Effects of combined renovascular hypertension and diabetes mellitus on myocardial cells, non-vascular interstitium and capillaries: a stereological study on rat hearts

Stereological study of the diabetic heart of male rats

The present study aimed to quantitatively compare the normal and diabetic hearts of rats using stereological methods. Diabetic and control rats received streptozotocin (60 mg/kg) and no treatments, respectively. On the 56^th day, the hearts were removed and their total volume was estimated using isotropic Cavalieri method. The total volume of the connective tissues and vessels, total length and diameter of the vessels, total number of cardiomyocytes nuclei, and the mean volume of the cardiomyocytes were estimated, as well. In comparison to the control animals, 60 and 43% increase was observed in the total volume of the connective tissue and microvessels of the diabetic rats, respectively (P<0.05). The percent of the vessel profiles with the diameter of 2-4 µm was decreased, while the percent of the vessel profiles with the diameter of 4.1-8 µm was increased in the diabetic hearts (P<0.05). No significant difference was found in the vessels with more than 8 µm diameters. The total number of the cardiomyocytes' nuclei and the number-weighted mean volume were respectively decreased by 37 and 64% in the diabetic group (P<0.01). A significant difference was observed between the two groups concerning the left ventricle volume to body weight ratio as an index for ventricular hypertrophy (P<0.05), while no difference was found regarding the right ventricle to body weight ratio. It can be concluded that diabetes can induce structural changes, including loss and/or atrophy of the cardiomyocytes, accompanied with increase in the connective tissue in the rats' hearts.

Simultaneous renal hypertension and type 2 diabetes exacerbate vascular endothelial dysfunction in rats

Despite the high rate of occurrence of both diabetes and hypertension in humans, the cardiovascular effects of the two conditions have not been investigated when they occur simultaneously. Thus this study examined the vascular effects of simultaneous type 2 diabetes and renal hypertension on endothelial function. Serum malondialdehyde and systolic blood pressure (SBP) were measured, glucose tolerance test (GTT) was performed, and concentration-response to phenylephrine (PE) in the absence and presence of nitro-l-arginine methyl ester (l-NAME), acetylcholine and sodium nitroprusside were conducted on aortic rings from diabetic control, type 2 diabetes, sham-operated, renal hypertensive, and simultaneous type 2 diabetes plus hypertension rats respectively. Hypertension, diabetes, and simultaneous diabetes and hypertension were associated with either increased or decreased maximal responses (E(max)) of PE dependent on in the presence or absence of l-NAME. There was also increased serum malondialdehyde and decreased E(max) of acetylcholine. Thus simultaneous hypertension and diabetes caused a greater decrease in E(max) of acetylcholine compared to that seen with either diabetes or hypertension alone higher than that seen in hypertension. The blood glucose during GTT was lower than that seen in diabetes groups. Thus simultaneous type 2 diabetes and the SBP was renal hypertension is associated with improved glucose tolerance, but with further deterioration of endothelial dysfunction compared with either condition alone.

Effects of transgenic endothelin-2 overexpression on diabetic cardiomyopathy in rats

BACKGROUND

Transgenic overexpression of human endothelin-2 in rats was used to characterize the contribution of endothelin to diabetic cardiomyopathy.

MATERIALS AND METHODS

Diabetes mellitus was induced by streptozotocin in transgenic rats and transgene-negative controls. Nondiabetic animals were included as well to form a 4-group study design. Heart morphological and molecular alterations were analysed following 6 months of hyperglycaemia.

RESULTS

Plasma endothelin concentrations were significantly higher in both transgenic groups than in wild-type groups (nondiabetic: 3.5 +/- 0.4 vs. 2.1 +/- 0.2, P < 0.05; diabetic: 4.5 +/- 0.4 vs. 2.5 +/- 0.4 fmol mL(-1), P < 0.01). Diabetes induced cardiac hypertrophy in both wild-type and transgenic rats and showed the highest myocardial interstitial tissue volume density in diabetic transgenic rats (1.5 +/- 0.07%) as compared with nondiabetic transgenic (1.1 +/- 0.03%), nondiabetic wild-type (0.8 +/- 0.01%) and diabetic wild-type rats (1.1 +/- 0.03%; P < 0.01 for all comparisons). A similar pattern with the most severe changes in the enothelin-2 transgenic, diabetic animals was observed for hypertrophy of the large coronary arteries and the small intramyocardial arterioles respectively. Cardiac mRNA expression of endothelin-1, endothelin receptors type A and B were altered in some degree by diabetes or transgenic overexpression of endothelin-2, but not in a uniform manner. Blood pressure did not differ between any of the four groups.

