Differential effects of isosorbide dinitrate and nitroprusside on pial vessel diameter in cats

: Changes in pial vessel diameter combined with regional cerebral blood flow (CoBF) during infusion of vasodilating drugs, isosorbide dinitrate (ISDN) 5 micrograms/kg/min and nitroprusside (NTP) 5 micrograms/kg/min, compared with haemorrhagic hypotension were studied in cats anesthetized with halothane (1.0%). Pial arteries and veins were measured by image-splitting technique and were each divided into three groups according to the reference diameter: I; < 50 microns, II; 51 < microns < 100, III; 101 < microns. With either drug, the mean blood pressure (mBP) decreased by 10-20%. There was significant decrease in cerebral vascular resistance with ISDN compared with haemorrhagic hypotension while CoBF (H2 clearance) remained unchanged. Dilatation of pial arteries depending on vessel size with ISDN was two-hold compared with haemorrhagic hypotension without any change in all veins. Consistent and significant dilation of veins (I and II) was observed only during NTP infusion. These findings indicate the differential effect of ISDN and NTP on pial arteries and veins.