Glucocorticoid regulation of amino acid and polyamine metabolism in the small intestine.

Several factors (including diets, changes in intestinal fluora, and hormones) regulate postnatal intestinal growth and development. Based on the early studies involving modification of the adrenal gland, pituitary gland or hypothalamus, exogenous glucocorticoids and glucocorticoid receptor antagonists are now used to study glucocorticoid-mediated metabolism of amino acids in the small intestine. Findings from these studies indicate that physiological levels of glucocorticoids stimulate the catabolism of glutamine and proline for the synthesis of citrulline and arginine in enterocytes during weaning. In addition, increases in circulating levels of glucocorticoids enhance expression of arginase, proline oxidase and ornithine decarboxylase, as well as polyamine synthesis from arginine and proline in enterocytes. These actions of the hormones promote intestinal maturation and may have therapeutic effects on intestinal disease (e.g., necrotizing enterocolitis). Molecular aspects, species-specific effects, and developmental responsiveness to glucocorticoids should be taken into consideration in designing both experimental and clinical studies.