Endothelial cell loss enhances the pressor response in resistance vessels

The role of the endothelium in pressor and relaxation responses was studied using the isolated, perfused mesenteric arterial bed of the rat. Perfusion of mesenteric beds with distilled water for 10 min resulted in endothelial cell loss. This procedure produced no morphological injury to the medial smooth muscle cells as seen by transmission electron microscopy. Such endothelial cell removal resulted in an increase in pressor responses to angiotensin II, epinephrine, norepinephrine and serotonin. Removal of the endothelium either markedly reduced or eliminated the vasodilation response to acetylcholine, whereas it did not alter the vasodilation response to diazoxide. These results show that loss of endothelial cells in resistance vessels results in a marked enhancement of the pressor response to several endogenous vasoconstrictor agents. Thus endothelial cell products may be important in the regulation of local blood flow and resistance. These results could have important implications in disease states in which there might be endothelial cell dysfunction.