Abstract
Abstract
Previous investigators have reported that specific somatogenic receptors are present in liver membrane preparations from male rats. However, specific binding was less than 3% of total counts per minute added, and the radioreceptor assay using such receptor preparations was impractical to use. Livers from female rats bound 25% of 125I-labeled human growth hormone added, but binding was not specific in that both prolactin and growth hormone competed. Starting with membrane preparations from male rats, we have systematically studied and improved (a) preparation of the fraction, (b) the method of separation of bound and free, (c) time, temperature, and conditions of incubation, (d) the amount of membrane preparation and treatment of rats before sacrifice, and (e) the quality of the labeled growth hormone. As a result, specific binding increased from less than 3 to 60%. This is offered as a model system for optimization of radioreceptor assay systems. The data indicate that 125I-hGH binding to male rat liver membranes was low, as previously reported, because the preparation and assay system had not been optimized, and not because of an inadequate number of receptors in the male liver.
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