RADIOIMMUNOASSAY STUDIES WITH HUMAN GROWTH HORMONE AND A PITUITARY LIPID MOBILIZING FACTOR

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Abstract
A description is given of a radioimmunoassay procedure for human growth hormone (HGH). Particular emphasis is placed on problems encountered with aggregation and unspecific serum protein binding of the 125I radioiodinated HGH. Immunization of rabbits and guinea pigs with a highly purified lipid mobilizing factor (LMF) from human pituitary glands was attempted. This did not result in antibody formation towards LMF, but gave high titers against HGH. The observation thus suggests that LMF may have structural features in common with the HGH molecule. The antibody towards HGH may, however, also have been produced by a minimal contamination with HGH in the LMF. It was shown that detectable antibody formation towards HGH could be produced in rabbits with as little as 5 [mu]g HGH. During the study of 2 highly purified HGH preparations - the one containing only growth promoting or somatotrophic activity, the other having adipokinetic activity as well - it was shown that the employed radioimmunoassay is specifically directed against the growth promoting part of HGH. Changes in the serum concentration of a possible physiologically acting LMF could therefore not be recorded, neither by a direct assay nor indirectly. On the other hand, the specificity of the HGH assay towards the somato-trophln proper assures that it is indeed this hormone that varies in concentration in response to insulin hypoglycemla, exercise and post-prandlally. The stress of acute cardiac infarction did not increase growth hormone in the blood.