Synergistic effects of diabetes mellitus and renovascular hypertension on the rat heart--stereological investigations on papillary muscles

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.

Chronic type 1 diabetes in spontaneously hypertensive rats leads to exacerbated cardiac fibrosis

INTRODUCTION

Diabetes in human subjects is often associated with hypertension. The aim of this study was to examine the development of cardiac fibrosis following induction of type 1 diabetes in genetically hypertensive rats.

METHODS

Diabetes was induced by streptozotocin (STZ) injection in 8-week-old normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs) for a duration of 16 or 24 weeks. Aged-matched, nondiabetic WKY and SHRs were used as controls. At termination of treatment, the rats were anaesthetized, hearts arrested in diastole and perfusion fixed. A comprehensive examination of cardiac fibrosis throughout the right and left ventricles was undertaken in picrosirius red-stained sections, using image analysis and by undertaking collagen type I and type III immunohistochemistry.

RESULTS

Induction of diabetes in the SHRs led to a marked increase in the levels of interstitial fibrosis in the left ventricle plus septum (LV+S) at both 16 and 24 weeks duration (59% and 43% increase, respectively) and also in the right ventricle after 24 weeks duration of diabetes (35% increase compared to the nondiabetic SHR). Exacerbated perivascular fibrosis was also observed in the LV+S in the diabetic-hypertensive rats at the later time point. These effects of induction of diabetes were not observed in the normotensive strain.

CONCLUSIONS/INTERPRETATION

Our findings clearly demonstrate elevations in cardiac fibrosis when type 1 diabetes is combined with hypertension. Our findings thus stress the importance of closely monitoring both blood pressure and glucose levels in type 1 diabetic patients in order to prevent myocardial collagen deposition.

Capillary surface area is reduced and tissue thickness from capillaries to myocytes is increased in the left ventricle of streptozotocin-diabetic rats

The left ventricles of normal and diabetic rats, fixed by vascular perfusion were examined using modern stereological techniques to quantify changes in the morphology accompanying streptozotocin-induced diabetes. The heart weight to body weight ratio increased in diabetic rats whilst left ventricular volume remained unchanged. Papillary muscles from the diabetic animals showed prolonged time to peak tension and relaxation, and altered sensitivity to adrenalin and calcium. The apparent cardiomyopathy observed when body weight loss exceeds heart weight loss in experimental diabetes was accompanied by specific pathological changes in the composition of the left ventricle. In the diabetic animals the volume of extracellular components increased threefold and the volume of capillaries fell. The surface density and total surface area of capillaries was reduced, and oxygen diffusion distance to myocyte mitochondria increased. The volume fraction of myocyte mitochondria was reduced during streptozotocin-induced diabetes.

Diabetic cardiomyopathy

Diabetic cardiomyopathy as a distinct entity was first recognized by Rubler et al. in diabetics with congestive heart failure (CHF), who had no evidence of coronary atherosclerosis. The Framingham study showed a 2.4-fold increased incidence of CHF in diabetic men and a 5.1-fold increase in diabetic women over 18 years. Pathological studies show left ventricular hypertrophy and fibrosis with varying degrees of small vessel disease, the functional significance of which is uncertain. Hypertension was recognized as an important cofactor in the development of fatal congestive heart failure in diabetics. On cardiac catheterization, in patients symptomatic of heart failure, either congestive or restrictive patterns have been observed. In contrast, asymptomatic diabetics had decreased left ventricular compliance but normal systolic function on hemodynamic study. Noninvasive studies show alterations in systolic and especially diastolic function, particularly in diabetics with microvascular complications and/or coexistent hypertension. Using load-independent measures of contractility, however, systolic function was generally found to be normal in asymptomatic normotensive diabetics. Experimental studies have focused on the mildly diabetic dog and the severely diabetic rat. Decreased left ventricular compliance and increased interstitial connective tissue were observed in chronically diabetic dogs. In contrast, ventricular myocardium from diabetic rats exhibits a reversible decrease in the speed of contraction, prolongation of contraction, and a delay in relaxation. These mechanical changes are associated with a decreased myosin ATPase, a shift in myosin isoenzyme distribution, alterations in a variety of Ca2+ fluxes, and changes in responses to alpha- and beta-adrenergic and cholinergic stimulation. These biochemical changes may be secondary to alterations in carbohydrate, lipid, and adenine nucleotide metabolism in the diabetic heart.(ABSTRACT TRUNCATED AT 250 WORDS)

