Molecular heterogeneity of circulating prolactin in chronic uremic men and renal transplant recipients

Serum PRL levels and its molecular heterogeneity were analyzed, basally and after 500 micrograms TRH given acutely, in four groups of men: normal (C, n = 12), chronic renal failure (CRF, n = 11), hemodialysis (HD, n = 12), and transplant recipients (T, n = 11). The mean basal PRL level was higher in group CRF than in group C and even higher in group HD. The basal hyperprolactinemia was due to increased concentrations of little PRL. The absolute levels of total and little PRL 20 min after TRH were comparable in the four groups. The disappearance index (DI = PRL20-PRL120/PRL20) for total and little PRL was lower in CRF than in C and even lower in HD. A positive correlation was found between the DIs of total and little PRL and creatinine clearance in group CRF. Group T had basal and 20 min serum PRL levels and a pattern of molecular distribution similar to those of group C but total and little PRL DI was lower. These results demonstrate that uremic hyperprolactinemia is due to increases in little PRL without major changes in big and big-big forms of PRL. The reduction of glomerular filtration rate seems to be one of the most important mechanisms responsible for little PRL accumulation.