VASOCONSTRICTOR AND CARDIOTONIC ACTIONS OF HALOXYLON-RECURVUM EXTRACT

Intravenous administration of an ethanolic extract of Haloxylon recurv um (30-300 mug/kg) caused a rise in arterial blood pressure in normote nsive anaesthetized rats. Pretreatment of animals with phentolamine (1 mg/kg) abolished the vasoconstrictor response of the plant extract in a way similar to that of norepinephrine (NE). In an isolated rabbit a orta preparation, both plant extract and NE produced contractile respo nses which were blocked by phentolamine (0.3 mug/mL). In isolated guin ea-pig atria, the plant extract caused positive inotropic and chronotr opic responses similar to that of NE and was blocked by propranolol (0 .3 mug/mL). These results suggest that vasoconstrictor and cardiac sti mulatory effects of the plant extract are mediated through mechanisms similar to those of NE (stimulation of alpha-adrenergic receptors in t he blood vessels and cardiac beta-receptors respectively) and hence th is plant contains sympathomimetic constituent(s).