QUANTITATIVE IMAGE-ANALYSIS STUDY OF THE CEREBRAL VASODILATORY ACTIVITY OF NICARDIPINE IN SPONTANEOUSLY HYPERTENSIVE RATS

The effect of the Ca2+ channel blocker nicardipine on the circle of Wi llis and the different sized pial arteries was assessed in 20-week-old spontaneously hypertensive rats (SHR) using quantitative image analys is techniques. Normotensive Wistar Kyoto (WKY) rats were also used as a normotensive reference group. In SHR a significant increase of systo lic blood pressure (SBP) is noticeable in comparison with WKY rats. Th e media-to-lumen ratio was increased in the circle of Willis arteries, large sized (diameter > than 150 mu m), medium sized (diameter betwee n 150 and 50 mu m) and small sized (diameter < than 50 mu m), pial art ery branches. An increase in the thickness of the tunica media and a l uminal narrowing was also seen in medium and small sized pial arteries of SHR in comparison with WKY rats. Treatment with an oral dose of 10 mg/Kg of nicardipine 3 h before the sacrifice significantly reduced S BP in SHR. The drug was without effect on circle of Willis and on larg e sized pial arteries. Moreover, treatment with nicardipine reduced th e thickness of the tunica media, the media-to-lumen ratio and increase d the luminal area in medium and small sized pial artery branches. The se findings show that treatment of SHR with nicardipine significantly reduces SBP and causes a moderate vasodilatation of arteries regulatin g cerebrovascular resistance. This property may be useful in avoiding generalized or exaggerated cerebrovascular dilatation which could be a ccompanied by impaired brain perfusion in hypertension.