Ameliorated effect of L-arginine supplementation on gingival morphology incyclosporin-treated rats

Background: The role of nitric oxide (NO) in the pathogenesis of cyclospori n (CsA)-induced gingival overgrowth is unknown. The purpose of the present study was to evaluate the effect of NO substrate (L-arginine) and blockade (N-nitro-L-argjnine methylester-hydrochloride, L-NAME) on the gingival morp hology in CsA-fed rats. Methods: Sixty CsA-fed (10mg/kg/day) male Sprague-Dawley rats were assigned to 3 groups. Animals in 2 experimental groups received L-arginine (1% weig ht/weight) in rat chowder or L-NAME (50 mg/l) in drinking water, respective ly, for 4 weeks. Rats in the control group were fed a normal diet and water . At week 0, 2, and 4, dental stone models were made from the mandibular an terior region and the gingival dimensions (width, depth, and height) were m easured. The tail cuff blood pressure and the plasma nitrate level were als o measured at week 4 to monitor the effects of L-arginine and L-NAME treatm ent. Results: No significant difference in the gingival dimensions was noticed a t week 0; however, significant differences were observed at weeks 2 and 4, except the buccolingual depth at week 2. While the magnitude of gingival di mensions was large, moderate, and small in control, L-NAME, and L-arginine groups, respectively, we found significantly reduced gingival dimensions in both L-arginine supplement and L-NAME groups. Nevertheless, the reduced gi ngival overgrowth in the L-NAME treatment group was far less than that in t he exogenous NO treatment group. Plasma NO2-/ NO3- concentrations were also significantly different; i.e., from the highest to the lowest levels were the L-arginine, CsA control, and L-NAME group, respectively. A significantl y increased mean and diastolic blood pressure was found in the L-NAME group compared to the L-arginine group. Conclusions: Gingival morphology in CsA-fed rats was evaluated after NO sub strate (L-arginine) and blockade (L-NAME) treatment for 4 weeks. Significan tly decreased dimensions were noted in the L-arginine group compared to the CsA group at weeks 2 and 4. Although an inhibitory effect on the gingival morphology was also observed in the L-NAME group, another unknown mechanism might be involved. Within the limitations of the study, we suggest that NO may have an important role in the mechanism of CsA-induced gingival overgr owth.