Stimulation of the synthesis of hepatic fatty acid synthesizing enzymes of hypophysectomized rats by 3,5,3'-l-triiodothyronine.

The levels of hepatic fatty acid synthesizing enzymes, acetyl-CoA carboxylase and fatty acid synthetase, are lowered to about one-tenth of the controls in hypophysectomized animals, whereas the lung enzymes decrease by only 25–30%. Administration of 3,5,3′-l-triiodothyronine to the hypophysectomized animals returns the hepatic and lung enzyme activities to the control values. Optimum levels are achieved at a dose of about 150 μg/100 g body wt and 3–4 days after triiodothyronine administration. The triiodothyronine response can be reduced by 80% with actinomycin-D or cycloheximide but not with hydrocortisone hemisuccinate. Antibody-antigen titrations and measurements of the rate of synthesis of fatty acid synthetase are indicative of increased synthesis of fatty acid synthetase and not of activation of the preexisting inactive species. These measurements provide evidence for the involvement of hormones other than insulin in the control of synthesis of fatty acid synthesizing enzymes.