Isoproterenol-induced maximal heart rate in normothermic and hyperthermic horses

Thomas E. Goetz From the Department of Veterinary Clinical Medicine (Goetz) and Veterinary Biosciences (Manohar), College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, IL 61801.

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Murli Manohar From the Department of Veterinary Clinical Medicine (Goetz) and Veterinary Biosciences (Manohar), College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, IL 61801.

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 BVSc, PhD

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Summary

The heart rate (hr) induced by maximal β-adrenergic activation, which was elicited by infusion of isoproterenol, was studied in 8 healthy horses before (control) and after hyperthermia was induced by iv administration of 2,4-dinitrophenol (dnp). Isoproterenol was administered iv at 1.0 μg·kg-1·min-1 for 3 minutes, and the hr was determined during the final 30 seconds of the infusion. As the rectal temperature increased (P < 0.001) from 38.2 ± 0.1 C (mean ± SEM; normothermic control) to 40.1 ± 0.1 C at 60 minutes after dnp administration, the isoproterenol-induced hr also increased from 198 ± 4 beats/min (control) to 214 ± 4 beats/min (P < 0.001). It appeared that the values of hr achieved with maximal β-adrenergic activation were augmented by the hypermetabolic, hyperthermic state induced by dnp.

Summary

The heart rate (hr) induced by maximal β-adrenergic activation, which was elicited by infusion of isoproterenol, was studied in 8 healthy horses before (control) and after hyperthermia was induced by iv administration of 2,4-dinitrophenol (dnp). Isoproterenol was administered iv at 1.0 μg·kg-1·min-1 for 3 minutes, and the hr was determined during the final 30 seconds of the infusion. As the rectal temperature increased (P < 0.001) from 38.2 ± 0.1 C (mean ± SEM; normothermic control) to 40.1 ± 0.1 C at 60 minutes after dnp administration, the isoproterenol-induced hr also increased from 198 ± 4 beats/min (control) to 214 ± 4 beats/min (P < 0.001). It appeared that the values of hr achieved with maximal β-adrenergic activation were augmented by the hypermetabolic, hyperthermic state induced by dnp.

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