Conversion of brain angiotensin II to angiotensin III is critical for pressor response in rats

Abstract

The present investigation measured the relative pressor potencies of intracerebroventricularly infused ANG II, ANG III, and the metabolically resistant analogsd-Asp¹ANG II andd-Arg¹ANG III in alert freely moving rats. The stability of these analogs was further facilitated by pretreatment with the specific aminopeptidase A inhibitor EC33 or the aminopeptidase N inhibitor PC18. The results indicate that the maximum elevations in mean arterial pressure (MAP) were very similar for each of these compounds across the dose range 1, 10, and 100 pmol/min during a 5-min infusion period. However, d-Asp¹ANG II revealed significantly extended durations of pressor effects before return to base level MAP. Pretreatment intracerebroventricular infusion with EC33 blocked the pressor activity induced by the subsequent infusion of d-Asp¹ANG II, whereas EC33 had no effect on the pressor response to subsequent infusion ofd-Arg¹ANG III. In contrast, pretreatment infusion with PC18 extended the duration of thed-Asp¹ANG II pressor effect by about two to three times and the duration of d-Arg¹ANG III's effect by ∼10 to 15 times. Pretreatment with the specific AT₁receptor antagonist losartan blocked the pressor responses induced by the subsequent infusion of both analogs indicating that they act via the AT₁receptor subtype. These results suggest that the brain AT₁receptor may be designed to preferentially respond to ANG III, and ANG III's importance as a centrally active ligand has been underestimated.