The new world primates as animal models of glucocorticoid resistance

Many New World primate species have greatly increased plasma cortisol concentrations, decreased plasma cortisol binding globulin capacity and affinity, marked resistance of the hypothalamic-pituitary-adrenal axis to suppression by dexamethasone, and no biological evidence of glucocorticoid excess. These primates also have high levels of circulating progesterone, estrogen, mineralocorticoid, androgen and vitamin D. The glucocorticoid target tissues that have been examined (circulating mononuclear lymphocytes and cultured skin fibroblasts) have normal concentrations of glucocorticoid receptors with decreased affinity for dexamethasone. Transformation of B-lymphocytes with the Epstein-Barr virus leads to glucocorticoid receptor induction that is less than that observed with cells from Old World primates. The receptor in these cells has a low affinity for dexamethasone. The low affinity leads to an increased loss of specific bound ligand during thermal activation. Meroreceptor generation is normal. The molecular weight of the receptor, determined by SDS-PAGE, is similar to that of Old World primates (approximately 92,000) and the activation pattern per se, examined in vitro by heating cytosol and performing phosphocellulose chromatography, appears similar to that of human controls. The ratios of nuclear to cytosolic hormone-receptor-complexes and of cytosolic activated to unactivated receptor complexes in intact cells are similar to Old World primates. Results from mixing studies do not support the hypothesis that a binding inhibitor(s) or a deficient cytosolic positive modifier(s) of binding underlies the findings in these primates. The New World primates, unlike men with the syndrome of primary cortisol resistance, have compensated for their condition with intra-adrenal and mineralocorticoid receptor adaptations. Thus, unlike Old World primates, cortisol in New World primates has only weak sodium-retaining potency because the aldosterone receptor has a low affinity for cortisol. The common element that would explain the apparent resistance to six steroid hormones in New World primates remains unknown.