INFLUENCE OF SYMPATHETIC BLOCKADE ON THE ACUTE HYPERTENSIVE RESPONSE TO AORTIC CONSTRICTION

The objective of the present study was to determine the contribution o f the sympathetic nervous system to the hypertensive response to acute (45-min) aortic coarctation in conscious intact or sinoaortic-denerva ted (SAD) rats. Rats were treated chronically (5 wk) with guanethidine (50 mg.kg(-1).day(-1) ip) to induce sympathetic nerve degeneration or acutely with the alpha(1)-adrenergic receptor antagonist prazosin (1 mg/kg iv). Aortic constriction elicited a prompt and sustained rise in mean carotid pressure that was significantly greater in SAD than in i ntact rats. The increase in pressure was associated with reflex bradyc ardia only in the intact rats, whereas the heart rate of SAD rats did not change. Guanethidine treatment did not affect the arterial pressur e or heart rate responses to aortic coarctation of intact rats but blu nted the hypertensive response of SAD rats to the same values exhibite d by intact rats. Prazosin administered 10 min after the beginning of aortic coarctation reduced the hypertensive response of SAD rats to th e same level as that of intact rats. In conclusion, the data obtained by means of the association of sinoaortic deafferentation with chronic sympathectomy with guanethidine or acute alpha(1)-adrenergic receptor blockade with prazosin indicate that the greater hypertensive respons e of SAD rats involves a lack of suppression of the sympathetic activi ty in the maintenance of the rise in pressure elicited by aortic coarc tation.