[Effects of prostacyclin (PGI2) on pial vessel diameter and carbon-dioxide reactivity in cats]

We studied the effects of prostacyclin (PGI2) on the pial vessel diameter (D) and CO2 reactivity in cats. Nineteen cats, weighing 1.6-4.0 kg, were divided into two groups; PGI2 administration group (n = 10) and the control group (n = 9). The animals were anesthetized with midazolam, fentanyl, pancuronium and nitrous oxide/oxygen and ventilated mechanically. The pial vessels diameter (D) was classified into 4 groups (D < 50 microns, 50 < or = D < 100 microns, 100 < or = D < 200 microns, D > 200 microns). The vascular dynamics was examined through the closed cranial window with intravital epifluorescence microscopy on which a video camera was mounted. The measurements were carried out under the steady state of hypo-, normo-, and hypercarbia, respectively and the CO2 reactivity (delta %D/delta CO) was calculated. Under the induced hypotension with PGI2 (30% reduction in mean arterial pressure), pial vessels were significantly dilated, but there was no change in CO2 reactivity in terms of vessels diameter. The vessels with diameters of less than 50 microns were more dilated compared with those with larger diameters. We concluded that pial arterioles were dilated with PGI2 but it had no effects on CO2 reactivity.