Characterization of Somatogenic and Lactogenic Binding Sites in Isolated Rat Hepatocytes

Publisher Website
Google Scholar
Abstract
Suspensions of rat hepatocytes isolated enzymatically by the method of Berry and Friend were used to study the binding of 125I-labeled human (hGH) and bovine (bGH) growth hormones and ovine prolactin (oPRL). Displacement of these labeled hormones by their unlabeled analogs was analyzed by Scatchard plots and affinity constants (K), and the number of binding sites per cell (q) were calculated. Specificity of binding was studied using hGH, bGH oPRL and rat growth hormone (rGH) and rat prolactin (rPRL). Rat hepatocytes contained 2 types of binding sites which bound hGH. The 1st, somatogenic, was specific for the growth-promoting hormones bGH and rGH. The 2nd, lactogenic, was specific for lactogenic hormones, oPRL and rPRL. hGH, which has lactogenic and growth-promoting properties in rodents, bound to both sites. The somatogenic binding sites were present in males and females, and the number of sites was similar in females and males and was not affected by hypophysectomy. The lactogenic binding sites were present only in females, and the number of lactogenic and somatogenic sites was similar (40,000/cell). The affinity of hGH for the lactogenic binding sites was less than for the somatogenic (0.37 .times. 109 vs. 1 .times. 109 M-1). The lactogenic binding sites were lost when female rats were hypophysectomized and could not be restored by estrogen treatment.