DIFFERENTIAL-EFFECTS OF CENTRAL TREATMENT WITH PERTUSSIS TOXIN ON CARDIOVASCULAR-RESPONSES TO CLONIDINE, 8-OH-DPAT AND QUINPIROLE IN CONSCIOUS RATS

The role of guanine nucleotide binding proteins (G-proteins) in central cardiovascular regulation was studied by testing blood pressure and heart rate responses to different drugs in conscious, chronically instrumented spontaneously hypertensive rats (SHR) one day before and one day after central treatment with 2 mug pertussis toxin (PTX). In control SHR, the i.v. injection of clonidine (0.01 mg/kg) or 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (0.1 mg/kg) caused a decrease in blood pressure and heart rate, while injection of quinpirole (0.3 mg/kg) caused an increase in blood pressure. The i.v. injection of nitroprusside, nifedipine or hydralazine induced a decrease in blood pressure and tachycardia. After treatment with PTX, the effects of clonidine and quinpirole on blood pressure were significantly attenuated, but the bradycardic response to 8-OH-DPAT was significantly enhanced. Quinpirole caused an increase in heart rate in PTX-treated SHR. The effect on blood pressure of injections of nitroprusside, nifedipine or hydralazine was not influenced by PTX. The tachycardia caused by injection of nifedipine was enhanced. These results show that G-proteins play a role in the central cardiovascular effect of clonidine, 8-OH-DPAT and quinpirole. Moreover, the treatment with PTX may influence central baroreflex-mediated responses.