Effect of ageing and diabetes on glucose‐dependent insulinotropic polypeptide and dipeptidyl peptidase IV responses to oral glucose

Summary Aims Glucose‐dependent insulinotropic polypeptide (GIP) acts on the pancreas to potentiate glucose‐induced insulin secretion (enteroinsular axis). GIP is rapidly inactivated in vivo by the enzyme dipeptidyl dipeptidase IV (DPP‐IV). The current studies were designed to examine the effect of ageing, obesity and diabetes on GIP and DPP‐IV responses to oral glucose. Methods Healthy controls (nine middle‐aged, age 42 ± 2 years, body mass index (BMI) 33 ± 1 kg/m2; nine elderly, age 71 ± 1 years, BMI 30 ± 1 kg/m2) and patients with Type 2 diabetes (12 middle‐aged, age 44 ± 2 years, BMI 34 ± 2 kg/m2; 19 elderly, age 74 ± 1 years, BMI 31 ± 1 kg/m2) underwent a 3‐h oral glucose tolerance test (OGTT) (glucose dose 40 g/m2). Results Insulin responses were similar in elderly controls and patients with diabetes, but were lower in middle‐aged patients with diabetes than in controls (308 ± 65 vs. 640 ± 109 p M, P < 0.05). GIP responses were similar in controls and patients with diabetes in each age group, but were higher in elderly controls (middle‐aged 45 ± 13; elderly 112 ± 13 p M, P < 0.01) and patients with diabetes (middle‐aged 55 ± 10; elderly 99 ± 10 p M, P <