Effect of angiotensin II on body fluid volume of the freshwater oligochaete Tubifex tubifex via the angiotensin II receptor

Angiotensin (Ang) II upregulates body fluid volume in vertebrates; however, it produces varying effects in invertebrates. Ang II upregulates body fluid volume in clam worms and slugs (marine and terrestrial organisms), but downregulates it in blood-sucking leeches. It has been unclear whether the downregulating effect of Ang II in leeches is caused by their blood-feeding behavior. We investigated the effects of Ang I and Ang II on body fluid volume in the freshwater sludge worm, Tubifex tubifex (Annelida, Oligochaeta, Tubificidae), which does not require blood-feeding. T. tubifex worms were exposed to Ang I or Ang II dissolved in artificial pond water. Ang II decreased the body weight of the worms in a time- and dose-dependent manner, whereas Ang I had no effect. To determine if the Ang II receptors were involved in this Ang II-induced effect, the worms were treated with the nonselective Ang II receptor inhibitor, saralasin. Saralasin inhibited Ang II-induced body weight loss. Bovine-type saralasin, [Sar1, Val5, Ala8]-Ang II, exhibited a greater inhibitory effect on body weight loss than human-type saralasin, [Sar1, Ala8]-Ang II. These results indicate that Ang II, in contrast to the effect in vertebrates and some other invertebrates, reduces the body fluid volume of T. tubifex via the Ang II receptor. The findings will help to evolutionarily evaluate functions of the renin-angiotensin system in mammals.