Development and significance of an in vivo radioreceptor assay for polypeptide hormones

The assay is based on advances in in vivo kinetic studies, radioautographic studies, in vitro receptor assays and previous in vivo binding studies. These were combined with a new tissue compartment distribution theory which is developed and discussed in the dissertation. The assay involves the infusion of both 125I-insulin and 131I-albumin into rats with or without varying concentrations of unlabeled pork insulin. Changes in the plasma concentration of tracers were followed and a computer was used to fit a combination of curves through the experimental data. After various periods of time the animals were sacrificed, tissue samples excised, weighed, and the radioactivity of each isotope assessed. The relative abundance of each tracer in the various tissue samples and blood was then assessed with respect to the distribution theory and the kinetic analysis of the plasma tracer curve by computer. By comparing the result from animals given a very large amount of unlabeled hormone with animals given smaller amounts, the specific binding of insulin to its receptor in a variety of tissues was demonstrated. These include liver, pancreas, spleen, kidneys, submandibular glands, adrenal glands, the digestive tract from stomach to colon, testis, epididymis, seminal vesicles, prostate, fat and muscle. This in vivo radioreceptor assay has extended the overall understanding of hormone-receptor interaction of insulin and is applicable to the study of other polypeptide hormones. It will enable the determination of receptor number, regulation and distribution throughout the body