Aims/hypothesis. There is little information whether cardiac capillary supply is deranged in diabetes. Hyperglycaemia is a potent stimulus for endothelin-1 (ET-1) production. We therefore hypothesised that increased ET-1 production in Streptozotocin-induced Type 1 diabetes causes abnormalities of cardiac capillaries and the aorta. To this end we compared the effects of an ET receptor A blocker (ET A -RB) with that of an ACE-inhibitor (ACE-i) or their combination in rats with Streptozotocin (STZ) diabetes. Methods. Sprague Dawley rats were injected with 65 mg STZ i.v. and subsequently developed diabetes. Rats were left untreated or received daily either the ACE-i Trandolapril, the ET A -RB Darusentan or a combination of both. After 6 months the experiment was terminated and the heart and the aorta were investigated using quantitative morphological techniques. Results. ACE-i but not ET A -RB lowered blood pressure in STZ Type 1 diabetic rats. Capillary length density was lower in untreated STZ diabetic rats (2932±128 mm/mm 3 ) compared to non-diabetic control rats (3410±252 mm/mm 3 ). Treatment with ACE-i (3568±431 mm/mm 3 ), but not with ET A -RB (2893±192 mm/mm 3 ), prevented the decrease in capillary supply. Volume density of the myocardial interstitium was higher in untreated STZ diabetic rats (0.86±0.04%) compared to non-diabetic control rats (0.36±0.06%). In all three intervention groups the values were lower (ACE-i: 0.53±0.05%, ET A -RB: 0.7±0.08% and combination: 0.69±0.1). Conclusion/interpretation. Our study identifies a capillary defect of the heart in STZ diabetes, i.e. decreased capillary supply. This abnormality was reversed by ACE-i, but not by ET A -R blockade. A similar trend, although not complete normalisation, was seen in cardiac fibrosis. [Diabetologia (2004) 47:316-324]

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