Radioimmunoassay and Radioreceptor Assays for Prolactin and Growth Hormone: A Critical Appraisal

Abstract

The promise and the problems associated with using radioimmunoassays (RIA's) for mammalian prolactins (PRL's) and growth hormones (GH's) for the measurements of these hormones in the blood of foreign species (mammalian and nonmammalian) are considered. When crossreactivity is found with the plasma of a foreign species in heterologously applied RIA's for these hormones of mammalian origin, one can have little confidence about the nature of the crossreacting material that is being measured. Extensive analysis is necessary to establish that a particular RIA system measures the PRL or GH in a foreign species. The question of whether RIA's for PRL and GH give physiologically meaningful measurements of the blood levels of these hormones is considered. In the case of PRL, analysis of our own results and data in the literature raises serious questions about the physiological validity of existing RIA's for mammalian PRL's. Evaluation of the available information on RIA's for mammalian GH discloses that there is no basis for concluding that any of them give measurements of the circulating levels of the hormone that are physiologically meaningful. It is also apparent that the physiological significance of the radioreceptor assays for PRL and GH remains to be established. From analysis of discrepancies between bioassay and RIA estimates of PRL and GH levels in adenohypophysial tissue, incubation medium, and plasma or serum, and of studies on the metabolism of purified and secreted forms of both hormones, it is suggested that the major intraglandular forms of PRL and GH are in fact prohormones.