Differential regulation of malate dehydrogenase isoenzymes by estradiol in the brain of rats of various ages.

The activity and induction patterns of the isoenzymes of malate dehydrogenase (MDH) of the cerebral hemispheres and cerebellum of female rats during growth, development, and senescence were studied. The activity of both the cytoplasmic and mitochondrial isoenzymes increased significantly with increasing age of the rat. Ovariectomy decreased, and hydrocortisone administration increased significantly the activity of cytoplasmic MDH of both the tissues of immature, adult, and senescent rats. However, the degree of these responses decreased with increasing age of the animal. The hormone-mediated induction of this isoenzyme is actinomycin D-sensitive. Mitochondrial MDH on the other hand is irresponsive towards these treatments throughout the life span of the rat.