Biojournal of Science and Technology
Volume 3, ISSN:2410-9754, Article ID: m150005

Research Article

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

Tsutomu Nakagawa1,2,*, Ryousuke Satou2,†, Yusuke Oda1, Fumiaki Suzuki1,2, Yukio Nakamura1,2

Date of Acceptance: 2016/03/08
Published in Online: 2016/03/20

1 Department of Applied Life Science, Faculty of Applied Biological Sciences, Gifu University, Gifu, Japan 2 United Graduate School of Agricultural Science, Gifu University, Gifu, Japan
Address Correspond to:
Tsutomu Nakagawa Department of Applied Life Science, Faculty of Applied Biological Sciences, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan E-mail: [email protected]

Academic editor: Editor-in-Chief

To Cite This Article:
Tsutomu Nakagawa, Ryousuke Satou, Yusuke Oda, Fumiaki Suzuki, Yukio Nakamura. Effect of angiotensin II on body fluid volume of the freshwater oligochaete Tubifex tubifex via the angiotensin II receptor. Biojournal of Science and Technology. Vol:3, 2016

Download PDF | Citation Download | Views: [wpstatistics stat=pagevisits time=total]

Abstract

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.

Authors Link:
, , , ,

Content Section

INTRODUCTION

The renin-angiotensin system is important in the regulation of blood pressure, body fluid homeostasis, and renal, neuronal, and endocrine functions associated with cardiovascular control in vertebrates (Inagami T, 1994). Renin, the rate-limiting enzyme of the renin-angiotensin system, hydrolyzes its specific protein substrate angiotensinogen to release the decapeptide angiotensin (Ang) I, which is further cleaved by a nonspecific dipeptidyl-carboxypeptidase angiotensin-converting enzyme (ACE) to produce the vasopressor octapeptide Ang II. Ang II functions by binding to Ang II type-1 (AT1) and type-2 (AT2) receptors.

A renin-like enzyme, an angiotensinogen-like protein, and ACE have been discovered in invertebrates such as leeches (Salzet and Stefano, 1997; Salzet et al., 1993; Vandenbulcke et al., 1997), locusts (Salzet et al., 2001; Schoofs et al., 1998; Veelaert et al., 1998), molluscs (Gonzalez et al., 1995; Laurent et al., 1997), and crabs (Delorenzi et al., 1996). Ang II-amide was isolated from leeches (Salzet et al., 1995), and immunoreactivity against anti-Ang I or anti-Ang II antibodies was demonstrated in leeches (Salzet et al., 2001), clam worms (Fewou and Dhainaut-Courtois, 1995), locusts (Schoofs et al., 1998), and crabs (Delorenzi et al., 1996; Frenkel et al., 2010). A 140-kDa protein with immunoreactivity to anti-AT1 receptor antibodies was purified from leech coelomocyte extract using an Ang II affinity column (Salzet and Verger-Bocquet, 2001). These findings suggest that invertebrates express essential components of the renin-angiotensin system.

There are some reports demonstrating the effects of Ang II on body fluid homeostasis in invertebrates. In the clam worm, a marine polychaete, Ang II attenuates body fluid loss under hyperosmotic and drying conditions and enhances body fluid gain under hypoosmotic conditions (Fewou and Dhainaut-Courtois, 1995; Satou et al., 2005a; Satou et al., 2005b). In slugs, Ang II facilitates water absorption from the foot (Makra and Prior, 1985). Accordingly, Ang II increases body fluid volume in these invertebrates as well as in vertebrates. In contrast to the physiological action of Ang II in the aforementioned invertebrates, Ang II accelerates body fluid loss under semidrying conditions in leeches (Salzet et al., 1995; Salzet et al., 1992), suggesting a negative regulation of body fluid volume by Ang II. However, it was concluded that the downregulating effect of Ang II in leeches was caused by their blood-feeding behavior. Therefore, in the present study, we tested if Ang II decreases body fluid volume in a freshwater oligochaete, Tubifex tubifex, which does not require blood-feeding.

