Comparison of the cardiovascular and neural activity of endothelin-1, −2, −3 and respective proendothelins: effects of phosphoramidon and thiorphan

Authors

  • Giovan G. Mattera,

    Corresponding author
    1. Pharmacology Department, Laboratori Guidotti SpA, Via Livornese 402, San Piero a Grado, 56122, Pisa, Italy
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  • Anthony Eglezos,

    1. Pharmacology Department, Laboratori Guidotti SpA, Via Livornese 402, San Piero a Grado, 56122, Pisa, Italy
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  • Anna Rita Renzetti,

    1. Pharmacology Department, Laboratori Guidotti SpA, Via Livornese 402, San Piero a Grado, 56122, Pisa, Italy
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  • Jacques Mizrahi

    1. Pharmacology Department, Laboratori Guidotti SpA, Via Livornese 402, San Piero a Grado, 56122, Pisa, Italy
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    • Italfarmaco, S.p.A., Via dei Lavoratori, 54 20092 Cinisello Balsamo, Milano, Italy.


Pharmacology Department, Laboratori Guidotti SpA, Via Livornese 402, San Piero a Grado, 56122, Pisa, Italy

Abstract

  • 1In the anaesthetized, ganglion-blocked rat, intravenous boluses of endothelin-1, endothelin-2 and endothelin-3 induced a transient hypotensive effect followed by a potent long lasting pressor response (ED50 mmHg: 0.72 ± 0.05, 1.8 ± 0.2 and 2.7 ± 0.3 nmol kg−1, respectively). The maximal effect for the three peptides was of a similar order of magnitude (ΔMAP: 84 to 89 mmHg). Neither of these effects was influenced by phosphoramidon or thiorphan (10 mg kg−1, i.v.).
  • 2Intravenously administered big-endothelin-1 and −2 induced a transient (1–2 min) hypotension followed by a potent long lasting (> 25 min) vasopressor effect (ED50 mmHg: 1.8 ± 0.2 and 6.7 ± 0.4 nmol kg−1, respectively), with a similar maximal activity (Δ MAP: 85 ± 4 and 81 ± 2.4 mmHg, respectively). The onset of the big-endothelin-1 vasopressor effect was more rapid (5–6 min) than that of big-endothelin-2 (10–13 min). Big-endothelin-3 was found to induce only a potent, long lasting (> 35 min) hypertension, with a maximal effect of 75 ± 4.6 mmHg at 10 nmol kg−1 and an ED50 mmHg of 6.5 ± 0.4 nmol kg−1. The onset of this effect was much slower (20–25 min) than that of the other proendothelins. Pressor responses induced by big-endothelin-1, −2 and −3 (3, 15 and 10 nmol kg−1, respectively) were markedly reduced (60, 80 and 100%) in the presence of phosphoramidon (10 mg kg−1, i.v.). Thiorphan (10 mg kg−1, i.v.) did not inhibit the effects of big-endothelin-1, −2 and −3.
  • 3In the electrically stimulated rat vas deferens, endothelin-1 and −2 were found to be equipotent enhancers of the twitch response (EC100%: 4.0 ± 0.4 nm and 7.9 ± 4.8 nm, respectively), both about 3–4 fold as active as endothelin-3 (EC100%: 19 ± 2.5 nm). Endothelin-1 and −3 showed a comparable maximal stimulatory effect (Emax: 296 ± 30 and 262 ± 24%) while endothelin-2 was less active (Emax: 194 ± 30%).
  • 4Big-endothelin-1 and −2 were potent enhancers of the twitch reponse too (EC100%: 10.0 ± 2.6 nm and 21.6 ± 3.2 nm, respectively), with a comparable maximal stimulatory effect (Emax: 254 ± 22 and 264 ± 24%). Big-endothelin-3 was found to be less potent (EC100%: 275 ± 21 nm), but retained a marked potentiating effect (Emax: 200 ± 38%). Phosphoramidon, but not thiorphan, concentration-dependently (10 and 100 μm) reduced big-endothelin-1 (58 and 86% respectively) and big-endothelin-2 (21 and 56%)-mediated responses. Conversely, the big-endothelin-3 effect was reduced by phosphoramidon only at 100 μm (−70%), while thiorphan acts concentration-dependently (31 and 71% at 10 and 100 μm respectively); thus, in the rat vas deferens, big-endothelin-1 and −2 were as potent as their corresponding endothelins, while big-endothelin-3 was about 20 times less potent than endothelin-3.
  • 5The increasing effect of endothelin-2 (194 ± 30% over baseline) was significantly enhanced by either 10 μm phosphoramidon (277 ± 42%) or thiorphan (318 ± 15%). The endothelin-1 and endothelin-3-mediated twitch enhancement was not affected by the two protease inhibitors (10 μm).
  • 6These results suggest that in vivo big-endothelin-1, −2 and −3, are processed through a similar phosphoramidon-sensitive enzymatic pathway although with different apparent affinity. This enzymatic process is probably attributable to a neutral endoprotease, distinct from neutral-endopeptidase 24.11 (NEP). On the other hand, a NEP-like enzymatic activity may be involved, in the rat vas deferens, in the activation of big-endothelin-3 to endothelin-3 and in the metabolism of endothelin-2, but not of endothelin-1 or endothelin-3.

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