Abstract
Summary
A somatomedin bioassay measuring sulfate incorporation into young chick epiphyseal plate cartilage was developed and used to determine somatomedin activity in two animal models. The incubation schedule consisted of 4 hr preincubation and 3 hr incubation. The average index of precision, λ, of the bioassay was 0.18 with increased precision evident in later studies. The sensitivity fell within the range of currently used somatomedin bioassays. Using radioimmunoassay techniques, serum insulin and serum growth hormone levels were measured in lean and obese Zucker rats. Serum from obese Zucker rats was found to have reduced growth hormone levels, reduced somatomedin activity, and elevated insulin levels when compared to their lean littermates. There was no difference in somatomedin activity between slow-growing Ossabaw and fast-growing Yorkshire pigs.
The radioimmunoassay kit for rat growth hormone assay was supplied through the generosity of the Hormone Distribution Office, NIAMD, NIH, Bethesda, Maryland.
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