Effects of mitiglinide on glucose-induced insulin release into the portal vein and fat-induced triglyceride elevation in prediabetic and diabetic OLETF rats

Objective: The effect of single-dose mitiglinide on glucose and lipid metabolism was examined in OLETF rats with spontaneous type 2 diabetes in which the early insulin response following glucose challenge is known to diminish over time and become lost with aging. Methods: (1) With catheters inserted into the portal veins, 12-wk-old prediabetic OLETF rats were given an OGTT of 1g/kg after 17 h of fasting. Eight rats each were orally given mitiglinide 1 mg/kg, nateglinide 50 mg/kg, or glibenclamide 1 mg/kg, vs 0.5% carboxy-methylcellulose (CMC) as control, and were given an OGTT immediately afterward. Following oral administration of mitiglinide, nateglinide, glibenclamide, or 0.5% CMC, the 24-wk-old overt-diabetic OLETF rats were immediately given an, OGTT of 1g/kg. (2) After 17 h of fasting, 24-wk-old OLETF rats were subjected to a fat-loading test. Eight rats each were given mitiglinide 3 mg/kg, glibenclamide 1 mg/kg, or glimepiride 1 mg/kg, vs 0.5% CMC, and were given soy oil 2 g/kg immediately afterward. They were also given mitiglinide orally and examined for LPL mRNA expression in their adipose tissue. Results: (1) After OGTT, mitiglinide produced a significant increase in portal insulin levels 15 min after its administration, as well as a significant decrease in peripheral glucose levels 15–120 min after its administration in the OLETF rats. Like-wise, nateglinide produced an increase in portal insulin levels and a decrease in peripheral glucose levels shortly after its administration in these rats. Glibenclamide increased portal insulin levels for an extended time after its administration, and significantly decreased peripheral glucose levels in the rats 120–300 min after its administration in the rats. In contrast, as in the 12-wk-old rats, a precipitous rise in insulin secretion was seen in the portal vein of 24-wk-old rats given mitiglinide, which peaked 15 min after mitiglinide administration, but the insulin levels continued to increase for 120 min or longer in the 24-wk-old rats given glibenclamide. In addition, as in the 12-wk-old rats, a significant decrease in glucose levels in peripheral blood was noted 30 and 60 min after mitiglinide administration and 300 min after glibenclamide administration in the 24-wk-old rats. (2) Mitiglinide increased LPL mRNA expression 120 min after its administration, and significantly decreased peripheral TG and chylomicron-TG levels after fat challenge in the 24-wk-old OLETF rats. Conclusion: Mitiglinide exhibited fast-onset and short-acting insulin-secretagogic effects, inhibiting post-glucose challenge increases in glucose levels and post-fat challenge increases in TG levels.