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Hypotensive effects of the intravenous injection of adenine compounds [adenosine triphosphate (ATP), adenosine] were compared with those of sodium nitroprusside (SNP) in rabbits during light, stable halothane anesthesia. ATP and adenosine were almost equipotent in their effects on blood pressure and heart rate. The hypotensive potencies of ATP and adenosine were approximately 1/6 (bolus injection) and 1/40 (continuous infusion) that of SNP, but the adenine compounds had a more rapid onset of action and shorter recovery times than SNP. With bolus injection, SNP invariably caused a baroreceptor-mediated reflex increase in heart rate. In contrast, ATP and adenosine caused a dose-related decrease in heart rate and hypotension. With continuous infusion, ATP and adenosine produced immediate onset of hypotension without tachycardia. Blood pressure remained rematkably stable throughout the infusion; neither tachyphylaxis nor rebound hypertension were observed. Thus, the adenine compounds offer possible advantages over SNP as they are physiologic agents with little or no acute toxicity and may be devoid of tachycardia, tachyphylaxis, and rebound hypertension.