Background/Aims-Dietary fibre influence growth and function of the upper gastrointestinal tract. This study investigates the importance of dietary fibre in intestinal growth in experimental diabetes, and correlates intestinal growth with plasma levels of the intestinotrophic factor, glucagon-like peptide 2 (GLP-2). Methods-Male Wistar rats were randomised to the following groups: two streptozotocin-diabetic and two control groups fed either a fibre-containing or a fibre-free diet for three weeks. Intestinal weight, length, and morphometric data (villus height, villus area, crypt depth) were measured. Blood samples were obtained after two weeks for measurement of GLP-2 and enteroglucagon (glicentin, oxyntomodulin). Results-The mean daily consumption of food in the two diabetic groups was 40% higher than in controls. In diabetic rats fed fibre, the increase in intestinal weight from day 0 to 20 was sixfold greater than that of the controls and small intestine weight per cm length was increased by 50%. In the diabetic rats fed a fibre-free diet, intestinal growth was 30% less than in diabetic rats fed fibre, and intestinal weight increased only threefold compared with controls. Morphometric data showed that the intestinal increase in diabetic rats fed fibre was due primarily to growth of the mucosal layer. Villus height and crypt depth increased 60% and 40% respectively, but by only 20% in fibre-free diabetic rats. The plasma levels of GLP-2 parallelled diabetic intestinal growth, whereas plasma levels of enteroglucagon increased regardless of the extent of intestinal growth. Conclusions-Intestinal growth in experimental diabetes is strongly influenced by the presence of dietary fibre. The eVect may be mediated by GLP-2. (Gut 1999;45:672-678)

Aims/hypothesis Glucose-dependent insulinotropic polypeptide (GIP) has been proposed to exert insulin-independent effects on lipid and bone metabolism. We investigated the effect of a 6-day s.c. GIP infusion on circulating lipids, white adipose tissue (WAT), brown adipose tissue (BAT), hepatic fat content, inflammatory markers, respiratory exchange ratio (RER), and bone homeostasis in patients with type 1 diabetes. Methods In a randomized, placebo-controlled, double-blind, crossover study, 20 men with type 1 diabetes underwent a 6-day continuous s.c. infusion with GIP (6 pmol/kg/min) and placebo (saline), with an interposed 7-day washout period. Results During GIP infusion, participants (26 ± 8 years [mean ± SD]; BMI 23.8 ± 1.8 kg/m2; HbA1c 51 ± 10 mmol/mol [6.8 ± 3.1%]) experienced transiently increased circulating concentrations of NEFA (p = 0.0005), decreased RER (p = 0.009), indication of increased fatty acid β-oxidation, and decreased levels of the bone resorption marker C-terminal telopeptide (p = 0.000072) compared to placebo. After six days of GIP infusion, hepatic fat content was increased by 12.6% (p = 0.007) and supraclavicular skin temperature, a surrogate indicator of BAT activity, was increased by 0.29°C (p < 0.000001) compared to placebo. WAT transcriptomic profile as well as circulating lipid species, proteome, markers of inflammation, and bone homeostasis were unaffected. Conclusions/interpretation Six days s.c. GIP infusion in men with type 1 diabetes transiently decreased bone resorption and increased NEFA and β-oxidation. Further, hepatic fat content, and supraclavicular skin temperature were increased without affecting WAT transcriptomics, the circulating proteome, lipids, or inflammatory markers.

Glucose-dependent insulinotropic polypeptide (GIP) plays an important role in the glucose and lipid metabolism. We investigated the effects of exogenous GIP on lipid metabolism during time of stable insulin levels. Ten male patients with type 1 diabetes without endogenous insulin secretion (C-peptide-negative, mean [±SD] age 26 ± 4years, body mass index 24 [±2] kg/m 2 , glycated haemoglobin 56 [±8] mmol/mol or 7.3 [±0.8]%) were studied in a randomized, double-blind, placebo-controlled, crossover study with continuous intravenous infusions of GIP (4 pmol/kg/min) or placebo (saline), during two separate 90-minute hyperglycaemic (12 mmol/L) clamps with basal insulin substitution (0.1-0.2 mU/kg/min). Plasma glycerol concentrations increased from baseline during GIP infusion and decreased during placebo infusion (baselinesubtracted area under the curve [bsAUC] 703 ± 407 vs. À262 ± 240 μmol/L Â min, respectively; P < 0.001). Free fatty acids (FFAs) increased during GIP infusions (bsAUC 5505 ± 2170 μEq/L Â min) and remained unchanged during placebo infusion (bsAUC À74 ± 2363 μEq/L Â min), resulting in a significant difference between GIP and placebo infusions (P < 0.001). Plasma concentrations of glucose, insulin, glucagon-like peptide-1 and glucagon were similar during GIP and placebo infusions. GIP increased plasma glycerol and FFAs in patients with type 1 diabetes during hyperglycaemia and stable basal insulin levels. This supports a direct lipolytic effect of GIP at high glucose and low levels of plasma insulin.

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