Insulin receptors: the binding capacity and localization in the digestive tract during the rabbits neonatal period.

The aim of this study was to localize and measure the receptor-binding capacity for insulin in the stomach, duodenum, ileum, jejunum, caecum, colon and in isolated hepatocytes in 48 rabbits aged 1-7, 14 and 21 days. Two methods were employed: radioimmunoassay (RIA) and receptor-binding assay (RBA). Isolated rabbit hepatocytes were used to estimate the maximal binding (Bo). Insulin (INS) concentrations measured by RIA-INS test were highest in the colostrum (701 microU/mL as 100%) of the does, and in the blood (82 microU/mL) of newborn rabbits during the first day postpartum. The Bo of colostral insulin for isolated hepatocytes was 556 microU/mL, which corresponded to 79.1% of the total binding as assessed by the RIA-INS test. The Bo for insulin binding in the different parts of the digestive tract tested was the highest on the first day (mean 8.0 fM/g) and the lowest on the 6th day postnatally (mean 4.9 fM/g; P < 0.01). The receptor capacity for insulin varied in relation to the different parts of the digestive tract, and with the age of each individual rabbit.