Effect of experimentaly induced diabetes on the rat's heart: influence of tocopherol as antioxidant [a morphological and a morphometric study]

ABSTRACT

The present work aimed to study the effect of vitamin E supplementation on diabetic cardiomyopathy. This was achieved by comparing the normal control group [group I], alloxan induced diabetic group [group II] versus vitamin E-treated diabetic group III. This was clarified by studying these groups as regards cardiomyocytes, connective tissue matrix and blood vessels [coronary arteries and capillaries] in an attempt to find out if this vitamin could protect against diabetic cardiomyopathy. The following parameters were measured for all groups non fasting blood glucose levels; plasma tocopherol concentrations, body and heart weight. For histological study of the myocardium, all animals were subjected to the following techniques morphometric study for the myofiber diameters and the numerical densities of blood capillaries/ mm[2] of the examined tissues, paraffin sections stained with HX and E, Masson's trichrome and PAS, cryostate sections stained with succinic dehydrogenase, and alkaline phosphatase, and ultrastructural study. There was a significant increase in non fasting blood glucose levels [370 +/- 55mg/dL] in group II animals if compared with that [100 +/- 20 mg/dL] of group 1 healthy animals. While in alloxan diabetic /vitamin E treated group III the non fasting blood glucose levels were [180 +/- 30 mg/dl] not too higher than that in group I. Plasma tocopherol concentrations for group III animals [12.7 +/- 0.5 mg/dl] were significantly increased of about 66 +/- 0.14 percent more than that [8.4 +/- 0.4 mg/dl] in the control group I. This means that the concentration of Eocopherol in the plasma was significantly influenced by feeding the animals a vitamin E-enriched diet for 16 weeks starting soon after inducing diabetes. This vitamin E- enriched diet used for group III animals nearly preserved both body and heart weights, which were significantly reduced in diabetic animals fed on the standard diet. Morphometric study showed a significant decrease in myofiber diameter observed in focal areas of the myocardium of alloxan diabetic rats. The cause of this result could be attributed to focal structural alterations affecting the cardiomyocytes. These structural changes included disorganization of the myofibrils at the Z lines, transverse tearing and distortion of intercalated discs and presence of contraction bands. There were also deterioration and fragmentation of myofilaments leading to loss of cross and longitudinal striations, crestolysis of mitochondria and cytoplasmic vacuolation. The intramural coronary arteries had thickened basement membranes and thickened walls due to deposition of more collagen fibers in their adventitia, and these changes might impair their elasticity and elastic recoil. These stressed blood vessels often lead to myocardial ischemia due to impairment of blood flow. The interstitial blood capillaries in the myocardium of diabetic group II showed an increase in their numerical densities /mm[2][CD[s]]. This increase was about 5 +/- 0.06 percent more than that in the control group I. This increase in CDs could be owed to the need to maintain good microvascularity, even in diabetic state, to protect the myocardium from ischemic damage. Many, not all of these capillaries appeared partially collapsed with thickened basement membranes. This was due to increase in the amount of connective tissue fibers especially collagen in the precapillary locations. These collapsed capillaries were observed to retain blood in their lumena, and this indicated that these capillaries impeded the influx of blood. The endothelial cells lining these capillaries appeared swollen and rich in biosynthetic organelles e.g. rER, ribosomes, mitochondria and Golgi bodies with the associated vesicles. This explains the effort exerted by these cells to synthesize new fibers added to their basement membranes in an attempt to compensate the degenerative changes associated with diabetes. Tocopherol acetate-enriched diet used instead of the standard diet to feed diabetic animals of group III was cardio protective and largely prevented severe alterations of myocardial structure typically observed after an alloxan diabetes duration of 16 weeks [group II]. Deterioration and fragmentation of myofilaments were seen less, the areas of degeneration and of contraction bands were clearly reduced, the abundant collagen fiber deposits especially at precapillary locations and in the wall of coronaries were significantly reduced. It could be concluded that the oxidative stress plays a significant role in the disturbances of cardiac structure in diabetes. Antioxidants such as alpha tocopherol are able to prevent these adverse effects despite the elevated blood glucose levels. It seems likely that adjuvant treatment with antioxidants is needed to maintain a healthy balance in diabetic patients with multiple complications. Therefore it would seem wise to supplement all diabetics with vitamin E either from natural or medicinal sources to retard or even prevent the occurrence of complications especially cardiomyopathy