MATERIALS AND METHODS
Reagents
Ang I, Ang II (human type), [Sar1, Ala8]-Ang II (saralasin, human type), and [Sar1, Val5, Ala8]-Ang II (saralasin, bovine type) were purchased from the Peptide Institute (Osaka, Japan). Other chemical reagents were from Nacalai Tesque (Kyoto, Japan).

Animals
Freshwater sludge worms, T. tubifex (Annelida, Oligochaeta, Tubificidae) collected from a natural source were obtained from a local aquarium fish supplier in Gifu, Japan, and maintained at room temperature in artificial pond water (APW; Dietz and Alvarado, 1970) consisting of 0.5 mM NaCl, 0.05 mM KCl, 0.4 mM CaCl2, and 0.2 mM NaHCO3 until use. When the worms were used for the experiments, we carefully observed the morphology of individual animals and excluded worms which exhibited unexpected size and/or morphology.

Treatment of T. tubifex with Ang I or Ang II

  1. tubifex worms (a total of approximately 100 mg) were exposed at room temperature to Ang I (from 0 to 1 × 10-8 M) or Ang II (from 0 to 1 × 10-7 M) dissolved in APW for 30 min. The total body weight of the worms was measured after briefly blotting on tissue paper to remove external liquid. The total body weight was expressed as a relative value to that observed at the 0-min time point of each treatment.
  1. tubifex worms (a total of approximately 100 mg) were exposed to 1×10-8 M Ang I or Ang II dissolved in APW at room temperature. APW, which does not contain Ang, served as a control. The total body weight of the worms was measured and expressed as described above after treatment times of 0, 15, 30, and 60 min.

Treatment of T. tubifex with Ang II in the presence of varying concentrations of saralasin T. tubifex worms (a total of approximately 100 mg) were exposed at room temperature to 1×10-8 M Ang II in combination with 0 to 1×10-8 M human- or bovine-type saralasin in APW for 30 min. The total body weight of the worms was measured and expressed as described above.

Statistical analysis
Data were expressed as mean ± SD of three independent experiments. Statistical comparison was performed by Welch’s t-test using Statcel (OMS, Japan). A p-value less than 0.05 was considered significant.

RESULTS
Effects of varying concentrations of Ang I and Ang II on body weight of T. tubifex Ang II produced a decrease in body weight of T. tubifex in a concentration-dependent manner (Figure 1). Significant changes were observed at 1 × 10-12 to 1 × 10-7 M. The maximal and the half-maximal effect of Ang II were observed at about 1 × 10-8 and 2-5 × 10-11 M, respectively. Ang I did not alter the body weight.

Figure 1. Effects of Ang I and Ang II on the body weight of Tubifex tubifex. The worms were treated with indicated concentrations of Ang I (open circle) or Ang II (closed circle) in artificial pond water (APW) for 30 min. Data are expressed as mean ± SD of three independent experiments. Asterisks indicate a significant difference compared to the value obtained in the absence of Ang at *p < 0.05 or **p < 0.01.

Temporal changes in the body weight of T. tubifex treated with/without Ang II

In the control group exposed to APW, approximately 5% of body weight was lost after 60 min. Treatment with Ang II (1 × 10-8 M) enhanced the decrease in body weight in a time-dependent manner (Figure 2). Body weight markedly decreased to below 85% during the first 30 min of the treatment, and then, the decreased body weight was sustained in the following 30 min. Ang I-treated worms did not show any difference from the control.

Effect of saralasin on Ang II-induced change in body weight of T. tubifex
Both human- and bovine-type saralasins blunted the Ang II-induced body weight loss (Figure 3). Saralasins at 1 × 10-9 and 1 × 10-8 M recovered the body weight to the control level. The half-maximal inhibitory concentrations for human- and bovine-type saralasins were 2–3 × 10-10 and 4–5 × 10-11 M, respectively.

