Heat-labile prolactin immunoreactivity in normal human tissues: artifacts of peptide hormone radioimmunoassay in human tissues

Abstract

We recently demonstrated that a substantial proportion of the previously reported wide spread distribution of human chorionic gonadotropin-like material in nonplacental nor mal human tissues is d ue to non-specific activity of tissue proteases (Adcjuwo n & Segal, 1984). The study was extended to another polypetide hormone, measured by the same general method of radioimmunoassay. Normal tissue samples of colon (/i = 1) and testes (// = 5) obtained at surgery were analysed by a highly specific and sensitive radioimmunoassay (RIA ) for human prolactin (hPRL). All tissues investi gated appeared to contain immunorcactivc hPRL-likc material (6.7 ± 5 . 3 ng/g weight, mean ± s.d.) Heat at 55°C lor 15-20 min was found to have no effect on the immunoreactivity of purified liPRL. Exposure of normal tissues to these conditions was. however , found to completely eliminate the hPR L-like immunoreactivity. T h e factor present in these normal tissues giving positive radioimmunoassay results for hPRL is not identical to native hPRL. It may he due to tissue proteases interfering with the radioligand assay. True polypeptide hormone immunoreactivity must be distinguished from proteolytic activity by treatment with heat or protease inhibitor