Experimental Cardiac Hypertrophy

The e f i e c t of experimental cardiac hypertrophy on the e n z y m e s of the m a l a t e a s p a r t a t e shutt le aspar ta te a m i n o t r a n s f e r a s e (AAT) and m a l a t e dehydrogenase (MDH) was studied. ( l ) Aortic constrict ion in adult rats resulted in 25% cardiac hypertrophy in 2 89 weeks. Total DNA (mg per hear t ) did not change. (2 ) The proportions of mitochondrial and cytosolic isozymes of AAT and MDH did not change as a result of cardiac h y p e r t r o p h y . About t w o t h i r d s of each e n z y m e occurred in the mitochondrial form and one-third in the cytosolic form. (3 ) Total AAT in hypertrophic hearts, in e n z y m e uni ts per mg DNA, increased by 24% c o m p a r e d to AAT c o n t e n t in the hearts of shamo p e r a t e d a n i m a l s . To ta l MDH did not change . SoIubilized protein increased by 20%. Normal hearts contained 10 times more enzyme units of MDH than of AAT. (t~) C a r d i a c g rowth s t imu la t ion induced in newborn ra t s did not result in specific changes of e i t h e r e n z y m e . It is sugges ted that true cardiac hypertrophy acts as a specific stimulus for the possibly ratel imit ing enzyme AAT of the shuttle.