NOREPINEPHRINE AND ILOPROST IMPROVE BARRIER FUNCTION OF HUMAN ENDOTHELIAL-CELL MONOLAYERS - ROLE OF CAMP

The barrier function of human artery endothelial cells was improved by addition of agents that increase the cellular adenosine 3',5'-cyclic monophosphate (cAMP) concentration. Together with a decrease in the passage rate of peroxidase, an increase in the transendothelial electrical resistance was observed. A direct correlation was found between the relative increases in cellular cAMP concentration and the relative decrease in peroxidase passage after incubation of the cells with forskolin (0.25 and 2.5-mu-M), the beta-adrenergic agonist isoproterenol (10-mu-M), and the stable prostacyclin analogue iloprost (10-mu-M). Norepinephrine (10-mu-M) reduced the peroxidase passage to a much larger extent (40% reduction) than might be expected on the basis of a small increase of cAMP concentration. This small increase in cAMP (44%) was the result of interactions of norepinephrine with beta-adrenergic receptors, which increase cAMP, and alpha-adrenergic receptors, which decrease cAMP. The relatively strong reduction in permeability (also found in the presence of the alpha-adrenergic antagonist phentolamine) suggests that an additional cAMP-independent mechanism underlaid the barrier-improving effect of norepinephrine. A marked elevation of cAMP by forskolin was accompanied by a disappearance of Factin and myosin from stress fibers. They were found diffusely spread over the cell, and F-actin in the cell periphery became prominently visible.