The Effects and Mechanism of Action of Cimetidine on Inducible Nitric Oxide Synthase Using an Equine Soft-Tissue Inflammation Model.
Date of Award
Doctor of Philosophy (PhD)
Veterinary Physiology, Pharmacology, and Toxicology (Veterinary Medical Sciences)
Charles R. Short
Cytochrome P-450 (CYP) and inducible nitric oxide synthase (iNOS) are similar heme containing enzymes. Cimetidine (CIM) is an H2 antagonist, and since CIM inhibits CYP, it may also bind to the heme-iron of NOS and reduce NO generation. Six horses each had three tissue chambers inserted subcutaneously on either side of the neck for Trial 1. Trial 2 also used 6 female Thoroughbred horses implanted with at least two tissue chambers as in Trial 1. Blood and tissue chamber fluid (TCF) were sampled at -24, 0, 4, 8, 12 h and at 1, 2, 3, 5, and 7 days after carrageenan instillation for Trial 1 a similar schedule was used for Trial 2. Tissue chamber fluid (TCF) interleukin (IL)-1 concentrations were increased following NaCl inflamed (NaCl-I), CIM, or aminoguanidine (AG) treatment when compared to non-inflamed chamber TCF. For IL-6, NaCl-I and CIM were significantly increased when compared to NaCl non-inflamed (-N). There was no significant difference between the area under the curve (AUC) of IL-1 or IL-6 in NaCl-I TCF vs. CIM or AG TCF. Cimetidine significantly decreased NO3 - AUCs in plasma. Aminoguanidine and CIM decreased NO3 - AUCs in TCF in Trials 1 and 2. These results indicate that CIM had an effect on some inflammatory indices in this model. Surprising is the inhibition of NO3- formation by CIM. This could be the result of direct inhibition of NOS, direct inhibition of CYP, and/or an interaction at H2 receptors that have a role in the regulation of NOS. For CIM, classical Type II spectra, similar to those previously reported, were obtained at concentrations ≥0.1 mm in both rat and equine hepatic microsome preparations. Both hexobarbital and AG produced a Type I difference spectra in rat and equine hepatic microsome preparations. The interaction of CIM with a leukocyte preparation resulted in atypical spectra, but provided evidence for interaction with a chromophore in TCF. Cimetidine also did not affect the conversion of NO to NO3- catalyzed by hemoglobin. Western blot analysis, however, failed to identify NOS in the leukocyte preparation.
Hunter, Robert Paul, "The Effects and Mechanism of Action of Cimetidine on Inducible Nitric Oxide Synthase Using an Equine Soft-Tissue Inflammation Model." (2000). LSU Historical Dissertations and Theses. 7201.