Radioimmunoassay evidence that the pressor effect of big endothelin-1 is due to local conversion to endothelin-1.
Compared with endothelin-1 (ET-1), big endothelin-1 (big ET-1) is only weakly active on isolated vascular smooth muscle preparations. However, on systemic administration high doses of big ET-1 (1 nmol.kg-1) are approximately equipotent to ET-1, indicating the existence of an endothelin converting enzyme in the circulation that rapidly converts big ET-1 to ET-1. In this study arterial blood levels of big ET-1 and ET-1 immunoreactivity were measured after bolus i.v. administration of big ET-1 (1 or 3 nmol.kg-1) or ET-1 (1 nmol.kg-1) in anaesthetised male Wistar rats. In addition, the effect of phosphoramidon (10 mg.kg-1) on the pressor response to big ET-1 and its disappearance rate from the circulation were examined. After big ET-1 injection, circulating ET-1 concentrations did not exceed 2% of the big ET-1 level. Phosphoramidon reduced the pressor response to big ET-1 by 93%, but did not alter its rate of clearance from the circulation. Thus exogenous big ET-1 is converted locally in the vasculature and its disappearance from the circulation is not dependent on conversion to ET-1.
William Harvey Research Institute, Medical College of St Bartholomew's Hospital, London, U.K.
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D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D019332:Endothelin-1; D016232:Endothelins / Q000097:blood* / Q000493:pharmacokinetics / Q000494:pharmacology*; D006020:Glycopeptides / Q000494:pharmacology; D008297:Male; D011498:Protein Precursors / Q000097:blood* / Q000493:pharmacokinetics / Q000494:pharmacology*; D011863:Radioimmunoassay; D051381:Rats; D017208:Rats, Wistar
D019332:Endothelin-1; D016232:Endothelins; D006020:Glycopeptides; D011498:Protein Precursors; C008890:phosphoramidon