The influence of body weight, age and glucose tolerance on the relationship between GIP secretion and beta-cell...

The aim of the present study was to examine the association between insulin and gastric inhibitory polypetide (GIP) secretion in conditions characterized by insulin resistance, i.e. obesity, impaired glucose tolerance (IGT), non-insulin dependent diabetes mellitus (NIDDM) and aging. Obesity, IGT and aging were associated with an increased insulin/C-peptide response to a test meal. The GIP response to the test meal was 'blunted' in the obese subjects but normal in older subjects and patients with IGT, thereby refuting the hypothesis that GIP is involved in the hyperinsulinaemia of these conditions. In contrast, lean NIDDM subjects showed both a reduced insulin/C-peptide repsonse and a decreased GIP response to the test meal indicating that dysfunction of GIP secretion could be involved in the impaired beta-cell function in NIDDM. The data, therefore, suggest that hypersecretion of GIP does not contribute to hyperinsulinaemia and hyper-C-peptidaemia in insulin-resistant states. In contrast, hyposecretion of GIP may be involved in hypoinsulinaemia/hypo-C-peptidaemia observed in NIDDM.