Somatotrophic receptors in hepatic tissue of the developing male pig

The development of hepatic somatotrophic receptors and plasma concentrations of insulin-like growth factor-I (IGF-I) were investigated at five different ages (2, 20, 35, 105 and 165 days) in four male pigs per group. The specific binding of 125I-labelled porcine GH (pGH) to hepatic somatotrophic membranes was very low at 2 days of age (0.53 +/- 0.12%), and increased progressively (P less than 0.01) with advancing age to 3.60 +/- 0.95% at 165 days of age. Specific binding of 125I-labelled bovine GH (bGH) to the same membrane preparations was markedly higher than binding of 125I-labelled pGH; it also showed a distinct developmental increase (P less than 0.01) with age from 4.4 +/- 0.55% at 2 days of age to 24.0 +/- 1.90% at 165 days of age. Plasma concentrations of IGF-I increased significantly (P less than 0.01) from 79 +/- 14.0 micrograms/l at 2 days of age to 610 +/- 64.0 micrograms/l at 165 days of age. Non-linear regression analysis of the competitive binding data using bGH as labelled and unlabelled ligands showed linear Scatchard plots in the three youngest age groups, with an association constant (Ka) of approximately 3.5 litres/nmol. Curvilinear Scatchard plots were observed in the two oldest age groups. The Ka for the higher affinity binding site (approximately 5.0 litres/nmol) was very similar to that for the sole site observed in the younger animals. The Ka of the lower affinity binding site was approximately 0.35 litres/nmol.(ABSTRACT TRUNCATED AT 250 WORDS)