Heterogeneity of serum and amniotic fluid prolactin in humans

The molecular heterogeneity of PRL was studied in serum and amniotic fluid using immunoperoxidase electrophoresis. In the amniotic fluid, larger molecular variants (greater than 117 kD), small PRL (20 and 23 kD) and cleaved PRL were present in the nonreduced condition. Newly, three mercaptoethanol (MCE)-resistant forms (76, 64 and 53 kD), and 25- and 23-kD forms appeared after treatment with MCE. Two variants, 64 and 23 kD, did not bind to concanavalin A (Con A), indicating a simple peptide without sugars. Other glycosylated forms, 76, 53 and 25 kD, bound to Con A. In maternal serum, the same components as those in the amniotic fluid were seen, except for a scanty amount of 23 kD and a newly appearing glycosylated variant of 28 kD in the reduced condition. This 23-kD form also appeared with the administration of TRH in women.