Effects of intravenous administration of prostacyclin on regional blood circulation in awake rats

The effects of intravenous infusion of prostacyclin (PGI 2 , 0.1, 0.2, 0.3 and 1.0 μg kg −1 min −1 lasting 5 min) on regional blood flow and regional vascular resistance have been studied in awake rats using the radioactive microsphere method. The control values of blood flow to the heart, kidney, small intestine, hind limb muscle, pericranial skin and brain as well as the corresponding vascular resistance were not modified by an i.v. infusion (0.1 ml min −1 ) of Tris‐buffer (the vehicle of PGI 2 ). The i.v. infusion of PGI 2 produced graded dose‐dependent decreases of MAP (r=0.87, P <0.001; ED 20 =0.73 [0.13–2.55] μg kg −1  min −1 ) as well as decreases of vascular resistance in the heart (r=0.83, P <0.001; ED 30 =0.17 [0.09–0.31] μg kg −1  min −1 ), pericranial skin (r=0.88, P <0.001; ED 30 =0.28 [0.18–0.43] μg kg −1  min −1 ) and small intestine (r=0.74, P <0.001; ED 30 =0.21 [0.11–0.39] μg kg −1  min −1 ), which led to dose‐related increases of blood flow to these territories. On the contrary, PGI 2 increased vascular resistance in skeletal muscle (r=0.73, P <0.001; ED 30 =0.20 [0.10–0.39] μg kg −1  min −1 ) with corresponding reductions in blood flow. The low doses reduced renal blood flow but there were no significant changes during the high ones. Cerebral vessels did not dilate during any infusion of PGI 2 and cerebral blood flow decreased as MAP fell (r=0.56, P <0.01). We conclude that, in awake rats, the coronary vessels are extremely sensitive to the vasodilating effect of PGI 2 and that the mesenteric vessels and those of the pericranial skin are very responsive too. Moreover, autoregulation is inefficient to maintain cerebral blood flow during infusion of PGI 2 .British Journal of Pharmacology (1999) 126 , 1325–1332; doi: 10.1038/sj.bjp.0702426