Ultrastructure and histochemistry of rat myocardial capillary endothelial cells in response to diabetes and hypertension

Insufficient growth and rarefaction of capillaries, followed by endothelial dysfunction may represent one of the mostcritical mechanisms involved in heart damage. In this study we examined histochemical and ultrastructural changes inmyocardial capillary endothelium in two models of heart failure streptozotocin-induced diabetes mellitus (STZ) and NO-deficient hypertension in male Wistar rats. Diabetes was induced by a single i.v. dose of STZ (45 mg/kg) and chronic 9-week stage was analysed. To induce NO-deficient hypertension, animals were treated with inhibitor of NO synthase L-nitroarginine methylester (L-NAME) (40 mg/kg) for 4 weeks. Left ventricular tissue was processed for enzyme cata-lytic histochemistry of capillary alkaline phosphatase (AlPh), dipeptidyl peptidase IV (DPP IV), and endothelial NOsynthase/NADPH-diaphorase (NOS) and for ultrastructural analysis. In diabetic and hypertensive rats, lower/absentAlPh and DPP IV activities were found in focal micro-areas. NOS activity was significantly reduced and persisted onlylocally. Quantitative evaluation demonstrated reduction of reaction product intensity of AlPh, DPP and NOS by 49.50%,74.36%, 20.05% in diabetic and 62.93%, 82.71%, 37.65% in hypertensive rats. Subcellular alterations of endothelialcells were found in heart of both groups suggesting injury of capillary function as well as compensatory processes.Endothelial injury was more significant in diabetic animals, in contrast the adaptation was more evident in hypertensiveones. Concluding: both STZ-induced diabetes- and NO-deficient hypertension-related cardiomyopathy were accompa-nied by similar features of structural remodelling of cardiac capillary network manifested as angiogenesis and angiopathy.The latter was however, predominant and may accelerate disappearance of capillary endothelium contributing to myo-cardial dysfunction.