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(Circulation. 1995;91:471-475.)
© 1995 American Heart Association, Inc.

Articles

Sodium Pentobarbital Versus -Chloralose Anesthesia

Experimental Production of Substantially Different Slopes in the Transmural CP/ATP Ratios Within the Left Ventricle of the Canine Myocardium

Dipti P. Rath, PhD; Charles M. Little, DO; Huzeng Zhang, MD; Zongchen Jiang; Amir M. Abduljalil, PhD; Hui Zhu, MD; Xiaoxin Tong, MD; Charles Brown, MD; Robert L. Hamlin, DVM, PhD; Pierre-Marie L. Robitaille, PhD

From the Departments of Radiology (D.P.R., H. Zhang, Z.J., A.M.A., H. Zhu, X.T., P-M.L.R.), Veterinary Physiology (R.L.H.), Emergency Medicine (C.M.L., C.B.), and Medical Biochemistry (P-M.L.R.), The Ohio State University, Columbus.

Correspondence to Pierre-Marie Robitaille, PhD, MRI Facility, 1630 Upham Dr, The Ohio State University Hospitals, Columbus, OH 43210.

Background Transmural analyses of the creatine phosphate (CP)/ATP ratio in various lamina of the canine myocardium have previously revealed significant variations in the CP/ATP ratio, with the subendocardial layer displaying a decreased ratio relative to the subepicardial layer. Without exception, these results were obtained under sodium pentobarbital anesthesia. These findings have been interpreted to imply that the normal endocardium may be operating in the oxygen-limited domain or that there are transmurally varying set points for the regulation of oxidative phosphorylation.

Methods and Results In this work, we examine the effect of the anesthetic regimen on the transmural CP/ATP ratio within the left ventricular wall of the canine myocardium using spatially localized ³¹P-nuclear magnetic resonance (NMR) and an open-chest model. Two anesthetics were compared, -chloralose and sodium pentobarbital. Under sodium pentobarbital, the CP/ATP ratio ranged from 1.92±0.06 to 2.51±0.08 from endocardium to epicardium, resulting in a transmural slope in the CP/ATP ratio of 0.149±0.047 (n=22). Under -chloralose, CP/ATP ratios ranged from 2.18±0.05 to 2.32±0.06, with a transmural slope of 0.035±0.018 (n=38). Thus, the transmural slope in CP/ATP ratio was nearly four times greater with sodium pentobarbital than with -chloralose, and the difference in these slopes was statistically significant (P=.029). No difference was observed in average CP/ATP obtained from the entire wall with either anesthetic.

Conclusions These results demonstrate that the transmural trend in CP/ATP ratio previously reported in the myocardium is likely to be a direct reflection of the sodium pentobarbital anesthetic regimen, not truly reflecting the trend in the normal unanesthetized animal. Moreover, since the transmural variation in CP/ATP ratio was greatly reduced with -chloralose, it appears unlikely that the endocardium in the normal unanesthetized heart is operating in the oxygen-limited domain. These results also point to the importance of the anesthetic regimen in biochemical analysis, indicate the necessity of increased caution in directly translating results obtained under anesthesia, and demonstrate the unique power of in vivo NMR to extract such subtle biochemical information.

Key Words: myocardium • spectroscopy • adenosine

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