CONCLUSIONS

Overexpression of the human endothelin-2 gene in rats aggravates diabetic cardiomyopathy by more severe coronary and intramyocardial vessel hypertrophy and myocardial interstitial fibrosis. This transgenic intervention provides further and independent support for a detrimental, blood pressure-independent role of endothelins in diabetic cardiac changes.

Oxytalan elastic and collagen fibers during the repair process in experimental nitric oxide inhibition

PURPOSE

To evaluate the repair process in rats with experimentally induced arterial hypertension. This study aimed to evaluate lesions in the ventricular myocardium and the repair process during experimental hypertension induced by systemic blockage of nitric oxide using N-omega-nitro-L-arginine methyl ester hydrochloride (L-NAME). Nitric oxide is an endothelial vasorelaxing factor and is necessary for the maintenance of normal arterial pressure, and L-NAME is an analog and antagonist of L-arginine, the substrate of the nitric oxide synthase.

MATERIALS AND METHODS

We used 26 normotensive young male Wistar rats belonging to several litters. Animals were treated with oral administration of L-NAME dissolved in water (75 mg/100 mL) for 43 days. Hearts were weighed and processed by routine methods. Special stains utilized were Gomori's trichrome (aniline blue), picrosirius red polarization to identify fibrillar collagen, alcian blue technique (pH 0.5 and pH 2.5) to identify glycosaminoglycans, periodic acid-Schiff technique (with and without amylases) to identify proteoglycans, and Weigert's resorcinol fuchsin solution (with and without oxone) to identify elastic fibers.

RESULTS

The results showed significant elevation of the arterial pressure (P <0.01) and significant increase of cardiac weight (P <.0001) in the L-NAME (hypertensive) treated group, as compared to an untreated control group. The histological analysis demonstrated wide infarcted myocardial areas in animals with nitric oxide blockade; several vascular changes such as thickening of the muscular tunica with fibrosis; thickening in the wall of small arteries and arterioles; and fibrinoid necrosis in the wall to nearly complete luminal obliteration. Reparative fibrosis involved mainly oxytalan elastic and collagen fibers.

CONCLUSION

Oxytalan elastic and collagen fibers are of great importance for the postinfarct repair process occurring during experimental nitric oxide inhibition.

Postnatal growth of cardiomyocytes in the left ventricle of the rat

We studied the development of myocytes and interstitium using perfusion-fixed left ventricles obtained from normal female Wistar rats at 5 days (n = 5), 25 days (n = 5), and 125 days (n = 5) of age. Using design-based stereological methods and light microscopy, we estimated the following parameters: volume of left ventricle made up by myocytes, myocyte nuclei, and interstitium; total numbers of myocyte and non-myocyte nuclei; mean volumes of myocyte nuclei; the total volume, surface area, and length of fibers; and the mean star volumes of fibers. Some derived parameters were also calculated, namely, the mean myocardium volume per nucleus and the mean fiber cross-sectional area. We found that postnatal myocyte growth after day 5 in the young rat is largely hypertrophic, while interstitial growth is hyperplastic. The increase in left ventricular mass was 10-fold over the ages studied, whereas total length, surface area, and volume of fibers increased approximately 3-, 8-, and 11-fold over the period. Relative rates of growth implied that fiber growth was dominated by an increase in length compared to other dimensions. The total number of myocyte nuclei ( approximately 30 x 10(6)) did not change between 5 and 25 days of age, but then almost doubled in 125-day-old rats. The number of non-myocyte nuclei increased 9-fold over the period studied in an exponential manner. The mean myocyte nucleus volume tripled between the ages of 5 and 25 days and then remained the same. The volume-weighted mean nucleus volume was highly variable and showed no significant trend with age. Our results provide support for the claim made by some researchers that myocyte proliferation had ceased by day 5 after birth, but do not provide evidence for binucleation of myocytes between 5 and 25 days after birth. Reported numbers of myocyte nuclei express a net growth and do not rule out both myocyte death and creation throughout the early postnatal period. We clearly detect an increase in the number of myocyte nuclei from 25 to 125 days but are not able to state whether this increase reflects myocyte proliferation or myocyte binucleation. To determine this would require special double-staining techniques to delineate intercalated discs and myocyte membranes. Our results agree very well with the limited data available from other studies that have used unbiased stereology. It is important to use unbiased designs that consider anisotropy as well as heterogeneity of the heart in sampling schemes, and to determine absolute quantities to avoid problems associated with interpreting changes in density (the "reference trap").

