EFFECT OF EXTRACT OF RHAZYA-STRICTA, A TRADITIONAL MEDICINAL PLANT, ON RAT-BRAIN TRIBULIN

Rhazya stricta leaves, which have both antidepressant and sedative pro perties in animal models, are widely used in folk medicine in the Arab ian peninsula. In this study, the effects of oral administration of le af extracts on rat brain tribulin levels [endogenous monoamine oxidase (MAO) A and B inhibitory activity], were determined. In an acute stud y, low doses brought about an increase in MAO A inhibitory activity, w hile intermediate doses caused a significant reduction. The highest do ses had no significant effects on activity-There were no significant e ffects on MAO B inhibitory activity at any dose. Subchronic administra tion (21 days) caused a significant decrease in MAO A inhibitory activ ity, most prominent at low dosage, and an increase in MAO B inhibitory activity. Acute intramuscular administration also resulted in a simil ar pattern. Such paradoxical effects were at least partially explained when different extracts of the leaves were used; a weakly basic chlor oform fraction caused an increase in MAO A inhibitory activity, wherea s butanol extracts brought about a decrease. These fractions had no si gnificant effects on MAO B inhibitory activity. The findings show that Rhazya stricta leaves contain at least two different components that affect MAO inhibitory activity in opposite directions. It may be that the antidepressant and sedative actions of the plant are explicable in terms of these different components. (C) 1998 Elsevier Science Inc.