HYPOTENSIVE AND SPASMOLYTIC EFFECTS OF NORMACUSINE-B FROM STRYCHNOS-ATLANTICA ROOT

Normacusine B, a tertiary indole alkaloid, was isolated in pure form f rom the root bark of Strychnos atlantica Krukoff & Barneby. In conscio us unrestrained rats, normacusine B (1 mg/kg) decreased the mean arter ial blood pressure (27.6 +/- 8.4 mmHg, n = 6), followed by a significa nt increase in heart rate (115.0 +/- 12.7 bpm, n = 6). The alkaloid fa iled to induce tachycardia directly in isolated perfused rat heart. In isolated rat aortic rings, normacusine B antagonized phenylephrine an d serotonin-induced contractions. Schild plot analysis of individual c umulative concentration-response curves was compatible with a competit ive type of antagonism against phenylephrine (pA(2) = 7.05 +/- 0.11) a nd of a non-competitive nature against 5-hydroxytryptamine (apparent p A(2) = 7.02 - 0.08). Normacusine B was found inactive against KCl and PGF(2 alpha) induced contractions.