EVIDENCE THAT THE AUTONOMIC NERVOUS-SYSTEM PLAYS A MAJOR ROLE IN THE L-NAME INDUCED HYPERTENSION IN CONSCIOUS RATS

The present study was designed to investigate the role of the autonomi c nervous system in experimental hypertension induced by chronic admin istration of N-nitro-L-arginine methyl ester (L-NAME) in the drinking water (1 mg/mL) over 6 days. L-NAME ingestion caused a large rise in r esting mean arterial pressure (MAP) (175 +/- 5 mm Hg) and heart rate ( HR) (440 +/- 17 beats per minute) compared to nontreated control rats (resting MAP: 112 +/- 2 mm Hg and HR: 345 +/- 8 beats per minute). Gan glionic blockade induced by trimethaphan (5 mg/kg, intravenously) caus ed a significantly (P < .01) greater decrease in MAP (DELTA - 86 +/- 7 mm Hg) compared to control rats MAP (DELTA - 44 +/- 4 mm Hg). This st rongly suggests that the level of central sympathetic tone in L-NAME - treated rats is much greater than in nontreated rats. Using atenolol and atropine alone and combined, the level of resting sympathetic driv e to the heart was found to be significantly increased in L-NAME - tre ated rats compared to control rats. However, vagal tone to the heart w as found to be virtually abolished in L-NAME - treated rats compared t o control rats. These results indicate that an increase in central sym pathetic drive plays an important role in the hypertension induced by chronic inhibition of nitric oxide synthesis with L-NAME.