Possible dependence of pressor and heart rate effects of NG‐nitro‐l‐arginine on autonomic nerve activity

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Abstract
1 The effects of NG-nitro-l-arginine (l-NNA) on mean arterial pressure (MAP) and heart rate (HR) were investigated in conscious rats. 2 Intravenous bolus cumulative doses of l-NNA (1–32 mg kg−1) dose-dependently increased MAP. Both mecamylamine and phentolamine increased MAP responses to l-NNA, angiotensin II and methoxamine. Propranolol, reserpine, atropine and captopril did not affect MAP response to l-NNA. 3 A significant negative correlation of HR and MAP responses to l-NNA was obtained in control rats but not in rats pretreated with reserpine or mecamylamine. Significant negative correlations also occurred in the presence of atropine, propranolol, phentolamine or captopril. 4 A single i.v. bolus dose of l-NNA (32 mg kg−1) raised MAP to a peak value of 53 ± 3 mmHg and the effect lasted more than 2 h; the rise and recovery of MAP were accompanied by significant decrease and increase in HR, respectively. While both phentolamine and mecamylamine increased peak MAP response to l-NNA, mecamylamine abolished the biphasic HR response and phentolamine potentiated the bradycardic component of HR. 5 Blockade of the autonomic nervous and renin-angiotensin systems did not attenuate the pressor effects of l-NNA. However, the biphasic HR response to l-NNA is mediated via modulation of autonomic nerve activities.