Complete sequences of glucagon-like peptide-1 from human and pig small intestine

In the small intestine, proglucagon is processed into the previously characterized peptide "glicentin" (proglucagon (PG) 1-69) and two smaller peptides showing about 50% homology with glucagon: glucagon-like peptide-1 and -2. It was assumed that the sites of post-translational cleavage in the small intestine of the proglucagon precursor were determined by pairs of basic amino acid residues flanking the two peptides. Earlier studies have shown that synthetic glucagon-like peptide-1 (GLP-1) synthesized according to the proposed structure (proglucagon 71-108 or because residue 108 is Gly, 72-107 amide) had no physiological effects, whereas a truncated from of GLP-1, corresponding to proglucagon 78-107 amide, strongly stimulated insulin secretion and depressed glucagon secretion. To determine the amino acid sequence of the naturally occurring peptide we isolated GLP-1 from human small intestine by hydrophobic, gel permeation, and reverse-phase high performance liquid chromatography. By analysis of composition and sequence it was determined that the peptide corresponded to PG 78-107. By mass spectrometry the molecular mass was determined to be 3295, corresponding to PG 78-107 amide. Furthermore, mass spectrometry of the methyl-esterified peptide showed an increase in mass compatible with the presence of alpha-carboxyl amidation. Thus, the gut-derived insulinotrophic hormone GLP-1 is shown to be PG 78-107 amide.     

Characterization of high-affinity receptors for truncated glucagon-like peptide-1 in rat gastric glands

The truncated form of glucagon-like peptide-1 (TGLP-1, or proglucagon 78-108), secreted by the mammalian intestine, has potent pharmacological activities, stimulating insulin release and inhibiting gastric acid secretion. We have characterized high-affinity receptors for this peptide in rat isolated fundic glands. Scatchard analysis of binding studies using mono-125I-TGLP-1(7-36) amide as tracer showed a single class of binding site of Kd (4.4 +/- (SE) .08) x 10(-10) M, with a tissue concentration of 1.0 +/- 0.1 fmol sites/microgram DNA. Whole GLP-1 was approximately 700 times less potent in displacing tracer, while human GLP-2 and pancreatic glucagon produced no significant displacement at concentrations up to 10(-6) M. The data support a physiological role for TGLP-1 in the regulation of gastric acid secretion.     

Naturally occurring products of proglucagon 111-160 in the porcine and human small intestine

Recent studies have revealed that the glucagon gene is expressed in the mammalian intestine. Here it codes for "glicentin" (proglucagon 1-69) and a glucagon-like peptide, proglucagon 78-107, recently isolated from porcine intestine. We studied the fate of the remaining COOH-terminal part of proglucagon (proglucagon 111-160) using radioimmunoassays against proglucagon 111-123 and 126-160. Two peptides were isolated from acid ethanol extracts of porcine ileal mucosa and sequenced: one corresponding to proglucagon 126-158 and one probably corresponding to proglucagon 111-158. By comparing human and porcine proglucagon sequences, Ala117 is replaced by Thr, and Ile138, Ala144, Ile152 and Gln153 are replaced by Val, Thr, Leu, and His. By gel filtration and radioimmunoassay of intestinal extracts it was established that a large part of porcine and virtually all of human proglucagon are processed to release proglucagon 111-123 (designated spacer peptide 2), which, like proglucagon 126-158 must be considered a potential hormonal entity. By isocratic high pressure liquid chromatography human spacer peptide 2 was indistinguishable from synthetic proglucagon 111-122 amide, suggesting that this is the structure of the naturally occurring human peptide.     

Priming effect of glucagon-like peptide-1 (7-36) amide, glucose-dependent insulinotropic polypeptide and cholecystokinin-8 at the isolated perfused rat pancreas.

