Structural Changes in the Cardiac Microvasculature of the Rat in Response to Acute High Glucose Levels: A Comparison With Diabetes

Objective : Isolated rat hearts were used to determine whether structural changes in the coronary microcirculation caused by diabetes mellitus occur soon after the onset of hyperglycemia and whether early changes might be reversed by return to normoglycemic conditions. Methods : Three experimental groups of hearts were used. The perfusate was Krebs‐Henseleit medium with the addition of (a) 25 mmol/L glucose for 60 minutes, (b) as (a) followed by 5 mmol/L glucose for 30 minutes, and (c) hearts from diabetic rats perfused for 15 minutes. All the hearts were fixed and processed for electron microscopy. Measurements were made of various capillary dimensions and basal lamina thickness. Results : The high glucose concentration caused an overall reduction in capillary dimensions which was partly reversed by reperfusion with 5 mmol/L glucose. Diabetic hearts showed enlarged whole capillary and luminal area and thinning of the endothelial cells without any change in cross‐sectional area. Endothelial gaps, consistent with increased permeability, were observed in the high glucose group but not in diabetic hearts. The basal lamina was thickened in all three experimental groups compared with controls. Conclusions : The results show that morphological changes in the microcirculation occur much earlier than was previously thought and, with the possible exception of the basal lamina thickening, may be reversible.