolla, California 92037.

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-µL aliquots of serum, and the precipitates were subjected to gel electrophoresis n i 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.

^* This work was supported by NIH Grants DK-35679, HD-19094, HD-13469, BRSG S07-RR-05876 to the Whittier Institute and NIH Grant RR-0827 to the UCSD Clinical Research Center. Presented in part at the 69th Annual Meeting of The Endocrine Society, Indianapolis, IN, June 1987.

Received September 4, 1987.