MEASUREMENT OF NITRIC-OXIDE SYNTHASE ACTIVITY IN SECTIONS OF RAT-LIVER

In the previous communication we described a histochemical method for measuring soluble guanylate cyclase (sGC) activity in sections of rat liver. In theory, this method could be used to assess nitric oxide syn thase (NOS) activity by the increased sGC activity induced by the addi tional presence of the substrates for NOS activity, We found that this was correct provided that the concentration of the colloid stabilizer in the reaction medium was decreased to just below the concentration required to fully stabilize the guanylate cyclase activity in the sect ions. This was related to the fact that the site of NOS activity was d ifferent from that of the sGC activity in the hepatocytes, so that the NO generated had to diffuse from the Kupffer cells to the hepatocytes as could occur only in partially unstabilized sections. Optimal conce ntrations of arginine and of NADPH have been determined for demonstrat ing NOS activity; the increased reaction was shown to be largely inhib ited by methyl-arginine.