Reaction of pial arteries and veins to hypercapnia in hypertensive and normotensive rats.

The lumen diameters of the main cortical surface arteries were continuously monitored through a closed cranial window in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY). The arterial diameter was significantly smaller in SHR (55 +/- 1 micron) than in WKY (87 +/- 1 micron) during resting conditions as well as during hypercapnic dilatation (87 +/- 2 micron compared to 117 +/- 5 micron). The per cent increase in diameter induced by hypercapnia was larger in SHR (54%) than in WKY (36%), presumably a consequence of the altered vascular wall to lumen ratio. Alpha-adrenoreceptor blockade with yohimbine and phenoxybenzamine had no significant effect on arterial diameter during hypercapnia. The diameters of the largest pial surface veins increased to the same extent in SHR and WKY during hypercapnia (about 10%).