BRAIN CONCENTRATION OF RESERPINE-H3 AND ITS METABOLITES IN THE MOUSE

Effect of low dose intra-arterial reserpine on vascular wall norepinephrine content

A number of reports in recent years have indicated that the administration of low dose intra-arterial reserpine has resulted in significant clinical improvement in patients with symptomatic vasospasm, with the benefits presumably resulting from regional vascular wall norepinephrine depletion with resultant vasodilatation. However, to date, there has been no evidence that such low dose reserpine actually alters vascular wall norepinephrine content. This study was performed to determine both regional and systemic effects of low dose intra-arterial reserpine on vascular-wall norepinephrine content, and the duration of any alterations. Twenty-four mongrel dogs had vascular segments excised and assayed for norepinephrine content, before and for up to 4 weeks following a single injection of reserpine, 0.01 mgm/kg, into one femoral artery. The results indicate a pronounced norepinephrine depletion in the injected femoral arterial system, with the reduction persisting for 2-4 weeks, at which time complete norepinephrine recovery occurred. The visceral vessels sampled also showed considerable norepinephrine depletion, indicating systemic spill-over of the drug from the injected peripheral arterial tree. The visceral vessels, however, showed maximal depletion at 24 hours, with recovery by 7 days.

The relation between the subcellular distribution of [3H]resperpine and its proposed site of action

The amount of [3H]reserpine retained after injection is greater in the heart, a tissue with a high density of adrenergic innervation than in femoral muscle. Subcellular distribution studies emphasized that 15 and 60 min after injection of [3H]reserpine it could not be shown to be uniquely associated with the noradrenaline-containing granules. The possibility existed that the large amount of reserpine bound to cellular lipids at these times might mask a more specific binding. A reduction in the dose and a lengthening of the time between drug administration and tissue measurement to 18 h revealed a small amount of [3H]reserpine to be bound more firmly to the microsomal or amine granule-containing fraction. Prior saturation of tissue binding sites by treatment with large amounts of unlabelled reserpine or tetrabenazine decreased the retention of subsequently injected [3H]reserpine. This decreased tissue retention resulted in an increase in the formation of [3H]trimethoxybenzoic acid.

A model is proposed relating tissue distribution and binding to reserpine's mechanism of action.