HYPERSECRETION OF CORTICOTROPIN-RELEASING HORMONE AND ARGININE-VASOPRESSIN IN HYPOTHYROID MALE RATS AS ESTIMATED WITH PUSH-PULL PERFUSION

The relationship between hypothyroidism and disturbance of the hypotha lamo-hypophysial-adrenal axis was investigated using adult male rats. Hypothyroidism was produced by administration of 4-methyl-2-thiouracil (thiouracil) in the drinking water for 2 weeks. Hypothyroidism decrea sed adrenal weights to 57% of controls and plasma concentrations of co rticosterone to 48% of controls. The changes in the weight of adrenals recovered to control levels by administration of thyroxine. The pitui tary responsiveness to corticotrophin-releasing hormone (CRH) and argi nine vasopressin (AVP) for ACTH release markedly increased in hypothyr oid rats as compared with euthyroid rats. In vivo release of CRH and A VP in median eminence significantly increased in hypothyroid rats as c ompared with euthyroid rats. There were no significant differences in hypothalamic concentrations of CRH and AVP. These results indicate tha t hypothyroidism causes adrenal dysfunction directly and results in hy persecretion of ACTH mediated by increases in synthesis of CRH and AVP in the hypothalamus.