Figure 2. Temporal changes in the body weight of Tubifex tubifex treated with/without Ang II. The worms were treated with 1 × 10-8 M Ang I (open circle) or Ang II (closed circle) in artificial pond water (APW) up to 60 min. APW without Ang was used as a control (open triangle). Data are expressed as mean ± SD of three independent experiments. Asterisks indicate a significant difference compared to the value at the 0-min time point at *p < 0.05 or **p < 0.01.

Figure 3. Effect of saralasin on the Ang II-induced change in body weight of Tubifex tubifex. The worms were treated with 1×10-8 M Ang II in combination with 0 to 1×10-8 M human-type (closed circle) or bovine-type (open triangle) saralasin in artificial pond water (APW) for 30 min. Data are expressed as mean ± SD of three independent experiments. Asterisks indicate a significant difference compared to the value obtained in the absence of saralasin at *p < 0.05 or **p < 0.01. The dotted line represents the mean value obtained from the worms treated with APW for 30 min in the absence of Ang and saralasin.

DISCUSSION
Ang II produced a time- and concentration-dependent decrease in body weight in T. tubifex, suggesting that Ang II downregulates the body fluid volume of the worms. This effect in T. tubifex resembles the diuretic effects of Ang II in the leech Theromyzon tessulatum (Salzet et al., 1995); however, it is not consistent with the upregulating effects on body weight in clam worms Nereis diversicolor and Perinereis sp. (Fewou and Dhainaut-Courtois, 1995; Satou et al., 2005a; Satou et al., 2005b), and in vertebrates. The differing effects of Ang II in invertebrates may have originated from evolutionary adaptations to environmental conditions. Considered together with the findings presented above, Ang II seems to upregulate the body fluid volume in invertebrates that undergo the passive outflow of body fluid water (e.g., marine and terrestrial organisms), but downregulate the body fluid volume in invertebrates that utilize the passive or active inflow of outside water to regulate body fluid volume (e.g., freshwater and blood-feeding organisms).

In the present study, the Kd value of Ang II for its receptor estimated from the concentration-dependence curve (Figure 1) was 2–5 × 10-11 M, which is a similar order to that reported in clam worms (Satou et al., 2005a) and mammals (Kobayashi and Takei, 1996). The minimum effective concentration of Ang II observed in this study was 1 × 10-12 M, supporting previous findings in clam worms (Satou et al., 2005a). In addition, the minimum effective concentration of Ang II in T. tubifex is similar to the human and rat plasma concentration of the peptide (Jacobsen and Poulsen, 1990; Matsui et al., 1999; Mizuno et al., 1992). Since these results suggest the existence of an Ang II receptor in T. tubifex, involvement of Ang II receptors in Ang II-induced body weight loss in T. tubifex was tested using Ang II receptor inhibitors. Antagonizing properties of pharmacological Ang II receptor blockers including losartan, candesartan, and olmesartan have not been evaluated in invertebrates. Thus, saralasins, Ang II analogs (Regoli et al., 1974; Timmermans et al., 1974), were employed in the study to avoid potential issues with species-dependent specificity of Ang II receptor blockers. The existence of Ang II receptors in T. tubifex is further supported by the observation that saralasin diminished the Ang II-induced effect (Figure 3). The receptor subtype; however, was not delineated in the current study because of the nonselectivity of the antagonist. The use of a specific AT2 receptor antagonist such as PD123319 will clarify the receptor subtype concerning the Ang II-induced effect if the inhibitor is crossreactive with putative AT2 receptors in the worm. The Ki values of human- and bovine-type saralasins for the receptor estimated from the inhibition curves (Figure 3) were 2–3 × 10-10 and 4–5 × 10-11 M, respectively. This suggests higher affinity of the Ang II receptor to bovine-type Ang II than human one. Although human-type Ang II was elucidated in leeches (Salzet et al., 1995), a more bovine-type-like Ang II is speculated in T. tubifex.

