Reduced parasympathetic control of heart rate in obese dogs.
We investigated why resting heart rate is elevated in dogs fed a high saturated fat diet for 12.7 +/- 1.8 wk. Obese dogs exhibited elevated body weight (59%), blood pressure (14%), and heart rate (25%). Differences in resting heart rate (control, 58 +/- 5 beats/min; obese, 83 +/- 7 beats/min) were abolished after 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/min). 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.
Van Vliet
B N
BN
Division of Basic Medical Science, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Canada.
Hall
J E
JE
Mizelle
H L
HL
Montani
J P
JP
Smith
M J
MJ
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D017704:Baroreflex / Q000502:physiology; D002319:Cardiovascular System / Q000187:drug effects; D004285:Dogs; D006339:Heart Rate / Q000502:physiology*; D006439:Hemodynamics; D018738:Hexamethonium / Q000494:pharmacology; D009765:Obesity / Q000503:physiopathology*; D010275:Parasympathetic Nervous System / Q000503:physiopathology*; D011433:Propranolol / Q000494:pharmacology; D012146:Rest
D018738:Hexamethonium; D001285:Atropine; D011433:Propranolol