Effect of angiotensin II on short-circuit current in amphibian membranes

Effects of angiotensin I of the American bullfrog Rana catesbeiana on amphibian tissues

1. The effect of bullfrog angiotensin I [Asp1, Val5, Asn9] angiotensin I, (AT I) on short-circuit current (SCC) on isolated toad skin and aorta contractility was examined. 2. AT I increased SCC in toad skin, the effect was partially inhibited by angiotensin-converting enzyme inhibitor (ACEI) teprotide. 3. AT I induced contractile responses in isolated rings of toad aorta. This effect was partially inhibited by captopril and completely blocked by the peptide antagonist [Sar1, Ile8] angiotensin II. 4. Present results indicate that this homologue AT I would act in amphibian tissues by conversion to AT II.

Stimulatory effect of angiotensin II on electrolyte transport in canine tracheal epithelium

1. The present study examines the effect of angiotensin11 (A11) on Cl- and Na+ transport in canine tracheal epithelium. 2. A concentration-dependent increase in the potential difference and in short-circuit current of the trachea was found. 3. Frusemide reduced values of Cl- dependent electrical parameters; net Cl- flux from serosa to mucosa accounted for 72% of total short-circuit current. 4. Frusemide, indomethacin and chlorpromazine blocked the stimulatory effect of A11. 5. These reactions show that A11 stimulates ion transport across the canine tracheal epithelium and suggest that two mechanisms may be proposed to explain the action of A11 on Cl- flux: (1) Ca(2+)-dependent increase in intracellular cAMP and (2) increase in Na(+)-2Cl2-K+ Cotransport activity.

Stimulatory effect of angiotensin II on the electric properties of the isolated toad skin

In 1982 we showed that angiotensin II (Agt II) stimulates the bioelectric properties of the isolated toad skin and that this effect is blocked by pretreatment of the skin with indomethacine [J. B. Concha et al., IRCS Med. Sci. 10, 584 (1982)]. Ussing's technique and several inhibitors were used to continue this study on the isolated Pleurodema thaul skin. Serosal Agt II produced a dose-dependent increase in electrical parameters: a maximal concentration of 6 X 10(-6) M Agt II increased potential difference by 43 +/- 7.8% and short-circuit current by 51.5 +/- 7.7%. The responses were not affected by either alpha or beta blockers or by atropine. Indomethacine blocked responses to the calcium ionophore A23187 and to Agt II which were similar to each other. Additive effects of Agt II and of the calcium ionophore A23187 were found. No response to Agt II was obtained when Ca2+-free Ringer was used on the serosal side. Calcium channel blockers (nifedipine, verapamil, manganese), pentobarbitone and saralasin blocked the response to Agt II. This pharmacological evidence is in favour of the hypothesis that Agt II activates specific membrane receptors, leading to Ca2+ release and formation of prostaglandins which stimulate adenyl cyclase. This increases cAMP secretion, which in turn increases apical membrane permeability to sodium and enhances the active transport system.

Comparative effects of angiotensin II on osmotic water permeability in the toad (Bufo arenarum)

The possible relationship between the renin-angiotensin system and water balance in the toad Bufo arenarum has been indirectly explored. A positive correlation was found between the hydrosmotic response of ventral pelvic toad skin to angiotensin II (A II) and some age indicators (body weight, snout-urostyle length or head width). A different hydrosmotic response for oxytocin and isoproterenol (but not for A II) was found between four cutaneous regions of toad body. We conclude that A II may not be directly involved in the regulation of water balance mediated by water absorption across the skin of Bufo arenarum toads.

Effects of frog-skin angiotensin II in amphibians

The role of frog-skin angiotensin II (AII) in amphibia was studied by comparing the sodium and water permeability effects of three angiotensins (AII): frog skin (Ala-Pro-Gly-[Ile3, Val5]-Ang II), human [( Asp1, Ile5]-AII), and Japanese goosefish [( Asn1-Val5]-AII). Frog-skin AII increased the short-circuit current (SCC) significantly after it was added to the dermal side of the isolated skin of the South American frogs, Leptodactylus chaquensis and ocellatus, and the toad, Bufo arenarum, in concentrations of 10(-6) M. In frogs, the effect was significant at 15 minutes and reached 45% over control after 2 1/2 hours. The effect cannot be achieved with concentrations lower than 10(-7) M. Since amiloride (10(-4) M) blocked the SCC response, and absence of chloride in the bathing fluid did not, the effect is probably dependent on sodium transport. Human AII (10(-6) M) produced a similar response in summer frogs that had been treated with 0.1% NaCl for 14 days. Goosefish AII was ineffective at similar concentrations, and none of the angiotensins modified SCC in the toad bladder. Hydrosmotic effects could be achieved with the three angiotensins, the response being dependent on seasonal and species factors but always considerably lower than that of the neurohypophyseal peptides. Vascular reactivity of the isolated frog hindlimbs was compared by dose-response curves. Potency ratios on a molar basis against frog-skin AII was 1.136 for human AII and 1.193 for goosefish AII. The results show that the effects of the angiotensins differ in both the response of SCC to frog-skin angiotensin and its higher vascular effects.

Synthesis of nonmammalian angiotensins and their comparative pressor properties in dogfish shark, domestic chicken, and rat

To understand how vertebrates utilize angiotensins during evolutionary development, we undertook studies to synthesize and/or characterize angiotensin-like peptides from nonmammalian species. The present paper describes the synthesis of [Asp1,Val5,Asn9] angiotensin I (bull frog, Rana catesbeiana) (I), [Asn1,Val5,His9] angiotensin I (Japanese goosefish, Lophius litulon) (II), [Asn1, Val5,Asn9] angiotensin I (chum salmon, Oncorhynchus keta) (III), and [Asn1, Val5,Tyr9] angiotensin I (related to native angiotensin in snake, Elaphe climocophora (IV). Pressor properties of these peptides were compared with the peptides isolated from other species and related synthetic analogs in one representative species from three distinct classes of vertebrates: 1) elasmobranchs: spiny dogfish shark; 2) birds: domestic chicken; and 3) mammals: rat. The effect of angiotensins on short circuit current (to compare sodium and water permeability) was studied by adding these on the dermal side of the isolated frog skin. In the rat pressor bioassays, the above peptides possessed, respectively, I, 87.8%; II, 51.5%; III, 65.2%; and IV, 60.3% pressor activity of [Ile5] angiotensin II, which was blocked with a converting-enzyme inhibitor, captopril. In the conscious dogfish shark, the percentage increase of blood pressure based on preinjection level (= 100) in the dorsal aortic pressure was 35% to 60% for [Asp1,Ile5,His9] angiotensin I (human) (3 micrograms/kg), [Asp1,Val5,Ser9] angiotensin I (chicken) (3 micrograms/kg), [Asp1,Ile5] angiotensin II (3.6 micrograms/kg), and [Asn1,Val5] angiotensin II (6 micrograms/kg). Likewise, a 30% to 35% increase in blood pressure was obtained with angiotensin III (3 micrograms/kg), [Ile8] angiotensin II (4.4 micrograms/kg), and [Sar1,Ile8] angiotensin II (9.1 micrograms/kg). [Sar1,Thr8] angiotensin II and [Ile8] angiotensin I did not produce a significant pressor response even at high dose-level (8 micrograms/kg).(ABSTRACT TRUNCATED AT 250 WORDS)