INSULIN-LIKE GROWTH FACTORS AND BINDING PROTEINS IN HUMAN EJACULATES
JA Nikolic, O Nedic, N Mihailovic & I Baricevic
While previous studies have shown relatively low concentrations of insulin-like growth factors (IGF)in human ejaculates, high levels of IGF binding protein-2 (IGFBP-2)have been reported. The IGF/IGFBP system was investigated in ejaculates from thirty men aged 23-46 years consulting a fertility clinic. Volume, viscosity, total and motile sperm counts were estimated by standard methods and each subject consented for the specimen to be used in this study. Local Ethical Committee approval was obtained. Mean ejaculate volume was 3.3 ml (range 1 - 6 ml). Viscosity was increased moderately in six samples and greatly in four more. The number of motile sperm (0 - 165 million/ml; mean 49; median 39) was highly correlated with total number (P < 0.001). Concentrations of IGF-I and IGF-II determined by displacement radioimmunoassay were positively correlated (P = 0.001). IGF-I ranged from 2.7 to 29.7 nmol/l (mean 9.6; median 6.5) and increased with viscosity. IGF-II ranged from 5.7 to 39.0 nmol/l (mean 16.0; median 13.5). IGFBP-2 and putative IGFBP-4 were detected by autoradiography of ligand blots after sodium dodecyl sulphate polyacrylamide gel electrophoresis. The binding proteins remained in higher molecular weight complexes with other substances during molecular sieve chromatography with 1 M acetic acid but eluted at least partially in the expected fractions with 1 M sodium chloride solution. However, further attempts at purification were unsuccessful due to progressive degradation, even though these peptides were relatively stable in ejaculates stored at -18 degC with protease inhibitors. It is suggested that ionic bonds between IGFBP-2 and other components, such as proteoglycans, provide protection from degradation in a similar way as shown for IGFBP-1 and alpha2-macroglobulin.