ADENOSINE-TRIPHOSPHATE CAUSES VASOSPASM OF THE RAT FEMORAL-ARTERY

OBJECTIVE: Adenosine 5'-triphosphate (ATP) causes vasoconstriction by activation of P-2-purinoceptors on vascular smooth muscle cells. Eryth rocytes contain ATP at a concentration (1.6 mmol/L) that contracts smo oth muscle. Previous studies of hemoglobin solutions did not assess wh ether the vasoactivity was caused by ATP rather than or in addition to hemoglobin. It was hypothesized that the hemolysis of erythrocytes th at occurs after subarachnoid hemorrhage releases ATP in concentrations that cause vasospasm. METHODS: Thirty-eight rats were randomly assign ed to undergo placement of one of the following compounds in a silasti c elastomer cuff around each femoral artery: 1) agarose gel (n = 8); 2 ) dog erythrocyte hemolysate (n = 8); 3) purified human hemoglobin (He molink; Hemosol, Inc., Toronto, Canada; n = 8); 4) ATP (n = 8); or 5) clotted autologous blood (n = 6). The amounts of hemoglobins and adeni ne nucleotides in the compounds were measured by spectrophotometry and high pressure liquid chromatography. Hemolysate, purified hemoglobin, and ATP were mixed with agarose gel to create an artificial dot. Rats were killed and fixed by perfusion at physiological blood pressure 7 days after perivascular cuff and spasmogen placement. Vasospasm was as sessed by image analysis of cross sections of fixed femoral arteries. Arteries were assessed for histopathological changes on 3-point scales . RESULTS: There was significant variance in arterial diameters among groups (mean diameter +/- standard deviation: agarose gel, 0.29 +/- 0. 06; purified hemoglobin, 0.28 +/- 0.04; hemolysate, 0.24 +/- 0.05; ATP , 0.25 +/- 0.05; clotted blood, 0.24 +/- 0.01; P < 0.05, analysis of v ariance, n = 11-20). Animals exposed to clotted blood, hemolysate that contained ATP, or ATP, developed vasospasm, whereas purified hemoglob in and agarose did not cause vasospasm. Endothelial proliferation and perivascular inflammation were more severe (P < 0.05) in arteries expo sed to clotted blood, purified hemoglobin, and hemolysate. CONCLUSION: These results suggest that ATP may be a vasospastic substance release d by erythrocyte hemolysis. The concentration of ATP in impure solutio ns of hemoglobin is too low to account for the vasoactivity of these s olutions. The discrepancy between arterial narrowing and histopatholog ical changes suggests that either histopathological changes may not be an important correlate of arterial vasospasm or that other substances are important in vasospasm.