Growth hormone and insulin binding to human liver

Specific binding of 125I-hGH to human liver was found in autopsy specimens from 12 to 15 patients. Specific binding was studied using a new technique employing 20 mu thich "microslices" cut on a cryostat. About 0.5 to 1 mg of tissue per assay tube makes feasible the study of small samples. The range of specific binding was 1.4 to 11.7% of 80,000 cpm 125I-hGH added expressed per mg dry weight of tissue. Specific binding was also demonstratable in homogenates and crude membrane preparations from liver. No correlation was seen between 125I-hGH binding and age, sex, or pathology in the series of patients studied. No specific binding of 125I-hGH was observed in lung, adrenal, spleen, or kidney, although all the tissues bound 125I-insulin. Of several species of growth hormone tested, only primate GH displaced 125I-hGH from its binding sites in human liver. No displacement was seen with ovine or human prolactin or with insulin. Primate placental lactogens had only 0.5-1.0% potency of native hGH in displacing 125I-hGH from human liver. Ungulate placental extracts, however, were equipotent with hGH in this respect.