Obese Zucker rats are normotensive on normal and increased sodium intake

The purpose of this study was to determine whether genetically obese Zucker rats have higher arterial pressures than lean littermates on normal and high sodium intakes. Mean arterial pressure was directly measured in chronically instrumented Zucker rats (six lean [weight, 345.8 +/- 8.0 g] and five obese [529.0 +/- 6.2 g]) for 2 weeks on both a normal (2 meq sodium/day) and high (6 meq sodium/day) sodium intake (7 days each). In addition, daily heart rate, water intake, urine output, urinary sodium excretion, urinary potassium excretion, and weekly fasting plasma insulin levels were measured. Obese rats exhibited significantly lower heart rate and greater water intake and urine output compared with lean rats whether maintained on control or high sodium intakes. Urinary sodium excretion, however, was identical in lean and obese rats throughout the experiment. Fasting plasma insulin levels in obese rats were seven times greater than those in lean rats. When the rats were maintained on a 2 meq/day sodium intake, mean arterial pressures obtained from the two groups were similar: 103 +/- 1 versus 106 +/- 1 mm Hg (lean versus obese). An increase in sodium intake did not significantly affect mean arterial pressure in either group: 101 +/- 1 versus 105 +/- 1 mm Hg (lean versus obese). These results indicate that at 12-14 weeks of age, male obese Zucker rats do not exhibit higher resting arterial pressures than lean littermates when maintained on normal or high sodium intake.