Renal clearances and plasma antidiuretic hormone (ADH), 17-hydroxycorticoids, and norepinephrine were measured in unrestrained dogs before and during exposure to ambient cold (minus 4 to + 4 degrees C). Some dogs were treated with an inhibitor of cortisol biosynthesis, Metopirone, either alone or combined with dexamethasone, a potent glucocorticoid suppressing ACTH release. Plasma ADH increased in the Metopirone-treated group (P smaller than 0.02) but changed little in other dogs. Plasma 17-hydroxycorticoids in untreated dogs rose from a control value of 14.4 plus or minus 1.9 (SE) to 1.82 plus or minus 1.2 mug/100 ml after 20 min of exposure (P smaller than 0.01), an increase comparable with that previously observed in restrained dogs. Plasma norepinephrine increased from 0.98 plus or minus 0.07 to 1.15 plus or minus 0.08 mug/liter (P smaller than 0.01) after 20 min of exposure. Urine flow, C-Cr, and C-PAH tended to increase spontaneously in nonexposed control dogs. Exposure to cold abolished or reversed this tendency, most distinctly in the Metopirone-dexamethasone group. The urine concentration, measured as T-c-H2O/C-Cr, did not change in cold, in contrast to a decrease previously observed in restrained dogs. The data do not support the key role of plasma cortisol elevation in the mechanism of urine-concentration defect in cold and demonstrate important differences between responses of restrained and unrestrained animals.
- Copyright © 1975 by American Physiological Society