NO-cGMP-mediated relaxation is impaired in mesenteric arteries from rats with periodontitis

F. Neto de Jesus, S. A. Teixeira, M. Napolitano, S. K. Costa, M. N. Muscara. Pharmacology, University of Sao Paulo, Sao Paulo, BRAZIL.

Introduction: Periodontal disease has systemic consequences in both humans and rodents, and we have previously described that NO is a key regulator of some these effects on remote organs, such as rat heart, kidney and aorta. In this study, we show the influence of periodontitis on rat mesenteric artery vasomotricity in vitro.

Method: Adult male Wistar rats were anesthetized with ketamine (80 mg/kg, i.p.) plus xylazine (16 mg/kg, i.p.) and periodontitis was induced by the subgingival placement of a cotton ligature around both the left and right lower first molars (group P); sham rats (S) had the ligatures immediately removed. Seven days later, the mesenteric bed was dissected for isolation of the third-branch artery. The vessels were mounted on a wire myograph in order to evaluate the in vitro responses to acetylcholine (ACh), sodium nitroprusside (SNP) and sildenafil (Sil), as well as in the presence of the KATP channel blocker glibenclamide (Gli) or the non selective K+ channel blocker tetraethylammonium (TEA). From the concentration-response curves, potency (pD2) and maximal response (Emax) values were calculated. The vessels were also analysed for COX and NOS isoenzymes mRNA, Western blotting for sGC, catalase (CAT), superoxide dismutase (SOD) and nitrotyrosine-containing proteins (NT), and SOD and CAT enzyme activities. Gingiva samples and ligatures were analysed for the presence of bacterial DNA by PCR. Differences between the groups were analysed by unpaired Student t-test.

Results: ACh, SNP and Sil showed significantly lower relaxant potencies in arteries from group P than S; the respective pD2 values were 7.9±0.2 (n=5) vs. 7.3±0.1 (n=5; P<0.05), 7.1±0.1 (n=6) vs. 6.4±0.2 (n=7; P<0.01) and 10.3±0.2 (n=9) vs. 8.6±0.2 (n=7; P<0.001); Emax values remained unaltered. In the presence of TEA or Gli, the differential responses to ACh and SNP were abolished. Arteries from group P showed significantly increased iNOS mRNA [1.0±0.1 (n=9) vs. 20.9±5.9 (n=5; P<0.01)], NT [77.5±11.8 (n=10) vs. 122.6±15.1 (n=7; P<0.05)] and CAT activity [2.3±0.2 (n=5) vs. 3.2±0.3 (n=5; P<0.05)] parallel to lower SOD activity [0.7±0.1 (n=5) vs. 0.4±0.1 (n=5; P<0.01)] in comparison with group S. Significantly increased bacterial DNA was found in gingiva and ligatures collected from group P in comparison with group S [24.0±4.4 (n=5) vs. 47.4±8.2 (n=5; P<0.05)].

Conclusions: During the early phase of ligature-induced periodontitis in rats, functional changes related to the NO-sGC-cGMP pathway occur in the mesenteric artery, which may be secondary to impaired hyperpolarization and/or nitration of tyrosine residues of selected proteins.