Conversion of big ET-1 in the rat lung: role of phosphoramidon-sensitive endothelin-1-converting enzyme.
We examined conversion of Big endothelin-1 (ET-1) to mature ET-1 and pressor action during perfusion of the isolated perfused rat lung with Big ET-1. Big ET-1 caused a concentration-related increase in perfusion pressure and the pressor molar potency of the peptide was fivefold less than that of ET-1. Pressor responses to Big ET-1 were accompanied by an increase in immunoreactive-ET (IR-ET) levels in the perfusate and in the lung tissues. Pretreatment with phosphoramidon (10(-4) M), a metalloproteinase inhibitor, markedly suppressed the pressor action and increment in IR-ET in the tissues. Unexpectedly, the amount of IR-ET in the perfusate during perfusion of Big ET-1 was not influenced by phosphoramidon treatment. On the other hand, chymostatin, an inhibitor of chymotrypsin-like enzymes, effectively suppressed IR-ET levels in the perfusate; however, this enzyme inhibitor was without effect on the pressor action of Big ET-1 or on the increase in IR-ET levels in lung tissues. We tentatively conclude that the phosphoramidon-sensitive conversion of Big ET-T to ET-1 is linked to the pressor action of Big ET-1 in the isolated perfused rat lung. In addition, it seems likely that chymostatin-sensitive conversion of Big ET-1 to ET-1 does not play a major role in the conversion of the precursor to the mature form. We propose that IR-ET present in the tissues rather than that in the perfusate is a better indicator of the functional conversion of Big ET-1 in the rat lung.
Hisaki
K
K
Department of Pharmacology, Osaka University of Pharmaceutical Sciences, Japan.
Matsumura
Y
Y
Maekawa
H
H
Fujita
K
K
Takaoka
M
M
Morimoto
S
S
D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000378:metabolism*; D002918:Chymotrypsin / Q000037:antagonists & inhibitors; D004305:Dose-Response Relationship, Drug; D019332:Endothelin-1; D000072396:Endothelin-Converting Enzymes; D016232:Endothelins / Q000378:metabolism* / Q000494:pharmacology*; D006020:Glycopeptides / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D008168:Lung / Q000187:drug effects / Q000201:enzymology / Q000502:physiology*; D008297:Male; D008666:Metalloendopeptidases / Q000037:antagonists & inhibitors*; D009842:Oligopeptides / Q000494:pharmacology; D010477:Perfusion; D011498:Protein Precursors / Q000378:metabolism; D011652:Pulmonary Circulation / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D019332:Endothelin-1; D016232:Endothelins; D006020:Glycopeptides; D009842:Oligopeptides; D011498:Protein Precursors; C002101:chymostatin; D002918:Chymotrypsin; D016282:Aspartic Acid Endopeptidases; D008666:Metalloendopeptidases; D000072396:Endothelin-Converting Enzymes; C008890:phosphoramidon