Effects of Vasoconstrictors on Isolated Rabbit Coronary Arteries Exposed to Isotonic Iohexol: Potassium Chloride-, Histamine-, Endothelin-, and Prostaglandin-F2??-Induced Contractions on Arteries Exposed to Iohexol without and with Osmotic Additions (Sodium Chloride or Glucose)

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Abstract
A major effect of contrast media (CM) on coronary vessels is vasodilatation, but occasionally, both ionic and nonionic media may cause coronary artery spasm. The influence of CM on the actions of vasoactive substances is not well known. To investigate the effects on rabbit coronary arteries of an iso-osmolar nonionic CM, iohexol (140 mg I/mL) the vasoconstrictors potassium chloride (KCl), histamine, endothelin, and prostaglandin-F2 alpha (PGF2 alpha) were used. The effects of iohexol with 30 to 150 mM sodium chloride (NaCl) or with 25-50 g/L glucose also were investigated. Coronary artery segments were mounted between two L-shaped prongs in tissue baths with buffer solution. Before each investigation, buffer was exchanged with iohexol solution. Increasing concentrations of a vasoconstrictor were added, and the constriction of the vessels was recorded. Iohexol caused a comparatively small inhibition of the contractile effects of histamine and endothelin. This meant little reduction in maximal contraction (Emax), and the concentration of constrictory substance resulting in half maximal contraction (EC50) compared with buffer solution. Iohexol also caused a small reduction in Emax of KCl, but EC50 was significantly lower. Adding NaCl or glucose to iohexol decreased Emax and increased EC50. Iohexol inhibited most of the contractile effect of PGF2 alpha, but adding NaCl increased Emax slightly. The effects caused by a nonionic CM on coronary arteries cannot be attributed to osmolality alone. The CM influenced the effects of vasoconstrictors to differing degrees, but the inhibition of the CM per se was usually small.

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