New approach for measurement of sympathetic nervous abnormality in conscious, spontaneously hypertensive rats

We previously reported a highly sensitive chemiluminescence high-performanc e liquid chromatographic method to determine catecholamines in plasma. In t his study, we employed this method to measure the cardiac function and plas ma norepinephrine (NE) concentration in conscious rats. Benidipine, 1,4-dih ydropyridine calcium antagonist (4 mg/kg), and beta-blocker (propranolol, 3 0 mg/kg) were administered orally to conscious spontaneously hypertensive r ats (SHRs) and Wistar-Kyoto (WKY) rats, and blood pressure, heart rate and plasma NE levels were measured. Plasma NE concentration was used as an inde x of sympathetic nervous system activity in conscious rats. The basal plasm a NE levels were significantly higher in SHRs than in WKY rats (P<0.05), in dicating the activity of the basal sympathetic nervous system in SHRs was e levated. The sensitivity of the baroreflex-mediated sympathetic nervous res ponse was reduced in SHRs as compared to that in WKY rats. The concomitant administration of benidipine and a beta-blocker decreased heart rate withou t affecting the baroreflex-mediated sympathetic nervous response, indicatin g that propranolol might suppress mainly the cardiac beta-adrenoceptor. The present study suggested the high activity of the basal sympathetic nervous system and the reduced response of the baroreflex-mediated sympathetic ner vous system in SHRs compared to WKY rats in the conscious condition.