Blunted natriuretic response to an acute sodium load in obese hypertensive dogs

Several studies support the premise that there is a strong relation between obesity and high blood pressure. Although the mechanism for obesity-related hypertension has not yet been fully elucidated, recent studies have suggested that abnormalities in renal sodium handling may be involved in the pathogenesis of obesity-induced hypertension. The purpose of the present study was to determine the effects of an acute saline load on renal excretory function in dogs with obesity-induced hypertension and in normotensive lean dogs. Experiments were performed in two groups of conscious, chronically instrumented dogs. One group of dogs (obese) was fed a high-fat diet for 5-6 weeks, and the other group (lean) ate a normal diet. The body weight of the obese dog group (26.3 +/- 0.7 kg) was 45% higher than the lean dog group (18.1 +/- 0.3 kg). Mean arterial pressure averaged 126 +/- 2 mm Hg in the obese dogs and 100 +/- 1 mm Hg in the lean dogs. The lean dogs had an average heart rate of 104 +/- 7 beats per minute, whereas the obese dogs averaged 134 +/- 8 beats per minute. Plasma renin activity was also significantly higher in the obese dogs. Both groups of dogs were given 135 meq sodium chloride over 60 minutes via an intravenous infusion of isotonic saline. Sodium and water excretion increased significantly in response to the acute saline load. However, the natriuresis and diuresis was markedly attenuated in the obese hypertensive dogs. During the first 40 minutes of saline loading, the increase in sodium and water excretion was 50-70% lower in the obese hypertensive dogs. The results of the present study indicate that obese hypertensive dogs have a reduced capability to excrete an acute sodium load. This abnormality in renal sodium handling may play a role in the pathogenesis of obesity-induced hypertension.