title: Insulin modulates glucose-dependent insulinotropic polypeptide (GIP) secretion from enteroendocrine K cells in rats.
abstract: Effects of insulin excess and deficiency on glucose-dependent insulinotropic polypeptide (GIP) was examined in rats following insulinoma transplantation or streptozotocin (STZ) administration. Over 14 days, food intake was increased (p < 0.001) in both groups of rats, with decreased body weight (p < 0.01) in STZ rats. Non-fasting plasma glucose levels were decreased (p < 0.01) and plasma insulin levels increased (p < 0.001) in insulinoma-bearing rats, whereas STZ treatment elevated glucose (p < 0.001) and decreased insulin (p < 0.01). Circulating GIP concentrations were elevated (p < 0.01) in both animal models. At 14 days, oral glucose resulted in a decreased glycaemic excursion (p < 0.05) with concomitant elevations in insulin release (p < 0.001) in insulinoma-bearing rats, whereas STZ-treated rats displayed similar glucose-lowering effects but reduced insulin levels (p < 0.01). GIP concentrations were augmented in STZ rats (p < 0.05) following oral glucose. Plasma glucose and insulin concentrations were not affected by oral fat, but fat-induced GIP secretion was particularly (p < 0.05) increased in insulinoma-bearing rats. Exogenous GIP enhanced (p < 0.05) glucose-lowering in all groups of rats accompanied by insulin releasing (p < 0.001) effects in insulinoma-bearing and control rats. Both rat models exhibited increased (p < 0.001) intestinal weight but decreased intestinal GIP concentrations. These data suggest that circulating insulin has direct and indirect effects on the synthesis and secretion of GIP.
authors.affiliation: SAAD Centre for Pharmacy and Diabetes, School of Biomedical Sciences, University of Ulster, Coleraine, BT52 1SA, UK. n.irwin@ulster.ac.uk
authors.forename: Nigel
authors.initials: N
authors.lastname: Irwin
authors.forename: Jacqueline M E
authors.initials: JM
authors.lastname: Francis
authors.forename: Peter R
authors.initials: PR
authors.lastname: Flatt
mesh_terms: D000818:Animals; D001786:Blood Glucose; D001835:Body Weight; D019858:Enteroendocrine Cells / Q000378:metabolism*; D005223:Fats / Q000378:metabolism; D005749:Gastric Inhibitory Polypeptide / Q000097:blood / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000097:blood / Q000378:metabolism*; D007333:Insulin Resistance; D007340:Insulinoma / Q000097:blood / Q000139:chemically induced / Q000378:metabolism*; D008297:Male; D010190:Pancreatic Neoplasms / Q000097:blood / Q000139:chemically induced / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013311:Streptozocin
chemical_list: D001786:Blood Glucose; D005223:Fats; D007328:Insulin; D005749:Gastric Inhibitory Polypeptide; D013311:Streptozocin; D005947:Glucose