The priming effect of glucagon-like peptide-1 (7-36) amide (GLP-1 (7-36) amide), glucose-dependent insulin-releasing polypeptide (GIP) and cholecystokinin-8 (CCK-8) on glucose-induced insulin secretion from rat pancreas was investigated. The isolated pancreas was perfused in vitro with Krebs-Ringer bicarbonate buffer containing 2.8 mmol/l glucose. After 10 min this medium was supplemented with GLP-1 (7-36) amide, GIP or CCK-8 (10, 100, 1000 pmol/l) for 10 min. After an additional 10 min period with 2.8 mmol/l glucose alone, insulin secretion was stimulated with buffer containing 10 mmol/l glucose for 44 min. In control experiments the typical biphasic insulin response to 10 mmol/l glucose occurred. Pretreatment of the pancreas with GIP augmented insulin secretion: 10 pmol/l GIP enhanced only the first phase of the secretory response to 10 mmol/l glucose; 100 and 1000 pmol/l GIP stimulated both phases of hormone secretion. After exposure to CCK-8, enhanced insulin release during the first (at 10 and 1000 pmol/l CCK-8) and the second phase (at 1000 pmol/l) was observed. Priming with 100 pmol/l GLP-1 (7-36) amide significantly amplified the first and 1000 pmol/l GLP-1 (7-36) amide both secretion periods, 10 pmol/l GLP-1 (7-36) amide had no significant effect. All three peptide hormones influenced the first, quickly arising secretory response more than the second phase. Priming with forskolin (30 mM) enhanced the secretory response to 10 mM glucose plus 0.5 nM GLP-1 (7-36) amide 4-fold. With a glucose-responsive B-cell line (HIT cells), we investigated the hypothesis that the priming effect of GLP-1 (7-36) amide is mediated by the adenylate cyclase system. Priming with either IBMX (0.1 mM) or forskolin (2.5 microM) enhanced the insulin release after a consecutive glucose stimulation (5 mM). This effect was pronounced when GLP-1 (7-36) amide (100 pM) was added during glucose stimulation. Priming capacities of intestinal peptide hormones may be involved in the regulation of postprandial insulin release. The incretin action of these hormones can probably, at least in part, be explained by these effects. The priming effect of GLP-1 (7-36) amide is most likely mediated by the adenylate cyclase system.     

Truncated glucagon-like peptide I, an insulin-releasing hormone from the distal gut

By hydrophobic gel permeation and high pressure liquid chromatography we isolated from pig intestinal mucosa a peptide which corresponds to proglucagon 78-107 as suggested by chromatography and determination of its N-terminal sequence. Natural and synthetic proglucagon 78-107 dose dependently and potently increased insulin secretion from the isolated perfused pig pancreas. Proglucagon 78-107 also secreted by the small intestine may participate in the hormonal control of insulin secretion.     

Glucagon-like peptide-1 (7–36) amide as a novel neuropeptide

Although earlier studies indicated that GLP-1 (7-36) amide was an intestinal peptide with a potent effect on glucose-dependent insulin secretion, later on it was found that several biological effects of this peptide occur in the brain, rather than in peripheral tissues. Thus, proglucagon is expressed in pancreas, intestine, and brain, but post translational processing of the precursor yields different products in these organs, glucagon-like peptide-1 (7-36) amide being one of the forms produced in the brain. Also, GLP-1 receptor cDNA from human and rat brains has been cloned and sequenced, and the deduced amino acid sequences are the same as those found in pancreatic islets. Through these receptors, GLP-1 (7-36) amide from gut or brain sources induces its effects on the release of neurotransmitters from selective brain nuclei, the inhibition of gastric secretion and motility, the regulation of food and drink intake, thermoregulation, and arterial blood pressure. Central administration (icv) of GLP-1 (7-36) amide produces a marked reduction in food and water intake, and the colocalization of the GLP-1 receptor, GLUT-2, and glucokinase mRNAs in hypothalamic neurons involved in glucose sensing suggests that these cells may be involved in the transduction of signals needed to produce a state of fullness. In addition, GLP-1 (7-36) amide inhibits gastric acid secretion and gastric emptying, but these effects are not found in vagotomized subjects, suggesting a centrally mediated effect. Similar results have been found with the action of this peptide on arterial blood pressure and heart rate in rats. Synthesis of GLP-1 (7-36) amide and its own receptors in the brain together with its abovementioned central physiological effects imply that this peptide may be considered a neuropeptide. Also, the presence of GLP-1 (7-36) amide in the synaptosome fraction and its calcium-dependent release by potassium stimulation, suggest that the peptide may act as a neurotransmitter although further electrophysiological and ultrastructural studies are needed to confirm this possibility.     

