高脂肪食による肥満後に通常の食事を再開すると、Wistar系ラットの唾液組成の変化が回復する

Re-establishing normal diet following high fat-diet-induced obesity reverses the altered salivary composition in Wistar rats.

抄録

背景 肥満は唾液の分泌障害に関与していると言われている。本研究では、食事誘発性肥満が唾液分泌に及ぼす影響を評価し、通常の食事を再び与えることが食事誘発性肥満に伴う唾液分泌の変化にどのように影響するかを検討することを目的とした。方法 体重55～65gの離乳期ラットを無作為に7匹ずつ3群（対照群、食事誘発性肥満群、再給餌肥満群）に分けた。食事誘発性肥満群には高脂肪食を15週間与え、再摂食肥満群には高脂肪食を15週間与えた後、さらに15週間通常食を与えた。投与後、血液と刺激唾液を採取し、総タンパク質、電解質、アミラーゼ、Immunoglobulin A（IgA）、レプチン、グレリンを分析した。また，顎下腺の組織総蛋白質，一酸化窒素濃度，Na+/K+-ATPase，muscarinic(M3)受容体，アクアポリン5の発現量を測定した。データは平均±SEMで表示し、独立した学生t-testおよびANOVA（Tukey's post-hoc test付）を用いて比較した。結果 唾液中のカルシウム，リン酸，重炭酸，レプチンが増加し，唾液中のアミラーゼ，グレリンは対照群に比べて減少した。これらの変化のほとんどは、再給餌された肥満群で逆転した。肥満群と対照群との間では，顎下腺における唾液ラグタイム，流量，組織総蛋白質，一酸化窒素，M3受容体，Na++/K+-ATPase，アクアポリン5の相対的発現量に有意な差は認められなかった。結論 食事誘発性肥満は唾液因子の変化をもたらすが，それは通常の食事に戻すことで回復することがわかった。

Background Obesity has been implicated in impaired salivary secretion. This study aimed at evaluating the influence of diet-induced obesity on salivary secretion and how re-feeding with normal diet would affect changes in salivary secretion associated with diet-induced obesity. Methods Weaning rats weighing 55-65 g were randomly divided into three groups (control, diet-induced obese, re-fed obese) of seven rats each. The diet-induced obese group was fed a high-fat diet for 15 weeks, whereas the re-fed obese group received normal diet for another 15 weeks following the 15 weeks of high-fat diet. After treatment, blood and stimulated saliva samples were collected for the analyses of total protein, electrolytes, amylase, Immunoglobulin A (IgA), leptin and ghrelin. Tissue total protein, nitric oxide level, expressions of Na+/K+-ATPase, muscarinic (M3) receptor and aquaporin 5 in the submandibular glands were determined. Data were presented as mean±SEM and compared using independent student t-test and ANOVA with Tukey's post-hoc test. Results Results indicated increases in the levels of salivary calcium, phosphate, bicarbonate and leptin, whereas the levels of salivary amylase and ghrelin showed reduction in the obese group compared with the control. Most of these changes were reversed in the re-fed obese group. There were no significant differences in salivary lag time, flow rate, levels of tissue total protein, nitric oxide and the relative expressions of M3 receptor, Na++/K+-ATPase and aquaporin 5 in the submandibular glands between the obese and control groups. Conclusions Diet-induced obesity lead to some changes in salivary factors which were reversed by returning to normal diet.