Both Milrinone and Colforsin Daropate Attenuate the Sustained Pial Arteriolar Constriction Seen After Unclamping of an Abdominal Aortic Cross-Clamp in Rabbits

Abstract

We previously reported that unclamping of an abdominal aortic cross-clamp causes initial dilation of pial arteries followed by sustained constriction. Both milrinone and colforsin daropate have a vasodilator action, and both have been used in such critical conditions as abdominal aortic aneurysmectomy. We measured cerebral pial arteriolar diameters using a rabbit closed cranial window preparation before (baseline) and 15 min after the start of an IV infusion of 0.9% saline (control group), milrinone, or colforsin daropate (0.05 and 0.5 microg . /kg(-1) . min(-1)) (pre-clamp), just after aortic clamping, 20 min after clamping, and at 0 to 60 min after unclamping. In the control group, a significant decrease in diameter persisted for at least 60 min after unclamping (maximum, -15% for large and -26% for small arterioles versus baseline). These values were significantly smaller after both doses of milrinone and the larger dose of colforsin daropate (-5% and -8%, 10% and 12%, and -2% and -5%, respectively vs baseline, at 60 min). In a second experiment, changes in regional cerebral blood flow and tissue oxygen tension reflected changes in vascular variables. Thus, sustained cerebral pial arteriolar constriction induced by aortic unclamping can be attenuated by IV milrinone or colforsin daropate.