Effect of Microinfusion of Angiotensin Ⅱ into the RVLM in Rats on the Baroreceptor Reflex Sensitivity

摘要

Objective: The present study was designed to investigate the effect of microinfusion angiotensin Ⅱ (Ang Ⅱ), Ang Ⅱ type 1(AT_1) receptor antagonist losartan into the rostral ventrolateral medulla (RVLM) on the barore-ceptor reflex sensitivity(BRS) in urethane-anesthetized rats. Methods: Reflex changes in heart rate(HR) were elicited by bolus intravenous injection of phenylephrine before and during RVLM microinfusion of saline(0.5 μl/h), Ang Ⅱ (1.5 nmol/h), losartan (250 nmol/h), and Ang Ⅱ (1.5 nmol/h) pretreated with microinjection of losartan (50 nmol/0.51 μl) into the RVLM. The average ratio between changes in HR in beats per minute(beats · min~(-1)) and changes in mean arterial pressure [MAP, mmHg(1mmHg = 0.133 kPa)] was used as an index of BRS. Results: Ang Ⅱ resulted in a significant decrease in the BRS for reflex bradycardia compared with control ( -2.1 +- 0.1 vs -3.9 +- 0.4 beats · min~(-1) · mmHg~(-1)). Microinfusion of losartan had no significant effect on BRS for reflex bradycardia. The effect of Ang Ⅱ was almost completely abolished by pretreatment with microinjection of losartan. Conclusion: These results showed that the exogenous Ang Ⅱ in the RVLM produces inhibitory modulation of BRS, which is mediated by AT_1 receptor. However, AT_1 receptor in the RVLM is not involved in the tonic control of BRS.