Published data revealed that Ang II could have either vasoconstrictor or vasodilatator effects depending on the species or experimental conditions. The present study examined the vasomotor effects of angiotensinogen (Aogen), Ang I and Ang II on rat renal artery rings (RAR) using two experimental models. In the first one, the different doses of Aogen, Ang I and Ang II was administered before cumulative administration of phenylephrine (10nM - 10microM, Phe). In the second experimental model, the RAR were precontracted with Phe (10microM) and the relaxant responses to cumulative concentration of Aogen, Ang I and Ang II (1nM – 10microM) were subsequently studied. The experiments were carrying out in the absence and in the presence of losartan (10microM, LOS) or PD123319 (10microM). The pretreatment of RAR with Ang I (100nM) or Ang II (10nM) potentiated the Phe – induced contractile effects, by an AT2 – mediated mechanism. High doses of Ang II (1 or 10 microM) reduced the Emax of Phe – induced contractions with more than 20%; this Ang II effects were blocked by LOS pretreatment. All studied angiotensins had relaxing effects. The order of potency was: Ang II > Ang I >> Aogen. The relaxant effects of Ang I and Ang II were decreased by PD123319 pretreatment but were not significantly modified by endothelial removement. In conclusion, the angiotensins could have either AT1 – mediated contractile effects or AT2 – dependent but endothelium – independent relaxing effects.

Key words: 

angiotensinogen, angiotensin I, angiotensin II, renal artery