AT1 receptors in the RVLM mediate pressor responses to emotional stress in rabbits

In this study, we examined the role of angiotensin type 1 (AT(1)) receptors in the rostral ventrolateral medulla (RVLM) in mediating the pressor action of emotional stress in conscious rabbits. Rabbits were chronically instrumented with guide cannulas for bilateral microinjections into the RVLM and an electrode for measuring renal sympathetic nerve activity (RSNA). Airjet stress evoked increases in arterial pressure, heart rate, and RSNA, which reached a maximum (+9+/-1 mm Hg, +20+/-5 beats/min, and +93+/-17%, respectively) in the first 2 minutes of stress exposure. Then RSNA rapidly returned to prestress values, while arterial pressure and heart rate remained close to the maximal level until the conclusion of the 7-minute airjet exposure. Microinjections of the nonselective angiotensin receptor antagonist sarile (0.5 nmol, n=8) or AT(1) receptor antagonists losartan (2 nmol, n=6) or candesartan (0.2 nmol, n=6) into the RVLM did not alter resting cardiovascular parameters. By contrast, the antagonists attenuated the sustained phase (4 to 7 minutes) of the pressor stress response by 55% to 89%. However, only sarile decreased the onset of this response. The antagonists affected neither the stress-induced tachycardia nor the pressor response to glutamate microinjections. Microinfusion of angiotensin II (4 pmol/min, n=8) into the RVLM did not change the pressor response to airjet stress but attenuated tachycardic response by 47%. Microinjections of vehicle did not alter the cardiovascular stress response. Sarile, losartan, and angiotensin II did not affect the sympathoexcitatory response to baroreceptor unloading. These results suggest that AT(1) receptors in the RVLM are important in mediating the pressor effects of emotional stress in conscious rabbits.