H2 RECEPTOR-MEDIATED RESPONSES OF AORTIC ENDOTHELIAL-CELLS TO HISTAMINE

It is well known that umbilical vein endothelial cells express H-1 receptors that mediate the various responses of these cells to histamine, including accumulation of inositol phosphates, rise of cytosolic Ca2+, increased permeability to macromolecules, and release of prostacyclin. In bovine aortic endothelial cells, histamine did not increase the level of inositol phosphates nor the release of prostacyclin. In contrast, it increased the adenosine 3',5'-cyclic monophosphate (cAMP) content of these cells. That response was obtained in the 1 to 100-mu-M range of concentrations and reached a maximum within 2 min of histamine addition. It was mimicked by the H-2-specific agonist dimaprit, inhibited by the H-2 antagonist ranitidine, and insensitive to the H-1 antagonist mepyramine. Histamine reduced the permeability to albumin of bovine aortic endothelial cell monolayers; this paradoxical effect is likely to be mediated by the rise in cAMP, which is known to enhance the barrier property of the endothelium. In conclusion, bovine aortic endothelial cells are responsive to histamine, and this response is mediated by H-2 and not H-1 receptors.