Uptake of 14C-ascorbic acid by the adrenal and pituitary glands and effect of ACTH or dexamethasone administration

Abstract

The distribution of intravenously administered 14C-ascorbic acid (14C-AA) among various tissues of the rabbit and the dog and the effects of dexamethasone or ACTH administration on the distribution were studied. Two hours after the i.v. dose the concentration of 14C-AA was higher in the adrenal than in any other tissue examined. As a function of time, the difference of 14C-AA concentration between adrenal and surrounding organs became greater and 24 hr after the dose the adrenal: liver ratio became 5:1 in dogs. The concentration of 14C-AA in the pituitary gland gradually increased, reaching a peak at 24 hr and exceeding the adrenal concentration at 48 hr and thereafter. After suppression by dexamethasone the concentration of 14C-AA in the adrenal gland was significantly lower than the control value, although the hormone had no detectable effect on the concentration in other tissues. Injection of ACTH for three days before administration of the 14C-AA produced no significant effect on the accumulation of 14C-AA in the adrenal. A single dose of ACTH given 1 hr prior to the 14C-AA, however, significantly increased the accumulation in the adrenal. These results suggest that accumulation of AA in the adrenal occurs through mechanisms that are more complex than those proposed in the literature. The results also suggest that AA may be an effective pituitary scanning agent if it can be labeled with a suitable radionuclide.