Role of the Liver in Regulating Somatomedin Activity: Hormonal Effects on the Synthesis and Release of Insulin-Like Growth Factor and Its Carrier Protein by the Isolated Perfused Rat Liver*

Abstract

Previous studies have indicated that one or more GH-dependen t somatomedins (SMs) are either synthesized or at least released by the liver. Employing the isolated rat liver perfusion technique and a competitive protein-binding assay to measure one of the SMs [insulin-like growth factor (IGF)] and its carrier protein (CP), the net cumulative release of these peptides from normal and hypophysectomized (hypox) rat livers has been studied. The IGF concentration in the perfusates of seven normal livers increased rapidly during the initial 2 h and more gradually during the remainder of a 12-h perfusion. The mean (± SEM) net cumulative release of IGF at 12 h was 5620 ± 740 μU/300 cm2 (donor body surface area). In contrast to the pattern of IGF release, the release of CP was very slow initially but increased rapidly by the 12th h to 5.0 ± 0.9 mg/300 cm2. The addition of bovine GH to the perfusions of six normal livers caused a significant increase in the release of IGF(9210 ± 850 μU/300 cm2) but not of CP (5.4 ± ...