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

The effects of combined renovascular hypertension and diabetes mellitus on the rat heart were investigated in order to detect possible synergistic effects of the two conditions. Hypertensive diabetic and hypertensive 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-diabetic hypertensives. Hypertension induced a focal perivascular and interstitial fibrosis with increased volume densities of non-vascular interstitium and fibrosis (P less than 0.001). Capillary density (QA) was decreased in transverse sections (P less than 0.01) and increased in longitudinal sections (P less than 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/mm3) 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 decreased 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.

Effect of ageing and malnutrition on rat myocardium. I. The myocyte

The effects of ageing and starvation on the rat myocardium were studied by morphometric methods. Since cardiac muscle is a tissue with a high level of anisotropy, methods based on the concept of vertical planes were used to describe quantitative alterations in the rat myocyte both at the cellular and ultrastructural level. During starvation rapid and important changes were noted, particularly in the transverse dimension of cells and organelles. The most striking change, however, was the immediate dilatation of the myocyte T-system, reflecting an adaptive interaction between the intra- and extracellular environment. At the same time exocytosis of intracellular components into the extracellular space of the T-system was observed. The ratio of mitochondria to myofibrils decreased progressively during starvation. Such a decrease, in general, may reach a point when cellular energy supply becomes compromised. A comparison between different regions of the heart showed no differences and it can be concluded that the morphological changes during starvation are the same, and equally distributed, in both ventricles. The changes described in the aged rat heart point in the direction of a hypertrophy of the aged myocyte. This leads to a lower ratio between surface and volume which finds its representation at the subcellular level in a more spherical shape of nuclei and mitochondria. Unlike what is seen in malnutrition, the mitochondrial/myofibril ratio is higher in the older rat. From the morphological point of view, the atrophy of malnutrition and the hypertrophy of ageing are opposed, but in both there is a change in the relationship of the myocyte to its environment which directly influences the substrate exchange capacity. This tends to protect the myocyte in starvation but jeopardizes the older cell.

Beneficial effects of diltiazem on the natural history of hypertensive diabetic cardiomyopathy in rats

Hypertensive diabetic rats develop a cardiomyopathy characterized by systolic and diastolic ventricular dysfunction, myocardial hypertrophy and fibrosis, pulmonary congestion and a very high mortality rate. Alterations in contractile proteins and sarcoplasmic reticular calcium (Ca2+) transport in diabetic myocardium and their partial reversal with verapamil suggest that calcium channel blockade may prevent death from congestive heart failure in hypertensive diabetic rats. A large group of rats with renovascular hypertension and streptozotocin diabetes were divided into four groups: untreated animals (Group 1) and animals treated with 100 (Group 2), 300 (Group 3) or 600 (Group 4) mg/kg per day of sustained release diltiazem mixed in their food. Treatment was begun shortly after the onset of hypertension and diabetes. Mortality rates after 4 months were 59% (19 of 32), 53% (17 of 32), 27% (7 of 26) and 35% (12 of 34) in Groups 1, 2, 3 and 4, respectively; the mortality rate in age-matched control rats was 5% (1 of 19). The reductions in mortality rates in Groups 3 and 4 were statistically significant. Diltiazem did not change systolic blood pressure, serum glucose concentration, heart rate or left ventricular mass. There was a trend to decreased left ventricular interstitial fibrosis and perivascular fibrosis in diltiazem-treated animals. Ventricular collagen concentration was similar in untreated hypertensive diabetic and control rats; levels were higher in hypertensive diabetic rats that died than in those that survived. There was a trend to decreased collagen concentration as diltiazem dose increased. Myosin isoenzyme distribution was not changed in Groups 3 and 4 (in comparison with Group 1). In all hypertensive diabetic groups, rats that died had a higher blood pressure, heart rate, relative left ventricular mass, lung weight and lung water than did survivors. The mortality rate was two to three times higher among rats with an initial blood pressure greater than or equal to 180 mm Hg. The beneficial effects of diltiazem on survival were most significant among rats with severe hypertension.

