Functional evidence that the central renin-angiotensin system plays a role in the pressor response induced by central injection of carbachol.

We investigated the effects of losartan, an AT1-receptor blocker, and ramipril, a converting enzyme inhibitor, on the pressor response induced by angiotensin II (ANG II) and carbachol (a cholinergic receptor agonist). Male Holtzman rats (250-300 g) with a stainless steel cannula implanted into the lateral ventricle (LV) were used. The injection of losartan (50 nmol/1 microliter) into the LV blocked the pressor response induced by ANG II (12 ng/1 microliter) and carbachol (2 nmol/1 microliter). After injection of ANG II and carbachol into the LV, mean arterial pressure (MAP) increased to 31 +/- 1 and 28 +/- 2 mmHg, respectively. Previous injection of losartan abolished the increase in MAP induced by ANG II and carbachol into the LV (2 +/- 1 and 5 +/- 2 mmHg, respectively). The injection of ramipril (12 ng/1 microliter) prior to carbachol blocked the pressor effect of carbachol to 7 +/- 3 mmHg. These results suggest an interaction between central cholinergic pathways and the angiotensinergic system in the regulation of arterial blood pressure.