The Regulation of Growth Hormone Binding Sites in Rat Liver Membranes.

The growth hormone (GH) binding sites of the rat liver were studied by measuring the specific binding of {('125)I}iodo-bGH to liver plasma membranes. There was an age-dependent increase in bGH binding to female rat liver membranes around the age of puberty but not to liver membranes of male rat liver. The specific binding of bGH to membranes of normal male rats was 3 - 4% of the total radioactive hormone added (0.3 - 0.7 ng). Liver membranes prepared from male hypophysectomized rats showed a 2-3 fold increase in specific binding of bGH over age-matched controls. The increase was apparent within 3 days after hypophysectomy and persisted for 3 weeks after the operation. Isolated GH deficiency was produced in normal male rats by intraperitoneal injection of rat GH antiserum (ArGH) produced in a rhesus monkey. Control rats received normal monkey serum. Specific binding of bGH to liver membranes of rats receiving antiserum 1, 3 or 6 h before they were killed was 3-4 fold greater than that to membranes of controls. In contrast, the i.v. administration of bGH (200 ug) to hypophysectomized rats 5-60 min before they were killed almost eliminated specific binding of bGH to the isolated membranes. This decrease may be due to the development of a nondissociable hormone-binding site complex which reduces the number of available binding sites. The changes in bGH binding to the rat liver membranes produced by GH deficiency or acute GH administration appear to correlate with known changes in the sensitivity of the animal to GH under these conditions.Ph.D.Animal PhysiologyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/159051/1/8225011.pd