Conversion of big endothelin-1 in rat uterus causes contraction mediated by ETA receptors.
Like endothelin-1 (ET-1), its immediate human precursor big ET-1 (1-100 nM) increased the rate of spontaneous phasic contractions and caused graded tonic contractions of isolated rat uterus strips. The tonic contraction to big ET-1 (10 nM) was markedly blocked by phosphoramidon (100 microM), which did not modify the response to an equipotent concentration of ET-1 (3 nM). Responses to big-ET-1 (30 nM) were abolished in calcium-free medium, but those to ET-1 (10 nM) were only reduced by this condition. The EC50 of big ET-1 for inducing tonic contraction was only sevenfold greater than that of ET-1, and both peptides produced a maximal response similar to that evoked by KCl 80 mM. ET-3 was much less potent. The selective ETA receptor antagonist BQ-123 (40-600 nM) caused graded rightward shifts of the ET-1 curve without affecting the maximal response, yielding a Schild plot with a slope not different from unity and a pA2 value of 7.76. BQ-123 (100 nM) did not affect contractions induced by oxytocin (5 nM), acetylcholine (3 microM), or bradykinin (0.3 nM), but inhibited responses to both big ET-1 and ET-1. Therefore, the rat uterus contains a phosphoramidon-sensitive, calcium-dependent endothelin-converting enzyme that readily converts big ET-1 into ET-1, which then contracts the myometrium via activation of ETA receptors.
Rae
G A
GA
Department of Pharmacology, Universidade Federal de Santa Catarina, Florianopolis, Brazil.
Calixto
J B
JB
D'Orléans-Juste
P
P
D000595:Amino Acid Sequence; D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000037:antagonists & inhibitors / Q000378:metabolism; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1; D000072396:Endothelin-Converting Enzymes; D016232:Endothelins / Q000378:metabolism*; D005260:Female; D006020:Glycopeptides / Q000494:pharmacology; D066298:In Vitro Techniques; D008666:Metalloendopeptidases; D008969:Molecular Sequence Data; D010456:Peptides, Cyclic / Q000494:pharmacology; D011498:Protein Precursors / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D017466:Receptors, Endothelin / Q000187:drug effects / Q000502:physiology*; D014590:Uterine Contraction / Q000502:physiology*; D014599:Uterus / Q000201:enzymology / Q000378:metabolism*
D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1; D016232:Endothelins; D006020:Glycopeptides; D010456:Peptides, Cyclic; D011498:Protein Precursors; D017466:Receptors, Endothelin; D016282:Aspartic Acid Endopeptidases; D008666:Metalloendopeptidases; D000072396:Endothelin-Converting Enzymes; C072247:cyclo(Trp-Asp-Pro-Val-Leu); C008890:phosphoramidon