Capillary neoformation in the rat heart--stereological studies on papillary muscles in hypertrophy and physiologic growth

Stereological investigations on myocardial capillaries provided evidence that the common estimator of capillarity, the capillary density (i.e., number of capillary profiles per unit transverse sectional area), underestimates the true capillary supply since the capillary axes are not oriented perfectly in parallel to the myofiber axes. Recently, we studied the "true" capillarity, i.e., the length density of capillaries (LV = capillary length per capillary volume), in some experimental models of cardiac hypertrophy which have been published elsewhere. It has been shown that LV decreases in renovascular hypertension, but is maintained in physical exercise and after chronic thyroxin application. However, the growth pattern of capillaries in hypertrophic hearts has not yet been analyzed. In the present paper it is demonstrated that important information on the capillary network can be derived from the two-dimensional capillary-to-fiber ratios (2D CFR: capillary profiles per myofiber profiles in transverse sections) and from the three-dimensional capillary-to-fiber ratios (3D CFR: capillary length per unit myofiber length). Increase in both suggests neoformation of additional capillary branches in parallel connection. Retrospective analysis of the quantitative data indicates that in hypertrophy induced by physical exercise or by chronic thyroxin application capillary neoformation in parallel connection counterbalances increase of oxygen diffusion distance due to myofiber enlargement. In renovascular hypertension, capillary neoformation in parallel connection does not occur. Studies on normal growth indicated both a slight decrease of LV of capillaries, as well as a continuous neoformation of additional capillary branches.

A comparison of the pathological spectrum of hypertensive, diabetic, and hypertensive-diabetic heart disease

The hearts obtained at autopsy of 67 patients with hypertension, diabetes mellitus, or both were examined microscopically and histochemically, and the amount of fibrosis was determined. Significant differences in heart weight, interstitial fibrosis, replacement fibrosis, and perivascular fibrosis were found among the groups. The mean heart weight of the hypertensive-diabetic patients was significantly greater than that of the hypertensive patients and the diabetic patients. The amount of microscopic fibrosis increased between the groups, the lowest in hypertensive hearts, midrange in diabetic hearts, and highest in hypertensive-diabetic hearts. Total fibrosis correlated with heart weight among diabetic and hypertensive-diabetic patients and was significantly greater among patients with congestive heart failure, most of whom had histories of both hypertension and diabetes. The microscopic grade of fibrosis correlated significantly (p less than 0.01) with a quantitative, histochemical determination of the amount of collagen per milligram of total noncollagenous protein in the heart tissue. Myocardial fibrosis may contribute to the diastolic dysfunction typical of hypertensive-diabetic cardiomyopathy, in which congestive heart failure is a common sequela. The importance of hypertension in the pathogenesis of severe diabetic heart disease is discussed.

Diabetic heart disease--Part II: The clinical and pathological spectrum

Diabetes mellitus is a significant condition, affecting major segments of all population groups studied. With the introduction of insulin and oral hypoglycemic therapy, together with better understanding of diet and weight control gained over the past half century, the primary causes of diabetic morbidity and mortality have shifted in varying proportions from metabolic derangements, infection, and renal insufficiency to different types of cardiovascular disease. Despite extensive clinical and laboratory research on the etiology, pathogenesis, and even the existence of cardiovascular disease associated with diabetes mellitus, however, considerable debate is still apparent in this field. Our purpose is to present an overview of the subject of diabetic heart disease, with a critical analysis of epidemiologic, clinical, and pathological data. Some of this material will be addressed from the perspective of research in this area over the past decade by one of us (SMF), particularly in experimental hypertensive and diabetic cardiomyopathy. However, overall, an attempt will be made to provide an objective and balanced analysis in order to answer the question: does diabetic heart disease exist?