Effect of insulin on naturally occurring gingivitis rats with diabetes.

It is well known that diabetes mellitus aggravates both the severity and progression of periodontal disease. We sought to further explore biologic mechanisms of this relationship using naturally occurring gingivitis rats (ODUS/Odu) rendered diabetic by 65 mg/kg intravenous injection of streptozotocin (STZ). Insulin was administered daily to one group of the rats beginning 4 weeks after STZ injection (STZ-insulin group). Others received no insulin (STZ group). A third group that received no STZ was kept as controls. Eight weeks after STZ injection, sterilized liquid paraffin was injected peritoneally into all three groups, and peritoneal macrophages were collected 4 days later. Macrophage chemotaxis was measured by the membrane filter method using a 48-well microchemotaxis chamber with zymosan activated serum used as a chemotactic stimulant. Blood glucose levels, body weight, plaque indices, pocket depths, serum triglyceride and hemoglobin A1C levels were also determined. We found that blood glucose levels, body weight and triglycerides recovered to normal values in the STZ-insulin group. Further, control of blood glucose resulted in diminished plaque indices, and pocket depths returned to values seen in the controls. Chemotaxis and phagocytosis of peritoneal macrophages improved slightly in the STZ-insulin group, but did not return to levels seen in the pretreatment state. Although insulin resulted in some improvement in leukocyte function damaged by induced diabetes mellitus, recovery was incomplete.