RESEARCH DESIGN AND METHODSâ GLP-1 (25 nmol) was injected subcutaneously into either the abdominal wall or the gluteal region at a standardized.
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A R T I C L E
Subcutaneous Injection of the Incretin Hormone Glucagon-Like Peptide 1 Abolishes Postprandial Glycemia in NIDDM MARK K. GUTNIAK, MD, PHD BlRGITTA LlNDE, MD, PHD
JENS J. HOLST, MD, PHD SUAD EFENDIC, MD, PHD
OBJECTIVE — To investigate the effect of subcutaneously injected glucagon-like peptide 1 (GLP-1) (7-36)amide on postprandial plasma glucose, insulin, and Cpeptide levels in patients with non-insulin-dependent diabetes mellitus (NIDDM) and a secondary failure to sulfonylureas.
RESEARCH DESIGN AND METHODS— GLP-1 (25 nmol) was injected subcutaneously into either the abdominal wall or the gluteal region at a standardized depth and speed. The injection device was guided by the ultrasound determination of the depth of the fat layer. The peptide was given 5 min before a standard meal. Plasma concentrations of glucose, C-peptide, insulin, glucagon, and GLP-1 were followed during 240 min after the injection. RESULTS — In control experiments, a significant hyperglycemia was attained after the meal. GLP-1 given into the abdominal wall not only virtually abolished the postprandial blood glucose rise but significantly decreased glucose concentrations, with a nadir at ~25 min after the injection. A rapid rise of C-peptide and insulin levels was observed 10-15 min after the injection of GLP-1. The stimulatory effect of GLP-1 was transient, and, at 45 min after the meal, both insulin and C-peptide levels were almost identical in GLP-1 and control experiments. Significantly lower glucagon concentrations were observed 35-65 min after the peptide injection. GLP-1 concentration in plasma increased from 10 pM to a peak concentration (Cmax) of 70 pM at Tmax 30 min after injection. Then GLP-1 levels rapidly decreased to 25 pM at 95 min and returned to basal at 215 min. The gluteal injection of GLP-1 had similar effects compared with the abdominal administration on plasma levels of glucose, insulin, C-peptide, and glucagon. CONCLUSIONS— GLP-1 is promptly absorbed from the subcutaneous tissue. It exerts a significant blood glucose lowering effect when administered before meals in overweight patients with NIDDM. From the Departments of Endocrinology (M.K.G., S.E.) and Clinical Physiology (B.L.), Karolinska Institute, Stockholm, Sweden; and the Department of Medical Physiology Q.J.H.), PANUM Institute, University of Copenhagen, Denmark. Address correspondence and reprint requests to Mark Gutniak, MD, PhD, Department of Endocrinology and Diabetology, Karolinska Institute, 104 01 Stockholm, Sweden. Received for publication 22 December 1993 and accepted in revised form 28 April 1994. GLP-1, glucagon-like peptide 1; NIDDM, non-insulin-dependent diabetes mellitus; RIA, radioimmunoassay; CV, coefficient of variation; AUC, area under the curve.
DIABETES CARE, VOLUME 17,
NUMBER 9,
SEPTEMBER
1994
G
lucagon-like peptide 1 (GLP-1) (736)amide is a gastrointestinal hormone processed from the proglucagon gene. This peptide is an important incretin (1-3). When infused before a meal in patients with non-insulin-dependent diabetes mellitus (NIDDM), GLP-1 exerted a significant antidiabetogenic effect as reflected by a decreased insulin requirement and decreased postprandial hyperglycemia (3-6). A significant glucoselowering effect was also observed when GLP-1 was given during fasting conditions (1,5). In both these experiments, the peptide was administered as a continuous intravenous infusion, and plasma levels of the hormone were approximately doubled. It is not clear whether the antidiabetogenic effect of the peptide is preserved during long-term administration or if the patients develop tachyphylaxis. Another important question is whether GLP-1 retains its effects after subcutaneous administration, which is almost a prerequisite for long-term therapy with the peptide. Therefore, in this study, we injected GLP-1 subcutaneously into the abdominal regions of NIDDM patients before a meal and evaluated absorption kinetics as well as glucose and hormonal responses. In an attempt to retard the absorption of the subcutaneously injected GLP-1, we also tried the gluteal region as an injection site.
RESEARCH DESIGN AND METHODS — The study protocol was approved by the ethics committee of the Karolinska Hospital. Eight overweight NIDDM patients (3 women, 5 men) with a secondary failure to sulfonylureas participated in the study (57 ± 7 years of age, body mass index 28.0 ± 1.5 kg/nT\ diabetes duration 10 ± 2 years, HbAu. 8.1 ± 0.3%). The patients fulfilled the criteria for NIDDM according to the National Diabetes Data Group (7). A standard diet was recommended with restrictions on simple carbohydrates. The patients were instructed to maintain this diet at least ?. weeks before and during the study. All patients were treated with in-
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Subcutaneous administration ofGLP-1
sulin. Injections of NPH insulin were interrupted 24 h before the experiment, and blood glucose was controlled by subcutaneously injected regular insulin. The last insulin dose was given before dinner the day before the experiment. All subjects were studied after an overnight fast. At 0730 on the morning of the study, a cannula (2 Venflon, Viggo, Helsingborg, Sweden) was placed into an antecubital vein and was used to sample blood intermittently. It was flushed with saline after each sampling. The depth of the subcutaneous fat layer in the injection area was measured with two-dimensional ultrasound using a linear scanner (7 MHz; ACUSON XP10, Mountain View, CA). The experiments were performed randomly on three separate occasions. Two to three weeks elapsed between the experiments. Twenty-five nanomoles (0.3 ml) of GLP-1 (Peninsula, St. Helens, Merseyside, England) was injected subcutaneously into the abdominal wall (~100 mm lateral to the umbilicus) or into the gluteal region (~100 mm dorsal to the iliac spine). In control experiments, saline was injected. The injections were given 5 min before a standard lunch (time 0), which they ate within 15 min while sitting in the bed. The meal consisted of boiled potatoes, boiled beef, cooked carrots, a glass of milk containing 0.5% butterfat, and a slice of bread baked with a mixture of wheat and rye flours. In this lunch, containing 550 kcal, 28, 26, and 46% of the energy came from protein, fat, and carbohydrates, respectively. The glucose, insulin, C-peptide, and GLP-1 samples were collected at —30, —15, and 0 min. The sampling continued at 5-min intervals up to 30 min and at 10-min intervals up to 60 min. The samples were then taken at 30-min intervals up to 240 min. The glucagon samples were taken at —30, 0, 15, 30, 60, 90, 120, 150, 180, 210, and 240 mm. Assays Blood samples were collected in plastic tubes containing EDTA (0.048 ml, 0.34
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M) and immediately placed on ice. Samples were centrifuged at 4°C, and the plasma was frozen at — 20°C. Plasma glucose was measured with a glucose oxidase method (8). HbAlc was measured by isoelectric focusing (normal
