Nitric oxide and angiotensin II receptors mediate the pressor effect of angiotensin II: a study in conscious and zoletil-anesthetized rats.

Background: The circumventricular structures of the central nervous system and nitric oxide are involved in arterial blood pressure control, and general anesthesia may stimulate the central renin-angiotensin system. We therefore investigated the central role of angiotensin II and nitric oxide on the regulation of systemic arterial blood pressure in conscious and anesthetized rats.

Methods: Rats with stainless steel cannulae implanted into their lateral ventricle were studied. We injected the AT1 and AT2 angiotensin II receptor antagonists, losartan and PD123319, L-NAME, 7-nitroindazole (nitric oxide synthetase inhibitors), and FK409 (nitric oxide donor agent) into the lateral ventricles. Mean arterial blood pressure (MAP) was recorded in conscious and zoletil-anesthetized rats.

Results: Mean +/- sem baseline MAP was 117.5 +/- 2 mm Hg. Angiotensin II injected into the brain lateral ventricle increased MAP from 136.5 +/- 2 mm Hg to 138.5 +/- 4 mm Hg (Delta16 +/- 3 mm Hg to Delta21 +/- 3 mm Hg) for all experimental groups versus control from 116 +/- 2 mm Hg to 120 +/- 3 mm Hg (Delta3 +/- 1 mm Hg to Delta5 +/- 2 mm Hg) (P < 0.05). L-NAME or 7-nitroindazole enhanced the angiotensin II pressor effect (P < 0.05). Prior injection of losartan and PD123319 decreased the angiotensin II pressor effect and the enhancement effect of L-NAME and 7-nitroindazole (P < 0.05). Zoletil anesthesia did not interfere with the effects of angiotensin II, AT1, AT2 antagonists, or nitric oxide synthetase inhibitors.

Conclusions: Endogenous nitric oxide functions tonically as a central inhibitory modulator of the angiotensinergic system. AT1 and AT2 receptors influence the angiotensin II central control of arterial blood pressure. Zoletil anesthesia did not interfere with these effects.