Change in electrophoretic mobility of human follicle-stimulating hormone in serum after administration of gonadotropin-releasing hormone.

The median electrophoretic mobility of FSH in serum (S-FSH) was determined in 14 girls, aged 9-14 yr, with Turner's syndrome before and after iv administration of GnRH. The basal S-FSH level varied almost 100-fold between patients. Less negatively charged forms of FSH appeared in serum in all patients after GnRH stimulation. The aim of the study was to determine if the change in electrophoretic mobility of S-FSH after GnRH treatment was related to the basal S-FSH level, the absolute or relative increase in the S-FSH level after GnRH, or the electrophoretic mobility of S-FSH present in the basal state. A highly significant (r = 0.94; P less than 0.001) correlation was found between the relative increase in S-FSH 60 min after GnRH treatment and the decrease in electrophoretic mobility. A selective survival of different forms of FSH in the circulation is proposed as the most likely explanation for the appearance in serum of the less negatively charged forms of FSH after GnRH stimulation.