Effect of pituitary hormones on .ALPHA.-amino-.BETA.-carboxymuconate-.EPSILON.-semialdehyde decarboxylase in rat.

The hormonal regulation of α-amino β-carboxymuconate-ε-semialdehyde decarboxylase (picolinic carboxylase) was studied to clarify the change of tryptophan-niacin metabolism in the different physiological states. Hypophysectomized rats were administered with predonine hemisuccinate and various kinds of pituitary hormones for 2 or 4 days every 12 hr. The activity of their liver picolinic carboxylase was then assayed. The injection of predonine alone elevated the enzyme activity in hypophysectomized rats. On the other hand, rat or bovine pituitary extract was found to suppress such enzyme induction when it was administered prior to predonine injection. The enzyme-suppressing activity of the pituitary extract was lost by heat treatment or addition of proteolytic enzyme such as trypsin and chymotrypsin. These results indicate that the effective substances in the extract may be polypeptides. By gel filtration of bovine pituitary extract, two effective fractions were obtained, which were able to suppress the predonine-dependent induction of liver picolinic carboxylase. The molecular weights of these substances were estimated to be about 23, 000 and 2, 000-4, 000, respectively. Both of these effective substances were shown to be localized in the anterior lobe of hypophysis. In the many kinds of pituitary hormones tested, bovine somatotropin and mammalian prolactin were found to be effective in suppressing the predonine-dependent induction of liver picolinic carbo xylase in hypophysectomized rats. To obtain some information on the mechanism by which liver picolinic carboxylase activity is elevated in diabetic rats, bovine somatotropin or rat pituitary extract was administered to diabetic rats for 4 or 7 days every 12 hr. This hormone treatment was not observed to depress the enzyme activity in the diabetic rats. These results are considred to suggest that changes in pituitary hormone are not responsible for the elevation of the enzyme activity in the diabetic rat.