Cardiovascular Changes during Sodium Nitroprusside or Adenosine Triphosphate Infusion in the Rat

Abstract

The purpose of these experiments was to compare the cardiovascular and regional hemodynamic effects of two hypotensive drugs, sodium nitroprusside (SNP) and adenosine triphosphate (ATP). Rats anesthetized with halothane were studied under control conditions and during hypotension of 65 and 40 torr induced with intravenous SNP (group 1) or ATP (group 2). Cardiac output and regional hemodynamic changes were measured with radioactive microspheres. A third group of control rats received sham infusions without SNP or ATP. SNP-induced hypotension was associated with no significant changes in heart rate or cardiac output. Hypotension induced with ATP was associated with a significant decrease in heart rate and a significant increase in cardiac output. Cerebral blood flow did not change at mean pressure levels of 65 or 40 torr with either SNP or ATP. Both renal and skin blood flow decreased significantly during SNP- and ATP-induced hypotension. Hypotension induced with SNP and ATP significantly increased skeletal muscle blood flow compared with saline control treatment. These changes were greater in rats treated with SNP than in rats treated with ATP. Differences between SNP and ATP were also observed in myocardial blood flow. Intravenous ATP infusion resulted in 200% to 300% increases in myocardial blood flow whereas SNP produced no significant change. The results indicate that compared with SNP, ATP has certain advantages for the induction of hypotension. These include an absence of tachyphylaxis during hypotensive anesthesia and the ability to maintain a constant level of blood pressure by titrating the ATP dose. Major differences between the two drugs were apparent in skeletal muscle, where SNP was a more potent vasodilator, and in the heart, where ATP was associated with large increases in myocardial blood flow.