ANTIHYPERTENSIVE ACTION OF GERANIIN IN RATS

The effects of geraniin, one of the ellagitannins purified from the le aves of Sapium sebiferum, on blood pressure were investigated in the s pontaneously hypertensive rat (SHR). A single intravenous bolus inject ion of geraniin into anaesthetized SHRs lowered the arterial mean bloo d pressure in a dose-dependent manner without affecting the heart rate . A similar action was also observed in the normotensive (WKY) rat tha t received this compound at a higher dose. Geraniin did not modify the baroflex sensitivity in the phenylephrine-challenged SHR. This tannin reduced the plasma noradrenaline in a dose-dependent fashion which wa s not influenced by adrenalectomy. Failure of the antagonists, idazoxa n and yohimbine for alpha(2)-adrenoceptors as well as haloperidol and domperidone for dopamine receptors, to reverse the antihypertensive ac tions of geraniin ruled out the possible mediation of these receptors. Moreover, geraniin attenuated the presser responses to exogenous nora drenaline and Bay K 8644 to a similar degree, indicating the direct ef fect of this compound on vascular activity in rats. These results sugg est that geraniin possesses the ability to lower systemic blood pressu re through the reduction of noradrenaline release or by direct vasorel axation.