The Effect of 3,3′,5-Triiodo-l-Thyronine on the Renal Handling of Citrate

Abstract

Summary

The effects of a 500-μg 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.