Aerobic exercise increases tear secretion in type 2 diabetic mice

Purpose. To investigate the effects of exercise on tear secretion in type 2 diabetic mice, and to investigate the effect of the adenosine monophosphate-activated protein kinase (AMPK) activator 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR). Methods. Heterozygous controls (db/m; m Lepr^db) and type 2 diabetic mice (db/db; Lepr^db) either underwent forced treadmill exercise training 5 days a week or remained sedentary for 8 weeks. Tear secretion volume was measured by cotton threads for 30 seconds pre- and post intervention. The levels of oxidative stress markers (8-hydroxy-20-deoxyguanosine [8-OHdG], propanoyl lysine [PRL], and hexanoyl lysine [HEL]) in tears were measured in the postintervention period. Furthermore, C57BL/6JJc1 mice, db/db mice, and db/m mice received a single intraperitoneal injection of AICAR or PBS each day for 5 days, and tear secretion volume was measured. Results. Exercise training for 8 weeks increased tear secretion volume in db/m and db/db mice. The levels of oxidative stress markers in tears were less in the exercise group than in the control group. In C57BL/6JJc1 mice, the tear secretion volumes in both the AICAR 125 mg/kg and AICAR 250 mg/kg groups were significantly larger than in the PBS group (P < 0.01 and P < 0.01, respectively). Additionally, in db/db mice, tear secretion volume in the AICAR 125 mg/kg group was also significantly larger than in the PBS group (P < 0.05). Conclusions. Exercise training for 8 weeks and a daily injection of AICAR for 5 days increased tear secretion in mice. The results suggest that exercise may be a potential therapy to modulate tear secretion.