MYOGENIC ACTIVATION OF CANINE SMALL RENAL-ARTERIES AFTER NONCHEMICAL REMOVAL OF THE ENDOTHELIUM

Myogenic activation of isolated small arteries (200-500 mu m) of the dog kidney was evaluated by measuring vessel diameters during stepwise elevations of transmural pressure before and after removal of the endothelium by mechanical rubbing or air perfusion. Myogenic activation was unaffected by mechanical rubbing, but air perfusion caused the arteries to constrict and attenuated the myogenic response; i.e., vessel diameters increased as transmural pressure was elevated. However, air-perfused arteries still constricted in response to norepinephrine and dilated during superfusion with Ca2+-free solution, demonstrating that loss of the myogenic response did not result from an inability of the vessel to contract. Intact arteries contracted with 1 mu M norepinephrine exhibited normal myogenic responses, demonstrating that loss of myogenic activation in the air-perfused vessels was not a nonspecific effect secondary to constriction of the artery. These results suggest that myogenic activation of small renal arteries is independent of the endothelium and that the method of endothelial removal may affect conclusions regarding the role of the endothelium in mediating the myogenic response.