Ang I was ineffective even at 1 × 10-8 M, which is 10,000-fold higher than the lowest Ang II concentration that produced significant effects. As ACE is a nonspecific dipeptidyl-carboxypeptidase, this result suggests the possibility that Ang II acts cutaneously and is not taken up into the body fluid of the worm. This possibility is supported by the finding that Ang II affects frogs through skin exposure (Coviello and Brauckmann, 1973). In addition, ACE, which does not contain a C-terminal transmembrane domain, has been identified in leeches and other invertebrates (Rivière et al., 2004). The expression of only soluble ACE in invertebrates might also provide limited capability of local production of Ang II from exogenous Ang I in the present study.

In conclusion, Ang II downregulates body fluid volume of T. tubifex via the Ang II receptor, providing evidence that Ang II downregulates body fluid volume of non-blood-feeding invertebrates. Although further studies including identification of the components of the renin-angiotensin system will be required to elucidate the physiological significance of this hormonal system in course of evolution, the findings will help to evolutionarily evaluate functions of the renin-angiotensin system in mammals.

ACKNOWLEDGMENTS
We thank Prof. Takashi Shimizu (Hokkaido University, Sapporo, Japan) for helpful information on tubificid taxonomy, biology, and maintenance.

Reference

  1. Coviello A, Brauckmann ES. Hydrosmotic effect of angiotensin II: isolated toad skin. Acta Physiol Lat Am. 1973, 23: 18-23.
  2. Delorenzi A, Pedreira ME, Romano A, Garcia SI, Pirola CJ, Nahmod VE, Maldonado H. Angiotensin II enhances long-term memory in the crab Chasmagnathus. Brain Res Bull. 1996, 41: 211-220.
  3. Dietz TH, Alvarado RH. Osmotic and ionic regulation in Lumbricus terrestris Biol Bull. 1970, 138: 247-261.
  4. Fewou J, Dhainaut-Courtois N. Research on polychaete annelid osmoregulatory peptide(s) by immunocytochemical and physiological approaches. Computer reconstruction of the brain and evidence for a role of angiotensin-like molecules in Nereis (Hediste) diversicolor OF Müller. Biol Cell. 1995, 85: 21-33.
  5. Frenkel L, Dimant B, Portiansky EL, Imboden H, Maldonado H, Delorenzi A. Neuroanatomical distribution of angiotensin-II-like neuropeptide within the central nervous system of the crab Chasmagnathus; physiological changes triggered by water deprivation. Cell Tissue Res. 2010, 341: 181-195.
  6. Gonzalez GC, Roger I, Gonzalez E, Martinez-Padron M, Moore GJ, Lukowiak K. Angiotensinogen-like epitopes are present in the CNS of Aplysia California and co-localize with urotensin I- and urotensin II-like immunoreactivities in the cerebral ganglia. Neuroreport. 1995, 15: 541-544.
  7. Inagami T. The renin-angiotensin system. Essays Biochem. 1994, 28: 147-164.
  8. Jacobsen J, Poulsen K. In vivo generation and elimination of angiotensin in the rat. Clin Exp Pharmacol Physiol. 1990, 17: 445-451.
  9. Kobayashi H, Takei Y. The renin-angiotensin system: Comparative aspects. Zoophysiology. Vol. 35. Springer, 1996.
  10. Laurent V, Stefano GB, Salzet M, Presence and biochemical properties of a molluscan angiotensin-converting enzyme. Regul Pept. 1997, 69: 53-61.
  11. Makra ME, Prior DJ. Angiotensin II can initiate contact-rehydration in terrestrial slugs. J Exp Biol. 1985, 119: 385-388.
