EFFECTS OF BIOFLAVONOIDS ON CATECHOLAMINE BIOSYNTHETIC ACTIVITY IN THE ADRENAL-GLAND - INVITRO STUDIES USING PARTIALLY PURIFIED TYROSINE-HYDROXYLASE AND CHROMAFFIN CELL-CULTURES

To elucidate the effects of bioflavonoids on catecholamine biosynthetic activity in the sympathoadrenergic system, the direct actions of bioflavonoids on tyrosine hydroxylase activity were first examined in vitro using the enzyme partially purified from bovine adrenal medulla. The enzyme activity was markedly and rapidly inhibited by quercetin, but not significantly affected by either apigenin or flavone. The inhibitory action of quercetin on tyrosine hydroxylase was shown to be accompanied by an alteration in kinetic properties of the enzyme. Furthermore, the effects of these flavonoid compounds on catecholamine biosynthetic activity were examined using cultured bovine adrenal chromaffin cells, and found that quercetin caused a marked decrease in the formation of [14C]catecholamines from [14C]tyrosine in the cells. In contrast, neither apigenin nor flavone caused any significant effect on the formation of [14C]catecholamines under the same conditions. The findings presented here suggest that quercetin may inhibit catecholamine biosynthesis through its direct action on the rate-limiting enzyme in the adrenal chromaffin cell, thus resulting in modulation of the sympathoadrenergic function. © 1990.