CYTOPLASMIC RECEPTORS FOR GLUCOCOETICOIDS IN INTESTINE OF SUCKLING RATS

Abstract

Previous studies have shown that, in the intact animal, administration of glucocorticoid hormones can precociously simulate the various enzymic and morphological changes that normally occur in the rat intestine at weaning. In order to determine if these hormones act directly on intestinal cells, a search was made for cytoplasmic receptor proteins which are characteristic of target tissues. When incubations were attempted at 4° using ³H-dexamethasone (40 nM) and intestinal cytosol from 18-day-old rats, specific binding was observed but was unstable, being maximal after 1-2 hours then declining rapidly. This problem was overcome by using intestinal rings rather than isolated cytosol; under these conditions it was shown that the specific binding component is saturable and has an apparent dissociation constant of 9.3 ± 2.6 nM and a concentration of 0.24 ± 0.01 pmoles/mg protein in both jejunum and ileum. In a developmental study, the concentration of binding sites was found to decline gradually; from 0.31 ± 0.06 pmoles/mg protein at 5 days to 0.14 ± 0.02 pmoles/mg protein in adults. The presence of these cytoplasmic receptors during the suckling period is taken as evidence that glucocorticoids do act directly on the intestine; but, since there is no dramatic change in their concentration with age, it is unlikely that they play a primary role in the regulation of responsiveness of intestinal tissue to these hormones.

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