Vasomotor changes in isolated coronary arteries from diabetic rats

Contractile responses to prostaglandin F2 alpha, serotonin, noradrenaline, and potassium were examined in isolated intramyocardial arteries of Wistar rats 8 weeks after the induction of diabetes mellitus by administration of streptozotocin (STZ). The concentration-response curves obtained were compared with those noted in vessels both from age- and from weight-matched control rats. Light and electron microscopy did not reveal any major change in coronary artery wall thickness or morphology. There was no difference in the pattern of vasomotor responses between the two control groups. Contractile responses to prostaglandin F2 alpha, and potassium were significantly reduced, while contractile responses to serotonin and noradrenaline were unaltered in coronary arteries from diabetic rats. The vasomotor responses to noradrenaline and potassium showed a biphasic pattern in control vessels, i.e. contraction noted at high agonist concentrations was preceded by slight, but reproducible relaxation at lower concentrations. In diabetic vessels these relaxant responses were absent. The contraction produced by noradrenaline was markedly enhanced by the presence of propranolol in both diabetic and control vessels. Dilator responses to verapamil, diltiazem, nifedipine, papaverine and magnesium were studied in serotonin-precontracted coronary arteries; the concentration-response curves obtained by verapamil and diltiazem were shifted to the right in diabetic vessels. It appears justified to use vessels from age-matched rats as controls when vasomotor reactivity in coronary arteries from STZ-diabetic rats is investigated. The reduction in contractile responses to prostaglandin F2 alpha and potassium, and the reduction or lack of relaxant responses to noradrenaline, potassium, verapamil and diltiazem, in diabetic coronary arteries, indicate a selective modification of the coronary circulation by the diabetic disease.