A novel immunohistochemical semiquantitative technique for endothelial constitutive nitric oxide synthase...

It has been difficult to quantify protein production in small pathological specimens by conventional techniques. We describe a new method for semiquantification of immunohistochemical staining, which involves application of the enzyme-labeled avidin (LAB) technique, coupled with an ultra-sensitive and fast chemiluminescent substrate for alkaline phosphatase. The entire procedure can be completed in less than 3 hr. The final step involves X-ray film exposure for 30 min, and the optical density of the subsequent images is examined with a microcomputer imaging device. The optical densities are translated into relative protein concentrations by a reference standard curve, obtained via an immunoblot. To establish a model for semiquantification of endothelial constitutive nitric oxide synthase (eNOS) protein, we compared the coronary arteries of WKY rats fed a normal chow diet to the coronary arteries of WKY rats fed a cholesterol diet. Using this technique, we have found a relative 130-fold decrease in eNOS in the cholesterol-fed group compared to the normal chow-fed group.