AUTONOMIC CONTROL OF BLOOD-PRESSURE AND HEART-RATE IN OBESE HYPERTENSIVE DOGS

Autonomic control of cardiovascular function was evaluated in nine dog s before and after a high-fat overfeeding regimen. Body weight increas ed significantly (from 19.8 +/- 0.9 to 29.5 +/- 2.1 kg; P < 0.01) with overfeeding. Mean arterial pressure (MAP) increased from 94.6 +/- 2.1 to 105.5 +/- 3.7 mmHg (P < 0.05), and heart rate (HR) increased from 94.8 +/- 3.5 to 112.3 +/- 5.6 beats/min (P < 0.01). After ganglionic b lockade with chlorisondamine, dose response of MAP and HR to methoxami ne (alpha-agonist) or isoproterenol (beta-agonist) was evaluated. Peak . MAP response to methoxamine was blunted in obese dogs. HR response t o isoproterenol was not different between lean and obese dogs. Atropin e in the presence of propranolol increased HR from 80.8 +/- 7 to 202.8 +/- 8.9 beats/min in lean dogs and from 113.8 +/- 12.1 to 131.7 +/- 1 8.2 in obese dogs. These data suggest the increase in HR observed in o bese dogs may be due to a decrease in parasympathetic inhibition rathe r than an increase in sympathetic stimulation. The blunted response to methoxamine in obese hypertensive dogs suggests that the sympathetic control of peripheral vascular resistance is altered in obesity.