Hypertension in young, healthy Zucker obese rats is not responsive to reduced salt intake

Hypertension in insulin resistant states is, in part, salt and volume dependent. The Zucker obese rat, a model of hypertension associated with insulin resistance, has been shown to exhibit a pressor response to a fourfold increase in NaCl intake, from 1 to 4 g/100 g. However, it is not clear if blood pressure is responsive to less severe manipulations, or if a NaCl restricted diet results in a depressor effect comparable to the pressor effect of adding supplementary NaCl to a normal diet. Consequently, we have determined the effects of NaCl restriction on blood pressure in Zucker lean and obese rats. Twenty-four 6-wk-old female Zucker lean and obese rats were randomly assigned to either a normal diet (1 g/100 g NaCl) or a NaCl restricted (0.26 g/100 g) diet for 4 wk. Direct intra-arterial blood pressure was then measured in conscious, unrestrained animals via a femoral cannula connected to a low volume pressure transducer and physiological recorder. Animals fed both diets grew normally, and there was no effect of diet on either food consumption or growth rate. Blood pressure was significantly higher in the obese than the lean rats. However, reducing NaCl intake had no effect on blood pressure in either group. Heart rate was not significantly different among the 4 groups. These data demonstrate that moderate reductions in dietary NaCl intake are without effect on blood pressure in Zucker obese rats despite their pressor response to large quantities of NaCl.