Insulinotropic response to enterally administered succinic and glutamic acid methyl esters.

Both the monomethyl and dimethyl esters of succinic acid, administered enterally to fasted rats, caused a rapid increase in plasma insulin. Such was not the case, however, after enteral administration of either succinic acid or the dimethyl ester of glutamic acid. The time course for the appearance of radioactive material in plasma was also vastly different after enteral administration of either [1,4-14C]succinic acid or its dimethyl ester. In the latter case, the separation of acidic and nonacidic radioactive metabolites and the measurement of 14C-labelled D-glucose indicated that, after enteral administration of succinic acid dimethyl ester (2 mmol), its initial appearance rate in plasma averaged 45 +/- 9 microM/min resulting, after 120 min, in a plasma concentration of 1.34 +/- 0.14 mM.