  12. Matsui T, Tamaya K, Kawasaki T, Osajima Y. Determination of angiotensin metabolites in human plasma by fluorimetric high-performance liquid chromatography using a heart-cut column-switching technique. J Chromatogr B Biomed Sci Appl. 1999, 729: 89-95.
  13. Mizuno K, Niimura S, Tani M, Haga H, Gomibuchi T, Sanada H, Fukuchi S. Antihypertensive and hormonal activity of MK 954 in spontaneously hypertensive rats. Eur J Pharmacol. 1992, 215: 305-308.
  14. Regoli D, Park WK, Rioux F. Pharmacology of angiotensin. Pharmacol Rev. 1974, 26:69-123.
  15. Rivière G, Michaud A, Deloffre L, Vandenbulcke F, Levoye A, Breton C, Corvol P, Salzet M, Vieau D. Characterization of the first non-insect invertebrate functional angiotensin-converting enzyme (ACE): leech TtACE resembles the N-domain of mammalian ACE. Biochem J. 2004, 382: 565-573.
  16. Salzet M, Verger-Bocquet M, Wattez C, Malecha J. Evidence for angiotensin-like molecules in the central nervous system of the leech Theromyzon tessulatum (O.F.M.). A possible diuretic effect. Comp Biochem Physiol A. 1992, 101: 83-90.
  17. Salzet M, Wattez C, Baert JL, Malecha J. Biochemical evidence of angiotensin II-like peptides and proteins in the brain of the rhynchobdellid leech Theromyzon tessulatum. Brain Res. 1993, 631: 247-255.
  18. Salzet M, Bulet P, Wattez C, Verger-Bocquet M, Malecha J. Structural characterization of a diuretic peptide from the central nervous system of the leech Erpobdella octoculata. Angiotensin II amide. J Biol Chem. 1995, 270: 1575-1582.
  19. Salzet M, Stefano GB. First biochemical evidence for an enzyme related to mammalian renin in an invertebrate, the leech Theromyzon tessulatum. Mol Cell Endocrinol. 1997, 131: 1-8.
  20. Salzet M, Deloffre L, Breton C, Vieau D, Schoofs L. The angiotensin system elements in invertebrates. Brain Res Mol Brain Res. 2001, 36: 35-45.
  21. Salzet M, Verger-Bocquet M. Elements of angiotensin system are involved in leeches and mollusks immune response modulation. Brain Res Mol Brain Res. 2001, 94: 137-147.
  22. Satou R, Nakagawa T, Ido H, Tomomatsu M, Suzuki F, Nakamura Y. Angiotensin II and III upregulate body fluid volume of the clam worm Perinereis via angiotensin II receptors in different manners. Peptides. 2005a, 26: 2452-2457.
  23. Satou R, Nakagawa T, Ido H, Tomomatsu M, Suzuki F, Nakamura Y. Angiotensin III as well as angiotensin II regulate water flow through aquaporins in a clam worm. Biosci Biotechnol Biochem. 2005b, 69: 1221-1225.
  24. Schoofs L, Veelaert D, De Loof A, Huybrechts R, Issac E. Immunocytochemical distribution of angiotensin I-converting enzyme-like immunoreactivity in the brain and testis of insects. Brain Res. 1998, 785: 215-227.
  25. Timmermans PB, Wong PC, Chiu AT, Herblin WF, Benfield P, Carini DJ, Lee RJ, Wexler RR, Saye J, Smith RD. Angiotensin II receptors and angiotensin II receptor antagonists. Pharmacol Rev. 1974, 45: 205-251.
  26. Vandenbulcke F, Laurent V, Verger-Bocquet M, Stefano GB, Salzet M. Biochemical identification and ganglionic localization of leech angiotensin-converting enzymes. Brain Res Mol Brain Res. 1997, 49: 229-237.
  27. Veelaert D, Schoofs L, De Loof A. Peptidergic control of the corpus cardiacum-corpora allata complex of locusts. Int Rev Cytol. 1998, 182: 249-302.