Zero-stress states of the main pulmonary arteries and aorta and small systemic arteries were determined in 22 nondiabetic and 29 streptozocin (STZ)-induced diabetic rats. The zero-stress state of each vessel was obtained by cutting the vessel transversely into a series of short rings, then cutting each ring radially, which caused the ring to spring open into a sector. Each sector can be characterized by its opening angle. The opening angle has strong regional dependence. In some regions of rat arteries, the opening angle can be >360°. Rats were studied 5, 10, 20, 30, and 40 days after an injection of 75 mg/kg body wt i.v. STZ. During diabetes development, the opening angles in general increased and reached a plateau in ∼30 days. The maximum change of opening angle over normal lies in the range of 18–105°, depending on location. The pulmonary arteries were affected by diabetes as much as the systemic arteries. The course of change of the opening angle during diabetogenesis was different from those of the serum glucose level and blood pressure. Blood pressure in carotid, external iliac, and pulmonary arteries did not change significantly in diabetogenesis. To clarify the physiological meaning of the opening angle, we measured the circumferential strain in the blood vessel wall in homeostatic condition and the residual strain at the no-load state, with both strains referred to the zero-stress state. We calculated the corresponding stresses in the vessel wall. The circumferential stress in the vessel wall was greatly increased by diabetes; great errors will result if the opening angle is ignored.

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