Hypertension in insulin-resistant Zucker obese rats is independent of sympathetic neural support

We have previously reported that insulin-resistant Zucker obese rats exhibit hypertension associated with impaired vascular smooth muscle (VSM) Ca2+ transport and proposed that this results from failure of insulin to regulate VSM Ca2+ transport in insulin resistance. However, hypertension in insulin-resistant states is generally attributed to hyperinsulinemia, with a consequent stimulation of sympathetic neural activity. Accordingly, the present study was conducted to determine whether the hypertension observed in Zucker obese rats compared with their lean controls was dependent on either increased sympathetic neural activity or exaggerated vascular reactivity. Intra-arterial blood pressure responses to ganglionic blockade with Ecolid (chlorisondamine chloride) and to graded intravenous injections of angiotensin II and norepinephrine were compared in 6- to 8-wk-old male Zucker rats and their lean controls (n = 10/group). The obese rats exhibited significant hypertension before ganglionic blockade (P less than 0.001), and this difference was largely sustained during ganglionic blockade (P less than 0.005). Furthermore, the obese rats exhibited greater pressor sensitivity to both angiotensin II and to norepinephrine during ganglionic blockade (P less than 0.01). Thus enhanced pressor sensitivity, independent of sympathetic neural activity, appears to support hypertension in Zucker obese rats.