To clarify the relationship between
diabetes mellitus and
carbohydrate digestion, the activities of
sucrase and
isomaltase, which form a complex
enzyme (SI complex) on the brush border membranes, were compared in the progression of
diabetes mellitus in Otsuka Long-Evans Tokushima fatty (OLETF) rats, a model of human
non-insulin-dependent diabetes mellitus with
insulin resistance, and Long-Evans Tokushima Otsuka (LETO) rats as non-diabetic controls. Until 40 weeks of age, OLETF rats were obese and had a high plasma
glucose level, compared to age-matched LETO rats, but the
sucrase and
isomaltase activities showed no significant differences between the two strains. Oral
glucose tolerance test revealed that during 40-48 weeks of age,
NIDDM became very severe with advancing
insulin resistance in OLETF rats. In OLETF rats, in contrast to LETO rats, at 48 weeks of age, abnormal increases in the
sucrase and
isomaltase activities occurred, along with a remarkable decrease in
body weight and a further great increase in the plasma
glucose level in the non-fasting state.
Hyperinsulinemia occurred in 20-week-old OLETF rats; however, at 40 and 48 weeks of age, the plasma
insulin level in the non-fasting state in OLETF rats was not significantly different from that in LETO rats. The level of
mRNA encoding the SI complex increased abnormally in 48-week-old OLETF rats. These results suggest that the advance of
insulin resistance leads to an increase in the expression of the SI complex on the transcriptional level.