The effect of 3,3',5-triiodo-L-thyronine on the renal handling of citrate.

Abstract

The effects of a 500 mug injection of T3 on the renal handling of citrate by the albino rat was studied by measuring citrate synthase activity, NADP-isocitrate dehydrogenase activity, and plasma, kidney, and urine citrate concentrations 12, 18, 24, 36, and 48 hr after injection. Kidney citrate synthase activity of the T3-injected rats was significantly lower than the controls in the 24- and 36-hr treatment groups, while NADP-IDH activity was significantly lowered only in the 36-hr treatment group. The injection of T3 resulted in hypercitricemia in the 12-, 18-, and 48-hr experimental animals while there was no significant change in citrate between the control values and treated values in the 24- and 36-hr experiments. There was no significant change in renal citrate levels in any of the treatment groups and hypercitrauria was not observed. The results of the present study suggest that T3 can control citrate utilization by increasing the levels of circulating citrate and then increasing the utilization of citrate by the kidney. This is facilitated by a decrease in NADP-IDH activity resulting in a decrease in biosynthesis and a decrease in citrate synthase activity resulting in a decrease in FFA metabolism. It is proposed that this system functions in providing fuel (citrate) for the increased Krebs cycle flux occurring in hyperthyroidism.