Virchows Archiv A Pathol Anat (1992) 420:499-506 VirchowsArch&A PathologicalAnatomy and Histopathology 9 Springer-Verlag 1992 Effects of combined renovascular hypertension and diabetes mellitus on myocardial cells, non-vascular interstitium and capillaries: a stereological study on rat hearts Marc Fischer 1, Gabriele Wiest 1, Ismail Tekesin 1, Kerstin Amann 1, Johannes Mann 2, Christian Hasslacher 2, Harald Derks~, and Gerhard Mall 1 Departments of ~ Pathology, 2 Internal Medicine, University of Heidelberg, W-6900 Heidelberg, Federal Republic of Germany Received June 30, 1991 / Received after revision September 4, 1991 / Accepted September 5, 1991 Summary. The effects of combined renovascular hyper- tension and diabetes mellitus on the rat heart were inves- tigated in order to detect possible synergistic effects of the two conditions. Hypertensive diabetic and hyperten- sive non-diabetic animals were compared to diabetic and non-diabetic controls. Hypertension was established for 12 weeks by a surgical stenosis of the left renal artery; diabetes mellitus was maintained for 8 weeks by a single intraperitoneal injection of 60 mg/kg streptozotocin. Light microscopic stereology did not reveal significant divergences between diabetic hypertensives and non-dia- betic hypertensives. Hypertension induced a focal peri- vascular and interstitial fibrosis with increased volume densities of non-vascular interstitium and fibrosis (P< 0.001). Capillary density (QA) was decreased in trans- verse sections (P<0.01) and increased in longitudinal sections (P<0.01). This indicates a three-dimensional remodelling of the capillary bed with an increased number of obliquely running capillaries. At least the length density (Lv) of capillaries (mm/mm 3) tends to be normalized in long-term renovascular hypertension. At the ultrastructural level, a synergism of hypertension and diabetes mellitus was observed: the volume ratio of mitochondria to myofibrils was significantly de- creased in hypertensive diabetics, but not in non-diabetic hypertensives or in diabetics. This may enhance the risk of cardiac deterioration. We conclude that the primary target of the synergistic damage in hypertensive diabetic heart muscle disease is the myocardial cell and not the cardiac interstitium. * Preliminary results of this study have been published in: Mall G (1991) Morphometric study on the rat heart in combined reno- vascular hypertension and diabetes mellitus. In : Nagano N, Dhalla NS (eds) The diabetic heart. Raven Press, New York, pp 115-124 ** Dedicated to Prof. Dr. med. G. Seifert on the occasion of his 70th birthday Offprint requests to: G. Mall, Pathologisches Institut, St/idtische Kliniken, Grafenstraf3e 9, W-6100 Darmstadt, Federal Republic of Germany Key words: Diabetes mellitus - Renovascular hyperten- sion - Myocardium - Stereology - Ultrastructure Introduction Hypertension and diabetes mellitus are frequent dis- orders in modern industrial countries. Epidemiological studies have established both conditions as risk factors of congestive failure even in the absence of coronary atherosclerosis (McKee et al. 1971: Kannel et al. 1974; Factor et al. 1980). Recently, co-existence of diabetes mellitus has been suggested to potentiate myocardial alterations and a spe- cific hypertensive diabetic heart muscle disease has been described (Fein et al. 1989) on the basis of autopsy stud- ies (Factor et al. 1980) and experimental investigations (Factor et al. 1981 ; Fein et al. 1984). It has been reported that one histological hallmark of the synergistic effects on the heart is the enhancement of cardiac fibrosis. However, this has never been established with objec- tive quantitative morphological methods. Furthermore, a recent experiment on short-term combination of hy- pertension and diabetes with quantitative methods did not reveal synergistic effects on the cardiac interstitium. At the ultrastructural level, however, synergistic damage of myocardial cells was observed (Mall et al. 1987a). The present experiment was designed in order to estab- lish possible long-term synergistic effects on cardiac structure, including myocardial cells and interstitial space. Materials and methods For this experiment 93 young male Wistar rats were primarily di- vided into two groups by the use of random numbers (see below). Sixty-six animals were treated with a surgical stenosis of the left renal artery with a silver clip of 0.217>0.22 mm internal diameter. Twenty-seven animals served as sham-operated control. After in- duction of hypertension, a 2% NaC1 solution was offered in order to prevent malignant hypertension (M6hring et al. 1976).