Exaggerated Bezold-Jarisch reflex in the hypertension induced by inhibition of nitric oxide synthesis

ABSTRACT

The present study was designed investigate the role of cardio-pulmonary reflex, more specifically the bezold-Jarisch reflex, in experimental hypertension induced by chronic administration of Nw-nitro-L-arginine methyl ester (L-NAME) (0,5 mg/ml) added to the drinking water for 6 days. The study was perfomed in male Wistar rats (200-350 g), 9 animals per group. L-NAME ingestion caused a significant increase in resting mean arterial pressure (MAP: 182 + or - 4mmHg) and heart rate (HR: 447 = or - 20 bpm) when compared to untreated rats (MAP: 112 = or - 3 mmHg and HR: 355 + or - 10 bpm). Cardiopulmonary receptors were chemically stimulated with bolus injections of 5-hydroxytryptamine (5-HT, 4-10 ug/Kg, iv) followed by measuring the falls in diastolic arterial pressure (DAP) and HR in conscious and freely moving animals. An expected, the responses to intravenous injections of 5-HT consisted of a dose-dependent reduction in HR (from 26 = or - 14 to 175 + or - 25 bpm) and DAP (from 7 + or - 4 to 39 + or - 3 mmHg) in the control rats. Both bradycardia and diastolic hypotension were significantly accentuated in the L-NAME animals (approximately 30 per cent). These data suggest that, in contrast to other models of hypertension, in the present one caused by inhibition of nitric oxide synthesis, the Bezold-Jarisch reflex exaggerated. This neural dysfunction could be related to changes in the cardiac vagal effrent or effector