DELINEATION OF AN INSULIN-SENSITIVE-PERIOD DURING RAT SMALL INTESTINAL GROWTH

Abstract

In suckling pups treated with exogenous insulin (IN:12.5 mU.g.b.wt), twice daily, from day 8 to 12, sucrase-isomaltase (SI) measured in BBM was precociously induced while maltase, aminopeptidase and neutral lactase were markedly enhanced (+30 to +131%, p < 0.01 vs controls). N-acetyl-β-glucosaminidase (lysosomes), sulfatase C (microsomes) and lactate dehydrogenase (cytosol) were also sensitive to IN with decreases in villus and crypt cells ranging from -37 to -63% (p < 0.05 vs controls). Whatever the dose of IN given, the production of plasma corticosterone remained similar to saline controls. In weaned rats (d. 23 to 32), IN (12.5 mU) failed to influence the activity of BBM, lysosomal, microsomal and cytosolic enzymes. The synthesis rate of mature S-I, measured by the incorporation of ¹⁴C-leucine into S-I precursor was equivalent in IN-treated rats (0.039 ± 0.006) and controls (0.034 ± 0.005 ratio cpm ¹⁴C-SI/cpm¹⁴C BBM prot.).

In conclusion : (1) the immature enterocyte of the rat is responsive to IN throughout the nursing period while at weaning, the mature enterocyte lost IN responsiveness (2) the effect of IN on the enterocyte is not mediated by endogenous corticosterone release.

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