INS and diabetes mellitus: Plasma insulin and C-peptide decreased significantly in Group II compared to Group I. We observed no significant differences in serum insulin and C-peptide concentrations between TNTL- (1.26 and 0.63 g/kg) and metformin- (210 mg/kg), gliclazide- (37 mg/kg) treated rats, and untreated STZ-induced DM groups.