ENDOTHELIAL NITRIC-OXIDE SYNTHASE IS DOWN-REGULATED DURING HYPERDYNAMIC SEPSIS

Although studies have shown that endothelium-derived nitric oxide (NO) release is depressed during endotoxic shock or polymicrobial sepsis, it remains unknown whether the decreased release of endothelium-derive d NO during the hyperdynamic stage of sepsis is due to downregulation of endothelial NO synthase. To study this, adult rats were subjected t o sepsis by cecal ligation and puncture (CLP). At 10 h after CLP (i.e. , hyperdynamic sepsis) or sham operation, the aorta was removed and a monoclonal antibody against endothelial (constitutive) NO synthase (E- NOS) was used to determine the immunohistochemical presence and electr on microscopic localization of E-NOS in rat aortic endothelial cells. Image analysis was used to quantify aortic E-NOS. In additional groups of animals, the aorta was isolated at 10 h after CLP and the vascular responses to an endothelium-dependent vasodilator, acetylcholine, and an endothelium-independent vasodilator, nitroglycerine, were determin ed. The results indicate that the number of E-NOS negative endothelial cells increased from 7% in shams to 22% in septic animals. E-NOS dens ely labeled endothelial cells were significantly reduced from 20% to 8 % at 10 h after CLP. The E-NOS positive area in aortic endothelial cel ls was reduced from 26.1 +/- 1.0 mu m(2)/standard frame in sham to 22. 3 +/- 0.9 mu m(2)/standard frame in septic animals. Moreover, acetylch oline-induced but not nitroglycerine-induced vascular relaxation was s ignificantly depressed at 10 h after the onset of sepsis. These result s, taken together, indicate that the decreased E-NOS in the vascular e ndothelial cell is at least in part responsible for endothelial cell d ysfunction (i.e., the reduced endothelium-derived NO release) observed during the early, hyperdynamic stage of polymicrobial sepsis.