Hemodynamic effect produced by microinjection of angiotensins at the caudal ventrolateral medulla of spontaneously hypertensive rats

Abstract

In the present study, the effect of caudal ventrolateral medulla (CVLM) microinjection of angiotensin-(1-7) (Ang-(1-7)) and angiotensin II (Ang II) on mean arterial pressure (MAP), heart rate (HR) and pulsatile vascular blood flow (VBF; Transonic System) of the femoral, renal or mesenteric arteries was evaluated in male Wistar and spontaneously hypertensive rats (SHR) anesthetized with urethane. The vascular resistance (VR) was calculated by the ratio between the changes in MAP and VBF. Ang-(1-7) (40 ng) and Ang II (40 ng) microinjection into the CVLM caused similar depressor effects in Wistar rats and SHR. The hypotensive effect produced by Ang-(1-7) into the CVLM of Wistar rats was accompanied by a decrease in femoral (ΔVR/VRbaseline=−0.12±0.04 vs. 0.001±0.03; after saline) and renal (ΔVR/VRbaseline=−0.10±0.02 vs. −0.003±0.02; after saline) vascular resistance. On the other hand, the Ang II hypotensive effect in Wistar rats produced only changes in renal vascular resistance (ΔVR/VRbaseline=−0.16±0.02 vs. −0.003±0.02; after saline). In SHR, the hypotensive effect produced by Ang-(1-7) and Ang II caused decrease in renal vascular resistance (ΔVR/VRbaseline=−0.18±0.03 and −0.13±0.01, respectively, as compared with saline, ΔVR/VRbaseline=−0.06±0.02), but did not alter the femoral or mesenteric vascular resistance. These data show that Ang II and Ang-(1-7) hypotensive effect at the CVLM involves the participation of different vascular beds. Further, the lack of involvement of the femoral vascular bed in SHR suggests that hypertension may induce alteration in the neural control of the different vascular beds, at least at the CVLM.