Raised blood pressure, not renin-angiotensin systems, causes cardiac fibrosis in TGR m(Ren2)27 rats.
OBJECTIVE
Elevated systemic arterial blood pressure is associated with left ventricular hypertrophy and fibrosis. It has been suggested that both circulating and local myocardial renin-angiotensin systems play a role in mediating these responses. Here we describe the natural history of ventricular hypertrophy and fibrosis in the transgenic (mRen2)27 rat--a monogenetic model--which has a high tissue expression of the murine renin transgene, and suffers severe hypertension. We further explored the relative contribution of both hypertensive burden and circulating and tissue renin-angiotensin systems to the fibrotic process.


METHODS
The transgenic rats were treated from 28 days old with (1) a hypotensive dose of the ACE inhibitor ramipril which inhibited both tissue and circulating ACE activity, (2) the calcium antagonist amlodipine, or (3) a non-hypotensive dose of ramipril which inhibited about 60% of tissue ACE activity with little effect on circulating ACE. Normotensive Sprague-Dawley rats were used as controls.


RESULTS
The transgenics developed left ventricular hypertrophy along with perivascular and interstitial fibrosis which became progressively worse up to 24 weeks of age. Both the high dose of ramipril and amlodipine prevented the hypertrophy and fibrosis, whereas tissue ACE inhibition without lowering blood pressure had no effect, and actually led to a worsening of the fibrosis by 24 weeks.


CONCLUSIONS
These results suggest that the development of left ventricular hypertrophy and fibrosis in the transgenic (mRen2)27 rat are regulated by blood pressure and not activity of the renin-angiotensin systems and that progression of fibrosis at 24 weeks involves a mechanism unrelated to local renin-angiotensin activity.
Bishop
J E
JE
Centre for Cardiopulmonary Biochemistry and Respiratory Medicine, University College London Medical School, Rayne Institute, 5 University Street, WC1E 6JJ, London, UK.
Kiernan
L A
LA
Montgomery
H E
HE
Gohlke
P
P
McEwan
J R
JR
D017311:Amlodipine / Q000627:therapeutic use; D000806:Angiotensin-Converting Enzyme Inhibitors / Q000627:therapeutic use; D000818:Animals; D030801:Animals, Genetically Modified; D000959:Antihypertensive Agents / Q000627:therapeutic use; D003094:Collagen / Q000032:analysis; D005355:Fibrosis; D006973:Hypertension / Q000150:complications* / Q000378:metabolism / Q000473:pathology; D017379:Hypertrophy, Left Ventricular / Q000209:etiology / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D009206:Myocardium / Q000737:chemistry / Q000473:pathology*; D007703:Peptidyl-Dipeptidase A / Q000097:blood; D017257:Ramipril / Q000627:therapeutic use; D051381:Rats; D017207:Rats, Sprague-Dawley; D012084:Renin-Angiotensin System; D013997:Time Factors
D000806:Angiotensin-Converting Enzyme Inhibitors; D000959:Antihypertensive Agents; D017311:Amlodipine; D003094:Collagen; D007703:Peptidyl-Dipeptidase A; D017257:Ramipril