Increased growth hormone binding to liver membranes of obese Zucker rats.

Developmental changes in hepatic growth hormone binding sites were examined in the genetically obese male fa/fa rats and in the lean littermates. At 16 days, fa/fa pups are normoinsulinemic; the specific binding of 125I-hGH to liver membranes is comparable in the two genotypes. At 4 weeks and later on, plasma membranes and Golgi fractions of male obese Zucker rats have more GH binding sites than lean littermates. The GH pituitary content is comparable in the two genotypes from 2 to 8 weeks and in 14-week-old fa/fa rats it is half that in lean animals. In the two genotypes plasma IGFI dramatically increases during puberty. At 4 weeks, plasma IGFI level is significantly higher in fa/fa rats than in lean littermates. In this model of genetic obesity, an increased GH binding to liver membranes is observed after the third week of life, shortly after the onset of hyperinsulinemia in the fa/fa rat.