Cardiac chymase converts rat proAngiotensin-12 (PA12) to angiotensin II: effects of PA12 upon cardiac haemodynamics.
OBJECTIVE
The aim of this study was to observe the direct physiological and biochemical cardiac effects in response to a newly identified putative component of the renin-angiotensin system, proangiotensin-12 (PA12); and investigate whether PA12 can serve as a substrate for Angiotensin II (AngII) generation.


RESULTS
The direct cardiac actions of PA12 and its role as a substrate for chymase-dependent AngII generation were investigated in Sprague-Dawley rats using an isolated heart model of cardiac ischaemia-reperfusion injury. PA12 potently constricted coronary arteries with no significant effect on left-ventricular contractility. PA12 impaired recovery from global ischaemia, maintaining coronary constriction and markedly increasing release of creatine kinase and troponin I (TnI), indicating greater myocardial injury. Analysis of perfusate collected after transcardiac passage revealed a marked increase in AngII production from hearts infused with PA12. Cardiac AngII production was not blocked by angiotensin-converting enzyme inhibitors, whereas inhibition of chymase with chymostatin significantly reduced AngII production and attenuated PA12-induced vasoconstriction and myocardial damage following ischaemia. Furthermore, Angiotensin II type 1 receptor (AT(1)R) blockade abolished PA12 activity. In vitro, PA12 was efficiently and precisely converted to AngII as assessed on reverse phase-high performance liquid chromatography coupled to tandem mass spectrometry. This conversion was blocked by chymostatin.


CONCLUSIONS
PA12 may act as a circulating substrate for cardiac chymase-mediated AngII production, in contrast to ACE-mediated AngII production from AngI.
Prosser
Hamish C G
HC
School of Biological Sciences, University of Canterbury, PO Box 4800, Christchurch, New Zealand. hamishprosser@gmail.com
Forster
Malcolm E
ME
Richards
A Mark
AM
Pemberton
Chris J
CJ
D000804:Angiotensin II / Q000378:metabolism*; D047228:Angiotensin II Type 1 Receptor Blockers / Q000494:pharmacology; D000806:Angiotensin-Converting Enzyme Inhibitors / Q000494:pharmacology; D000808:Angiotensinogen / Q000378:metabolism*; D000818:Animals; D009320:Atrial Natriuretic Factor / Q000378:metabolism; D015415:Biomarkers / Q000378:metabolism; D001794:Blood Pressure; D002851:Chromatography, High Pressure Liquid; D053818:Chymases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003331:Coronary Vessels / Q000378:metabolism / Q000503:physiopathology; D003402:Creatine Kinase / Q000378:metabolism; D006439:Hemodynamics / Q000187:drug effects; D008297:Male; D009200:Myocardial Contraction; D015428:Myocardial Reperfusion Injury / Q000201:enzymology* / Q000473:pathology / Q000503:physiopathology; D009206:Myocardium / Q000201:enzymology* / Q000473:pathology; D009842:Oligopeptides / Q000494:pharmacology; D010446:Peptide Fragments / Q000378:metabolism*; D010477:Perfusion; D051381:Rats; D017207:Rats, Sprague-Dawley; D012084:Renin-Angiotensin System / Q000187:drug effects; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D053719:Tandem Mass Spectrometry; D013997:Time Factors; D019210:Troponin I / Q000378:metabolism; D014661:Vasoconstriction; D016277:Ventricular Function, Left
D047228:Angiotensin II Type 1 Receptor Blockers; D000806:Angiotensin-Converting Enzyme Inhibitors; D015415:Biomarkers; D009842:Oligopeptides; D010446:Peptide Fragments; D015842:Serine Proteinase Inhibitors; D019210:Troponin I; C515557:proangiotensin-12, rat; D000808:Angiotensinogen; D000804:Angiotensin II; D009320:Atrial Natriuretic Factor; C002101:chymostatin; D003402:Creatine Kinase; D053818:Chymases