Pial arterial and venous reaction to intravenous infusion of nimodipine in cats.

The calcium-antagonist nimodipine was infused intravenously in ten cats using dosage rates of 0.5 to 3 micrograms kg-1 min-1. The reactions of pial arterial and venous vessels as well as mean arterial blood pressure (MAP) were studied. For analysis of pial vascular reactions, diameter variations were continuously monitored on 50 arterial and 22 venous portions using a multichannel videoangiometer. At 0.5 micrograms kg-1 min-1, pial arteries with a mean resting diameter of 81 microns dilated by 4% (p less than 0.0005); venous diameters decreased by 0.5% (n.s.); MAP declined by 2% (n.s.). At 1 microgram kg-1 min-1, arteries dilated by 25% (p less than 0.0005), venous diameters were diminished by 3.8% (n.s.), MAP decreased by 9% (n.s.). Further significant dilatation of pial arteries was observed at 2 and 3 micrograms kg-1 min-1, however, together with a significant fall of MAP. Arterial vessels smaller than 60 micrograms resting diameter dilated more than arteries above 60 micrograms. After the infusion was stopped, arterial dilatation by some 20% persisted for at least 20 minutes, even when MAP values returned to the resting level.