Interactions between extracellular and intracellular administered angiotensin II in isolated rat portal vein rings

It is already demonstrated that intracellular angiotensin II (Ang II) stimulates smooth muscle contraction and cell growth. We studied the contractile effects of Ang II intracellular delivered by the means of liposomes (LAngII) and also the interactions between intracellular and extracellular administered Ang II on the rat portal vein rings without endothelium. The results were expressed as the percentages of the control contraction (K+ 40 mM; mean +/- S.E.M). LAngII induced contractions were of 120.46 +/- 8.06%. On the other hand, 0.1 microM Ang II produced contractions of 121.43 +/- 6.83%. Both Ang II and losartan, administered either extracellular in the organ bath or intracellular by the means of liposomes, inhibited the contractions induced by intracellular Ang II. The inhibitory effects of losartan on LAngII-induced contractions were dose-dependent. Thus, 10 microM losartan strongly blocked (10.01 +/- 1.41%) and 1 microM losartan partially blocked (39.73 +/- 5.35%) the LAngII-induced effects. LLOS significantly inhibited the LAngII contractile effects (38.51 +/- 8.92%). Our results revealed that LAngII partially inhibited the contractions induced by extracellular administered Ang II (42.42 +/- 3.29%). On the other hand, 0.1 microM Ang II also inhibited the contractile effects induced by LAngII (67.42 +/- 0.76%), although a little bit less. So, contractions induced by Ang II administered intracellular are mainly mediated by intracellular Ang II receptors sensitive to losartan. At the same time, the participation of cell membrane angiotensin receptors to intracellular Ang II effects cannot be excluded.