Unimportance of perivascular H+ AND K+ activities for the adjustment of pial arterial diameter during changes of arterial blood pressure in cats

Abstract

The role of perivascular H+ and K+ in the adjustment of pial arterial diameter during changes in arterial blood pressure was investigated in chloralose anesthetized cats. Blood pressure was reduced by i.v. mecamylamine or pentolinium and was increased by i.v. hypertensin. Pial arterioles and arteries with a control diameter ranging from 37--218 microns at a spontaneous mean arterial blood pressure of 128 +/- 16 (SD) mm Hg were studied. Vascular diameter as measured by TV image splitting showed the typical reactions, i.e. constriction during increase (up to 200 mm Hg) and dilation during decrease in blood pressure (down to 60 mm Hg). Perivascular H+ and K+ activities were measured using pH microelectrodes (Hinke type) and K+ ion exchanger microelectrodes, respectively. Under control conditions perivascular pH was 7.25 +/- 0.11 (SD) and K+ activity was 2.46 +/- 0.65 (SD) mM, respectively. During changes in blood pressure the vascular reactions of pial arteries were not accompanied by significant alterations in perivascular H+ or K+ activity. From these data it can be concluded that mechanisms other than those which are mediated by H+ or K+ are involved in the adjustment of pial arterial diameter during changes in arterial blood pressure.