ADRENOCEPTOR INVOLVEMENT IN THE CARDIOVASCULAR-RESPONSES TO B-HT 920 IN SINOAORTIC DENERVATED RATS

1. A study was made relating the involvement of alpha-adrenoceptors in the cardiovascular responses to intracerebroventricular (ICV) injecti on of B-HT 920, a clonidine-type drug, in conscious sham-operated and sinoaortic-denervated rats. 2. Wister rats were used, 7 days after the sham operation or sinoaortic denervation. For ICV injection of drugs, a guide cannula had been previously implanted in the left lateral ven tricle. 3. In sham operated rats, cardiovascular responses to B-HT 920 (10-60 mu g) were increased blood pressure and bradycardia; but, in s inoaortic-denervated rats, after the presser response, a decrease in b lood pressure also was seen. The responses to this agent were greater in sinoaortic-denervated rats than in sham-operated animals. Treatment with the alpha(2)-adrenoceptor antagonist yohimbine (30 mu g), the im idazoline receptor antagonist idazoxan (15 mu g) and the alpha(1A)-adr enoceptor antagonist 5-methylurapidil (15 pg) blocked the responses to B-HT 920 (30 mu g). The alpha(1)-adrenoceptor antagonist prazosin (15 mu g) and the alpha(1B)-adrenoceptor antagonist chloroethylclonidine (100 mu g) did not modify the responses to agonist. 4. Sinoaortic dene rvation enhances the cardiovascular responses to B-HT 920. Moreover, t he effects of ICV administration of B-HT 920 could be mediated by seve ral types of brain receptors: imidazoline receptors and alpha(1A)- and alpha(2)-adrenoceptors. (C) 1998 Elsevier Science Inc.