A Comparative Study of Lactogenic Hormone Binding Sites in the Adrenal Gland, Ovary and Kidney of the Lactating Cow

Abstract

The specific binding of ¹²⁵I-oPRL to microsomal fractions from the adrenal gland, ovary and kidney of the lactating cow was significantly lower than binding of iodinated hGH. In addition, the ability of oPRL to compete with iodinated hGH as compared to hGH, was 50-fold lower in the adrenal gland 35-fold lower in the ovary and 18-fold lower in the kidney. These results are similar to those obtained in the mammary gland and liver, whereas the ability of oPRL to compete with iodinated hGH was 90-fold lower, as compared to hGH. In the kidney the difference between the binding of iodinated hGH and iodinated oPRL was smaller. Results obtained with a solubilized kidney microsomal fraction also show a slightly higher affinity for oPRL than in other tissues. Thus the phenomena of differential affinities of oPRL and hGH to lactogenic hormone binding sites, characterizes most lactogenic hormone target tissues in the lactating cow. The distribution of these sites in different parts of the tissues was also studied. In the adrenal gland, the binding capacity in the cortex was 8-fold higher than in the medulla. In the ovary most of the binding sites were found in the corpus luteum, while in the kidney the binding capacity was higher in the cortex as compared to the medulla.