Macusine B: further pharmacology

Macusine B reduced the induction time and potentiated the barbiturate sleeping time of mice, possibly as a consequence of the hypothermia produced by the alkaloid. There was no evidence to suggest that macusine B affects the synthesis or metabolism of noradrenaline, dopamine, 5-hydroxytryptamine or γ-aminobutyric acid in the rat brain, nor was there any evidence to suggest that it affected the binding of noradrenaline and 5-hydroxytryptamine within the brain. There is an indication that macusine B may act on central adrenergic receptors. The slight depression of the behavioural activity which occurs in rats and mice after the injection of macusine B was probably due to the hypothermia induced by the alkaloid.

An investigation of the pharmacology of macusine B

Macusine B, an alkaloid isolated from Strychnos toxifera, blocks α-adrenergic receptors and stimulates β-receptors in vivo and in vitro. It partially blocks the response of the isolated rabbit heart and the cat blood pressure to tyramine. Macusine B is a competitive inhibitor of 5-hydroxytryptamine on the guinea-pig ileum and also blocks the action of this spasmogen on the rat uterus.