Analysis of molecular heterogeneity of prolactin in human systemic lupus erythematosus

Hyperprolactinemia without clinical manifestations has been reported in some patients with systemic lupus erythematosus (SLE) because an increase of prolactin (PRL) is produced due to the BIG/BIG molecular variant (molecular variant < 150 kD). This research project aimed to determine levels of PRL: its bioactive form, the little nonglycosylated form (NGPRL) and variants with decreased bioactivity such as the BIG/BIG and the little glycosylated (GPRL), in 29 women and five men with SLE. PRL was assayed by IRMA with a kit from Immunotech Laboratory, the BIG/BIG form by precipitation with polyethyleneglycol 6000, and the NGPRL and GPRL by chromatography on Concanavalin-A- Sepharose. Increased PRL was detected in seven patients (20.6%) of whom three had increased BIG/BIG, six had increased GPRL and only four had increased NGPRL. The three cases with increased BIG/BIG were contrasted by chromatography on Sephadex G-100. No increased PRL or any of the other variants assayed were found in men. Results were similar when PRL was evaluated in the same blood samples by a different IRMA (DPC Laboratory). The etiology of the hyperprolactinemia in some of these patients is unknown, but their lack of symptoms (galactorrhea or amenorrhea) could be due to the BIG/BIG forms and basically to the glycosylation of the hormone. As for the relation between PRL and SLE activity, we found that hyperprolactinemic patients were younger, had a shorter history of illness, although it was not statistically significant, and a higher SLEDAI score. This would indicate a relation between hyperprolactinemia and lupus activity. The patients with increased BIG/BIG form also had a very active illness at the time of the study.