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 baroreceptor 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(1 mmHg=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.
The present study was designed to investigate the effect of microinfusion anglotensin Ⅱ (Ang Ⅱ ),Ang Ⅱ type l(AT1)receptor antagonist lesartan into the rostral ventrolateral medulla(RVLM)on the baroreceptor 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(0.5μl/h), Ang Ⅱ(1.Snmol/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 arteriaI pressutre [ MAP,mmHg(1 mmHg = 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 ][ was almost completely abolished by pretreatment with microinjection of losartan. Conc/us/on: These results showed that the exogenous Ang II in the RVLM produces inhibitory modulation of BRS, which is mediated by AT2 receptor.However,AT1 receptor in the RVLM is not involved in the tonic control of BRS.
基金
supportedbygrantsfromJiangsuProvincialDepartmentofEducation(0 3KJD3 2 0 14 6andQingLanProject)andfromNanjingMedicalUniversity(NY0 2 0 81)
