In rats with adjuvant arthritis measurements were taken of the urinary excretion of nitrate, reflecting endogenous nitric oxide (NO) formation, and cyclic guanosine monophosphate (cGMP).
Urinary nitrate was determined by gas chromatography, cGMP by radioimmunoassay.
A significant (p < 0.001), more than three fold increase of urinary nitrate excretion was found in rats 20 days after induction of adjuvant arthritis compared with non-arthritic rats. There was no significant difference in urinary cGMP excretion between arthritic rats and control animals.
The data suggest that the dramatic increase of urinary nitrate excretion is due to increase of NO synthesis by the inducible form of NO synthase.