Endothelium-dependent relaxation to acetylcholine in the aorta of streptozotocin induced diabetic-rat and the BB-diabetic rat.

Experiments were designed to investigate the phenomenon of endothelium-dependent relaxation (EDR) to acetylcholine in two animal models of insulin dependent diabetes mellitus. Thoracic aortas obtained from streptozotocin diabetic rats and genetically diabetic biobreeding rats (BB rats) were used in this study. Concentration-effect curves to acetylcholine were carried out on aortic rings under isometric tension. Following the induction of diabetes with streptozotocin, half of the animals were treated with daily intermediate acting insulin and the other half maintained without insulin for a period of 12 weeks before the experiment. The diabetic BB rats were also maintained on insulin. The EDR to acetylcholine was not impaired in the aortas of streptozotocin diabetic rats (insulin treated as well as untreated) compared to nondiabetic controls. The scanning electron microscopic (SEM) appearances of the aortic endothelium did not differ among the three groups of animals. However, the EDR to acetylcholine was found to be impaired in the aortas of diabetic BB rats. (Maximum relaxation: 25.3 +/- 5.0% of the contraction to norepinephrine compared to 52.2 +/- 5.3% in controls.) The SEM appearances of the aortic endothelium in the diabetic BB rats were found to be abnormal with edema and loss of definition of cell margins compared to nondiabetic controls. The differences in EDR to acetylcholine seen between the two animal models of diabetes may be related to the different aetiologies of diabetes in the animals.