In vitro and in vivo inhibition by benserazide of clorgyline-resistant amine oxidases in rat cardiovascular tissues

Abstract

Benserazide ( d, l-serine 2-[2,3,4-trihydroxybenzyl]-hydrazide) has been shown to inhibit the clorgyline-resistant amine oxidase (CRAO) activities which metabolize benzylamine in homogenates of rat aorta, heart and brown adipose tissue. In vitro studies showed a concentration- and timedependent inhibition of CRAO in heart and aorta which was reversed by dialysis for 18hr. At high concentrations (10 −4−10 −3M) benserazide appeared to increase enzyme activity towards and occasionally above control value. These increases became more prominent after long periods of preincubation (especially in the presence of saturating benzylamine concentrations) and remained after dialysis of those homogenates preincubated with benserazide. The administration of benserazide for one or seven days in daily doses of 5–150 mg/kg also inhibited CRAO activity in vivo in a dose-dependent manner, with greater inhibition after seven days treatment. Reversal of inhibition, by dialysis of tissue homogenates from benserazide-treated rats, was much slower than was found with homogenates incubated in vitro with the drug. After benserazide administration to rats, MAO-A activity towards 5-hydroxytryptamine was generally not inhibited, and in fact was significantly increased in some cases. The administration of l-DOPA (250 mg/kg) together with benserazide (40 mg/kg) resulted in a similar degree of CRAO inhibition m aorta and heart to that seen after benserazide alone. These findings are discussed with regard to the use of these drugs in the therapy of Parkinson's Disease, although the paucity of information about the physiological function of CRAO makes the significance of its inhibition by benserazide unclear.