Hypertension and Exaggerated Sympatho‐excitatory Reflexes are Reduced by Low Salt Diet in Male Obese Zucker Rats with no Effect in Lean Zucker Rats

Abstract

Adult male obese Zucker rats (OZRs) develop sympathetically‐driven hypertension and exaggerated sympatho‐excitatory reflexes compared to age‐matched male lean Zucker rats (LZRs). Compared to LZRs, male OZRs on a standard rodent diet (0.5–1% NaCl) display attributes seen in salt sensitive rats consuming a high salt diet, such as suppressed plasma renin activity and exaggerated sympatho‐excitatory reflexes. The present study examined whether these attributes would be reduced in male OZRs on a low salt diet (0.1% NaCl). Rats were placed on diets with 0.5–0.85% NaCl (control diet; 10 OZRs and 8 LZRs) or a diet with 0.1% NaCl (low salt diet; 12 OZRs and 10 LZRs) for 14–28 days. After consumption of a low salt diet, baseline mean arterial pressure (MAP) was reduced in urethane‐anesthetized OZRs (125.7±4.4 vs 111.8±4.1 mmHg, P <0.05) but not in LZRs (116.3±4.6 vs. 113.1±5.6 mmHg). Stimulation of sciatic nerve (1 msec pulses for 5 sec at 20 Hz, 100–800 μA) evoked intensity‐dependent increases in MAP and splanchnic sympathetic nerve activity (SNA) in OZRs and LZRs on both diets. Consumption of a low salt diet reduced the sciatic stimulation‐induced rises in SNA in OZRs (800 μA increased SNA 96±7.6% with control diet and 75.3±4.7% with low salt diet, P <0.05) with no effect of diet in LZRs (800 μA increased SNA 87.4±4.4% with control diet and 83.0±8.8% in with low salt diet, n.s.). In contrast, low salt diet reduced the sciatic stimulation‐induced rises in MAP in OZRs and LZRs. These data suggest that consuming a diet containing 0.5–1.0% NaCl contributes to elevated baseline MAP in OZRs and exaggerated sympatho‐excitatory reflexes compared to male LZRs. However, both OZRs and LZRs show reduced sympathetically‐mediated rises in MAP on low salt diet. This study suggests that in male OZRs consumption of a standard rodent diet with 0.5–1.0% NaCl promotes some physiological effects observed in salt‐sensitive strains of rats on a high salt diet.Support or Funding InformationMechanisms for Impaired Short‐Term Control of Blood Pressure with Obesity (R01HL132568, Dr. Ann M. Schreihofer)