The hypotensive action of Rhazya stricta lyophilized leaf extract was found
to be partly caused by the electrolyte content of the extract, and partly
caused by a strongly basic alkaloidal fraction (AF). AF (0.05-1.6 mg animal
(-1)) caused a dose-dependent reduction in mean arterial blood pressure (MA
P) of urethane-anaesthetized rat preparations. Tn naive pithed rats, AF adm
inistration (0.5-2.0 mg animal(-1)) significantly increased MAP. In pithed
or spinalized rats made normotensive by noradrenaline infusion, AF (0.25 mg
animal(-1)) did not cause any significant changes. Direct intracerebrovent
ricular injection of AF (0.1-0.4 mg) markedly and significantly reduced MAP
. It is suggested that the hypotensive action of AF to be mediated by a cen
tral mechanism. (C) 2000 Academic Press.