Discrepancy between Immunoactivity and Bioactivity of Big-big and Big Human Growth Hormones in Acromegaly

Abstract

The heterogeneity of hGH in the sera, culture media of tumor cells and tumor extract from acromegalic patients was studied employing gel chromatography, RIA and lymphoma cell bioassay.
The chromatographic profile of the sera on Sephadex G-100 (superfine) column showed three peaks: the major peak eluted with 125I-hGH (little hGH), the less retarted small peak (big hGH) and the peak at void volum (big-big hGH). Bioassay to radioimmunoassay ratio of big-big, big and little hGH were 1.07-5.75, 0.25-0.70 and 0.70-1.56, respectively. These ratios were not significantly different among the acromegalic sera obtained before and after TRH test.
The longer duration sera were kept for, the higher percent of big-big hGH and the lower percent of little hGH the sera contained by RIA. The percentage of big-big hGH was less in the culture media of tumor cells than that in acromegalic sera, and the least in tumor extract by RIA. Rechromatography of big-big hGH fraction of tumor extract showed the conversion of big-big hGH to big and little hGHs. These data suggest that big-big hGH was artificially made from little and big hGH during storage.
Rechromatography of fractions between big-big hGH and big hGH produced another peak (medium-big hGH) with approximately 80 K-90 K daltons of molecular weight. This peak was converted to almost a little hGH peak after mercaptoethanol treatment and was supposed to be a tetramer of little hGH.