Effects of hyperkalemia on neonatal endothelium and smooth muscle

Contradictory results have been reported regarding the effect of hyperkalemic cardioplegic or organ preservation solutions on endothelial and smooth muscle cells. The present study was designed to determine the effects of potassium concentrations and exposure times to hyperkalemia on endothelium-derived relaxing factor (nitric oxide) biosynthesis and release, and smooth muscle function in neonatal vessels.

Aortic rings taken from neonatal rabbits were studied in organ baths at physiologic pressure. The effect of Krebs' solution containing 5, 25, 50, or 100 mmol/L potassium incubated for 45 minutes (group 1), St. Thomas' Hospital cardioplegic solution containing 16, 25, 50, or 100 mmol/L potassium for 45 minutes (group 2), and Krebs' solution containing 5 and 50 mmol/L potassium or St. Thomas' Hospital cardioplegic solution containing 16 and 50 mmol/L potassium for 135 minutes (group 3) or 270 minutes (groups 4 and 5) was examined. The rings were then washed and contracted with U46619 (30 nmol/L). The ability to release endothelium-derived relaxing factor (nitric oxide) in response to acetylcholine was tested.

The maximal relaxation induced by acetylcholine did not decrease in any group. Evidence of slight alteration of smooth muscle contraction was seen only in the rings incubated in Krebs' solution with 50 mmol/L potassium for 270 minutes (group 4) with unchanged maximal contraction and sensitivity to potassium (group 5).

We conclude that after exposure for a limited time (4 1/2 hours), hyperkalemia per se does not significantly alter the function of endothelium to release endothelium-derived relaxing factor (nitric oxide) in response to acetylcholine and only slightly alters the contraction speed of smooth muscle in the neonatal rabbit aorta.