Bn. Vanvliet et al., REDUCED PARASYMPATHETIC CONTROL OF HEART-RATE IN OBESE DOGS, American journal of physiology. Heart and circulatory physiology, 38(2), 1995, pp. 629-637
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%). Differe
nces in resting heart rate (control, 58 +/- 5 beats/min; obese, 83 +/
7 beats/min) were abolished after hexamethonium, indicating an autonom
ic 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 p-adrenergic mechanism
. Subsequent administration of atropine increased heart rate more in c
ontrol than in obese dogs (110 +/- 9 vs. 57 +/- 11 beats/min). The sen
sitivity of the cardiac limb of the baroreflex (Oxford method) was red
uced by 46% in the obese group, confirming impairment of the parasympa
thetic control of heart rate. The standard deviation of blood pressure
measurements was normal when expressed as a percentage of the mean ar
terial blood pressure (control, 11.2 +/- 0.4%; obese, 11.2 +/- 0.5%).
Our results indicate that the development of obesity in dogs fed a hig
h saturated fat diet is accompanied by an attenuated resting and refle
x parasympathetic control of heart rate.