APStracts 2:0089H, 1995.

Reduced parasympathetic control of heart rate in obese dogs . Vliet, Bruce N. Van, John E. Hall, H. Leland Mizelle, Jean-Pierre Montani, and Manis J. Smith, Jr. Division of Basic Medical Science, Faculty of Medicine, Memorial University of Newfoundland, Canada, A1B 3V6, Department of Physiology and Biophysics, University of Mississippi Medical Center, Jackson, Mississippi, U.S.A. 39216-4505

APStracts 2:0089H, 1995.

We investigated why resting heart rate is elevated in dogs fed a high saturated fat diet for 12.7 +/- 1.8 weeks. Obese dogs exhibited elevated body weight (59%), blood pressure (14%), and heart rate (25%). Differences in resting heart rate (control: 58 +/- 5 beats x min-1; obese: 83 +/- 7 beats x min-1) were abolished following hexamethonium, indicating an autonomic mechanism. Hexamethonium also reduced blood pressure in obese (20 +/- 4 mmHg) but not control (9 +/- 6 mmHg) animals. Propranolol did not affect heart rate in either group, excluding a [beta]-adrenergic mechanism. Subsequent administration of atropine increased heart rate more in control than in obese dogs (110 +/- 9 vs 57 +/- 11 beats x min-1). The sensitivity of the cardiac limb of the baroreflex (Oxford method) was reduced by 46% in the obese group, confirming impairment of the parasympathetic control of heart rate. The standard deviation of blood pressure measurements was normal when expressed as a percentage of the mean arterial blood pressure (control: 11.2 +/- 0.4%; obese: 11.2 +/- 0.5%). Our results indicate that the development of obesity in dogs fed a high saturated-fat diet is accompanied by an attenuated resting and reflex parasympathetic control of heart rate.

Received 16 August 1994; accepted in final form 27 February 1995.
APS Manuscript Number H738-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 21 March 1995.