Effects of nifedipine of pial arteriolar calibre: an in vivo study.

In cats the response of individual pial arterioles to perivascular microapplication of the Ca++-antagonistic drug nifedipine was studied using the image-splitting technique developed by Baez. It has previously been shown that the coefficient of variation for repeated measurements of pial vessel diameter using this system is 1%, under conditions of steady arterial pressure and blood gas tensions. All investigated pial arterioles invariably responded with a dilatation at an injected nifedipine concentration of 10 microM. The dilatatory response was inversely proportional to the resting vessel calibre, i.e., arterioles less tham 70 microns responded with a significantly stronger dilatation as compared with arterioles greater than 100 microns in diameter. In experiments where a minor subarachnoid hemorrhage was made by the injection micropipette injuring capillaries just before the perivascular microapplication of nifedipine, a dilatatory response invariably ensued in spite of the perivascular blood which in itself constricted the arterioles under examination.