Abstract: Aldosterone has been linked to the deleterious cardiovascular effects of obesity in humans.The association of aldosterone with obesity in rodents is less well defined, particularly in models of diet-induced obesity.We hypothesized that adrenal aldosterone production and aldosterone synthase expression would be increased in rats with obesity-induced hypertension.Male Sprague Dawley rats were fed a high-fat (HF: 36 % fat) or control diet from 3 wk of age, and mean arterial pressure (MAP) was measured by telemetry.MAP was increased after 4 wk of HF diet; this was 6 wk before changes in body weight.Mineralocorticoid receptor antagonism did not prevent the HF-induced increase in MAP.After 17 wk on the diets, HF rats had increased body and fat weights (abdominal and epididymal) and were insulin resistant (Homeostasis Model Assessment index: 3.53±0.43vs. 8.52±1.77;control vs. HF, P<0.05).Plasma aldosterone levels were increased in the HF rats (64.14 ± 14.96 vs. 206.25±47.55pg/ml; control vs. HF, P<0.05).This occurred independently of plasma renin activity (4.8±0.92 vs. 4.73±0.66ng/ml/h, control vs. HF).The increase in aldosterone was accompanied by a 2-fold increase in adrenal aldosterone synthase mRNA expression and zona glomerulosa hypertrophy.Rats were also studied after 8 wk of HF diet, a time when MAP, but not body weight, was increased.At this time plasma aldosterone was unchanged but plasma renin activity was increased (4.4±0.5 vs. 8.1±1.3 ng/ml/h; control vs. HF, P<0.05).These studies suggest that rats fed a HF diet from weaning may be a useful model for studying obesity-associated hyperaldosteronism.