Studies of Insulin, Growth Hormone and Prolactin Binding: Ontogenesis, Effects of Sex and Pregnancy

Abstract

The ontogenesis of specific binding of 125I-labeled insulin, hGH and oPRL was measured in tissues from rat, rabbit and guinea pig. Binding of 125I-oPRL and 125I-hGH was very low in liver membranes from fetal and immature rats. A 9- fold (oPRL) and 3.5-fold (hGH) increase in binding occurred between 20 and 40 days of age with a greater increase in binding in mid and late pregnancy. Binding to male liver membranes was significantly lower at all stages of development. There were no significant changes in the binding of 125I-hGH from fetal through 30 day rabbit liver membranes. Between 30 and 60 days of age, a 6-fold increase in binding occurred, with a further increase in binding during pregnancy. A similar overall pattern was observed with I25I-bGH. The increase in specific binding of 125I-oPRL was more gradual and occurred earlier than for 125I-GH. In the guinea pig, three patterns of 125I-insulin binding with respect to development were observed. Fetal placenta and kidney showed marked increase in specific binding between earlier (<50 g) and later (>50 g) fetal stages. Binding to liver membranes at both early and late fetal stages remained constant. In contrast, heart membranes from both fetal stages bound 125I-insulin at twice adult levels. Scatchard analysis of displacement curves of rat liver membranes incubated with 125I-oPRL revealed similar affinity constants ranging from 0.7 to 0.9 × 109M−1. However, pregnancy increased binding capacity 3.5-fold. In rabbit liver membranes incubated with 125I-hGH, binding capacity increased 7-fold between 10-day-old rabbit liver membranes and those of 30-day pregnant rabbits. Guinea pig membranes exhibited similar affinity constants ranging from 0.8 to 1.5 × 109M−1. (Endocrinology95: 532, 1974)