Myocyte loss in early left ventricular hypertrophy of experimental renovascular hypertension

Left ventricular hypertrophy (LVH) develops very early in experimental renovascular hypertension after clipping of one renal artery and is accompanied by a remodeling of cardiac structure which has not yet been investigated in detail. It was the aim of the present study to analyze changes in cardiomyocyte number and volume in LVH after 2 weeks of renovascular hypertension. Sprague-Dawley rats were subjected to clipping of the left renal artery (2K1C) or sham operation (sham). One group of 2K1C rats received antihypertensive treatment with dihydralazine. The experiment was terminated after 2 weeks. Hearts were investigated using stereological methods, electron microscopy, immunohistology for the proliferation marker proliferating cell nuclear antigen, the pro- and anti-apoptotic proteins Bax and Bcl-2 as well as the TUNEL technique. After 2 weeks, systolic blood pressure and relative left ventricular weight were significantly higher in untreated 2K1C animals than in sham and dihydralazine-treated 2K1C rats. Volume fraction of interstitial tissue and capillary length density were not different, whereas wall thickness of intramyocardial arteries was significantly higher in untreated 2K1C (5.12+/-0.7 micro m) than in sham (3.92+/-0.6 micro m) and in dihydralazine-treated 2K1C (3.91+/-0.7 micro m) rats. Cardiomyocyte diameter and volume were significantly higher in untreated 2K1C than in sham animals. The number of cardiomyocytes per left ventricle was significantly lower in untreated 2K1C rats (5.5+/-1.6 vs 3.9+/-6.9 x10(7)). Using immunohistochemistry, no direct evidence of apoptosis was found, but a relative higher expression of the anti-apoptotic protein bcl-2 expression was seen in untreated 2K1C than in sham animals. This may reflect a protective mechanism as a consequence of earlier occurring apoptosis. These observations document that experimental renovascular hypertension induces a rapidly developing LVH characterized by marked cardiac remodeling and substantial loss of cadiomyocytes.

A comparison of ultrastructural changes on endomyocardial biopsy specimens obtained from patients with diabetes mellitus with and without hypertension

The pathogenesis of diabetic cardiomyopathy is unknown. The synergistic, or enhanced, effect of hypertension on pathological changes in the heart of diabetic patients has been highly suspected. The purpose of this study was to evaluate the myocardial changes related to diabetes mellitus with and without hypertension, using biopsy specimens. We examined the ultrastructural changes in biopsy specimens of the endomyocardium obtained from 25 patients. They were divided into four groups: controls without hypertension or diabetes mellitus (n = 6), and patient with hypertension (n = 3), diabetes mellitus (n = 8), and diabetes with hypertension (n = 8). The diabetic patients showed nearly normal or mildly depressed systolic left ventricular function. Ultrastructural pictures were analyzed for thickening of the capillary basement membrane, presence of toluidine blue-positive materials (i.e., materials showing metachromasia) in the myocytes, size of myocytes, and interstitial fibrosis. The thickening of the capillary basement membrane, the accumulation of toluidine blue-positive materials, and interstitial fibrosis were all significantly greater in the patients with diabetes mellitus compared to the control subjects. The myocytes tended to be small (cell atrophy) in the diabetes group. Although these pathological changes in the heart were characteristic of diabetic patients, irrespective of the presence or absence of hypertension, the presence of hypertension increased the pathological changes of myocardial cells as well as abnormality in the capillary vessels in patients with diabetes mellitus. Alterations in the myocardial cells and capillaries, caused by diabetes mellitus, may lead to myocardial cell injury and interstitial fibrosis and, ultimately, to ventricular systolic and diastolic dysfunction, especially when the diabetes is accompanied by hypertension.

Reduced capillary density in the myocardium of uremic rats--a stereological study

Using stereological techniques capillaries, interstitium and myocardial fibers were analyzed in perfusion-fixed hearts of subtotally nephrectomized male Sprague-Dawley rats with uremia of 14 months duration (or their sham-operated controls). Uremic rats had higher systolic blood pressure (140 +/- 20.3 mm Hg vs. 119 +/- 6.61 mm Hg) and left ventricular weight/body weight ratio (3.37 +/- 0.09 mg/kg vs. 2.01 +/- 0.12 mg/kg) than controls, and had slight anemia (Hct 35.0 +/- 3.16% vs. 40.4 +/- 3.3%). Length density (Lv) of capillaries, that is, capillary length per unit myocardial volume, was significantly (P < 0.001) decreased in uremia (2485 +/- 264 mm/mm3 vs. 3329 +/- 194 mm/mm3) versus controls. In parallel, surface density and volume density of the capillary lumina were also reduced (7.95 +/- 1.69 cm3/cm3 vs. 11.4 +/- 1.8 cm3/cm3) in the uremic rats. We conclude that in experimental uremia, cardiac hypertrophy is not accompanied by a commensurate increase in capillaries.