Effects of the spin trap α-phenyl n-tert-butyl nitrone on myocardial function and flow: A dose-response study in the open-chest dog and in the isolated rat heart

Alpha-phenyl N-tert-butyl nitrone (PBN) is widely used in spin-trapping experiments, but its possible toxicity has not been systematically evaluated. The purpose of this study was to investigate the effects of different doses of PBN in cardiac function in vivo (open-chest dogs) and in vitro (isolated rat hearts). In open-chest dogs, PBN was infused intracoronarily to achieve coronary arterial concentrations ranging from 1.6 mM to 10.0 mM. At coronary arterial concentrations of 1.6 mM and 2.5 mM, PBN had no appreciable effect on regional myocardial function (assessed as systolic wall thickening). However, coronary arterial concentrations of PBN of 5.0 mM and 10.0 mM produced a marked reduction and, eventually, a complate loss of systolic wall thickening (53% of baseline values after 30 min at 5.0 mM and 14% after 30 min at 10.0 mM). Furthermore, PBN increased coronary blood flow by ∼ 25% at 2.5 M and by > 100% at 10.0 mM. In isolated rat hearts, perfusion with 2.5 and 5.0 mM PBN for 60 min did not significantly affect global myocardial function, assessed as developed pressure, rate-pressure product, and positive and negative dP/dt. At the 10.0 mM concentration, however, these variables were significantly decreased after 30 min (developed pressure: -77% vs. controls; rate-pressure product: -84%; +dP/dt: -60%; -dP/dt: -70%); two out of five hearts stopped beating within 30 min. Nuclear magnetic resonance spectroscopy with ³¹P showed that 2.5 and 5.0 mM PBN did not significantly affect phosphocreatine (PCr) and adenosine triphosphate (ATP); at the 10.0 mm concentration, however, PCr decreased signficantly (-32% vs. controls after 30 min) and ATP also defined, albeit not significantly. The results of this study demonstrate that PBN is toxic to the myocardium at coronary arterial concentrations of 5.0 mM in the intact dog and 10.0 mM in the isolated rat heart, but can safely used as a spin trap at concentrations of 2.5 mM or less. Furthermore, the data indicate that PBN exerts coronary vasodilator effects in the dog, by as yet unknown mechanism(s).