TCDD ALTERS PITUITARY-ADRENAL-FUNCTION .1. ADRENAL RESPONSIVENESS TO EXOGENOUS ACTH

Plasma ACTH concentrations in 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin ( TCDD)-treated rats (50 mug/kg; single, oral dose) were 2.1-, 2.1-, 2.9 -, 1.7-, 1.5-, 2.0- and 3.0-fold greater than control values, respecti vely, at days 1, 3, 5, 7, 10, and 14. At days 1 and 5 plasma corticost erone concentrations were increased 5.1- and 8.0-fold, respectively; w hereas, at days 10 and 14 they were depressed to values of 50% and 39% of controls, respectively. Adrenal glands were exised from rats treat ed with TCDD and corticosterone production was assessed. Basal cortico sterone concentrations produced by treated adrenals were depressed to 81%, 72%, and 71% of control values at days 5, 7, and 14, respectively . Corticosterone secretion by ACTH stimulated adrenals was equivalent to controls. These findings suggest that TCDD exposure decreases the b ioactivity of the ACTH secreted by the anterior pituitary.