Abstract
The activity of lactate dehydrogenase (LDH, E. C. 1. 1.1. 27) is relatively high in the anterior pituitary and all five forms of LDH isoenzymes are demonstrated. The relative proportion of M-containing isozymes is about 80% in the normal controlgroup. Both relative and absolute amounts of M type were increased following thyroidectomy and decreased by L-thyroxine (T4) supplement. Some changes in kinetic properties of the anterior pituitary LDH were observed under these altered circumstances. The production of lactate by the rat anterior pituitary was decreased after thyroidectomy, the most decreased formation of lactate being observed 5 days after operation. The decreased lactate formation was restored to the normal level 72 hrs. after T4 treatment. It has been shown that the rate of lactate formation by the anterior pituitary is not dependent on total LDH activity, nor correlate with the change in the isozyme pattern. The incompatibility between the alteration of the LDH isozyme pattern and that of the pituitary carbohydrate metabolism in various thyroid states is discussed.
