Postprandial insulin secretion is modulated by both neural and humoral gastrointestinal insulinotropic factors in addition to the absorbed nutrient. To investigate the involvement of the potent insulinotropic hormones gastric inhibitory polypeptide (GIP) and truncated glucagon-like peptide-1 (tGLP-1) in the postprandial hyperinsulinaemia of obesity, we examined the changes in plasma levels of GIP and tGLP-1 by an oral glucose tolerance test (OGTT) in nine normal subjects (controls), nine obese subjects without glucose intolerance (Group A), and six obese mild diabetic patients (Group B). Following the OGTT, plasma GIP levels in Group B were increased more markedly than those in the other two groups. Plasma levels of tGLP-1 were estimated by the difference between the values measured with the N-terminal directed antiserum (GLP-1NT) and those with the C-terminal directed antiserum (GLP-1 CT). Plasma levels of GLP-1 NT were increased in Group B, but decreased in the other two groups. Plasma GLP-1 CT levels were increased in all groups with the highest response in Group B. These results suggest that the combined augmentation of plasma GIP and tGLP-1 responses were involved in the delayed and considerable increases in plasma insulin after glucose ingestion in obese diabetic patients. Since tGLP-1 is suppressed in the hyperglycaemic hyperinsulinaemic state in normal subjects, the augmented tGLP-1 response appears to be characteristic of obese Type 2 diabetes.
Gastric inhibitory polypeptide (tGIP) and truncated glucagon like peptide-1 (GLP-1) are potent gastrointestinal insulinotropic factors (incretin), are most released after a meal or ingestion of glucose in man and animals. To investigate whether sulfonylurea (SU) affects the secretion of incretin, the modulation of plasma GIP and tGLP-1 levels following glucose ingestion in non-insulin-dependent diabetic type 2 patients with or without SU therapy was studied. A 75-G oral glucose tolerance test (OGTT) was carried out on 9 healthy subjects (controls) and 18 patients with non-obese type 2, 9 of whom were treated by diet alone (NIDDM-diet) and the other 9 with SU (glibenclamide 2.5 mg or gliclazide 40 mg) once a day (NIDDM-SU). Plasma GIP was measured by radioimmunoassay (RIA) with R65 antibody, and GLP-1 was measured by RIA with N-terminal-directed antiserum R1043 (GLP-1NT) and C-terminal-directed antiserum R2337 (GLP-1CT). Following OGTT, plasma glucose, GIP, GLP-1NT, and GLP-1CT in type 2 patients increased more markedly than in controls, despite the lower response of insulin. However, there were no significant differences in plasma levels of these peptides between the NIDDM-diet and NIDDM-SU groups. Therefore, it is unlikely that SU is involved in the high response of GIP and GLP-1s to OGTT in type 2 patients.
Genomic DNA from a patient with acute intermittent porphyria were analyzed by the polymerase chain reaction (PCR)-direct sequencing method. The patient was heterozygote for a point mutation G to C at the last position of exon 12 of the porphobilinogen deaminase (PBG-D) gene. Analysis of the cDNA fragments amplified by PCR revealed that the patient has the abnormal PBG-D mRNA, which does not have exon 12 and exists in an approximately equal amount to the normal mRNA.
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