VIP receptors in pig liver cells: binding characteristics and role in degradation

The physiological role of VIP in the liver is controversial. VIP receptors are present, but their function in the metabolic regulation is uncertain. The interaction of porcine VIP with isolated cells from pig liver was studied with respect to receptor-binding, degradation and glycogenolytic action. In this model, VIP and liver showed homology of animal species. 1. Receptor-binding was heterogenous with Kd values of 10(-9) mol/l and 4 X 10(-8) mol/l, and a total amount of binding sites of 7 X 10(-11) mol per 10(9) cells. The peptide specificity showed that porcine and chicken VIP were equally potent in inhibiting receptor-bound 125I-VIP; secretin was about 30 times less potent; glucagon and somatostatin were ineffective. 2. Receptor-bound 125I-VIP was degraded since about 70% was released as radioactivity not reacting with VIP-antiserum. 3. Glucose-release was not stimulated by VIP (10(-6) mol/l) whereas the rate was increased two-fold by glucagon (10(-6) mol/l). In conclusion, VIP receptors in pig liver cells are different from other tissues regarding peptide specificity. It is suggested that receptor-binding mediates degradation of VIP by pig liver rather than metabolic effects.     

Solubilization of active GLP-1 (7–36)amide receptors from RINm5F plasma membranes

Glucagon-like peptide-1 (7–36)amide (GLP-1 (7–36)amide) represents a physiologically important incretin in mammals including man. Receptors for GLP-1 (7–36)amide have been described in RINm5F cells. We have solubilized active GLP-1 (7–36)amide receptors from RINm5F cell membranes utilizing the detergents octyl-β-glucoside and CHAPS; Triton X-100 and Lubrol PX were ineffective. Binding of radiolabeled GLP-1(7–36)amide to the solubilized receptor was inhibited conentration-dependently by addition of unlabeled peptide. Scatchard analysis of binding data revealed a single class of binding sites with K_a= 0.26 ± 0.03 nM and B_max= 65.4 ± 21.24 fmol/mg of protein for the membrane-bound receptor and K_a= 22.54 ± 4.42 μM and B_max= 3.9 ± 0.79 pmol/mg of protein for the solubilized receptor. The binding of the radiolabel to the solubilized receptor was dependent both on the concentrations of mono- and divalent cations and the protein/detergent ratio in the incubation buffer. The membrane bound receptor is sensitive to guanine-nucleotides, however neither GTP-γ-S nor GDP-β-S affected binding or labeled peptide to solubilized receptor. These data indicate that the solubilized receptor may have lost association with its G-protein. In conclusion, the here presented protocol allows solubilization of the GLP-1(7–36)amide receptor in a functional state and opens up the possibility for further molecular characterization of the receptor protein.     

Structure, measurement, and secretion of human glucagon-like peptide-2

By using radioimmunoassays toward the cDNA-predicted amino acid sequence of human glucagon-like peptide-2, a peptide was isolated from extracts of human ileum. By mass spectrometry and Edman sequencing, this peptide was identified as human proglucagon 126-158. High-performance liquid chromatography analyses indicated that a similar immunoreactive peptide (iGLP-2) was present in human plasma. Human plasma concentrations of iGLP-2 were elevated 3- to 4-fold at 1 to 2 h after ingestion of 800 to 1200 kcal meals.     

The mechanism of action of vinblastine. Binding of [acetyl-3H]vinblastine to embryonic chick brain tubulin and tubulin from sea urchin sperm tail outer doublet microtubules.

Tritium-labeled viblastine, specific activity 107 Ci/mol, was prepared by acetylation of desacetylvinblastine with [3H]acetic anhydride, and has been employed in a study of vinblastine binding to tubulin. There are two high affinity vinblastine-binding sites per mole of embryonic chick brain tubulin (KA = 3-5 X 10(5) l./mol). Binding to these sites was rapid, and relatively independent of temperature between 37 and 0degreeC. Vincristin sulfate and desacetylvinblastine sulfate, two other active vinca alkaloid derivatives, competitively inhibited the binding of vinblastine. The inhibition constant for vincristine was 1.7 X 10(-5) M; and for desacetylvinblastine, 2 X 10(-5) M. The vinblastine binding activity of tubulin decayed upon aging, but this property was not studied in detail. Vinblastine did not depolymerize stable sea urchin sperm tail outer doublet microtubules, nor did it bind to these microtubules. However, tubulin solubilized from the B subfiber of the outer doublet microtubules possessed the two high affinity binding sites (KA = 1-3 X 105 l./mol). These data suggest that vinblastine destroys microtubules in cells primarily by inhibition of microtubule polymerization, and does not directly destroy preformed microtubules.     

Lipolytic action of glucagon-like peptides in isolated rat adipocytes.

The lipolytic effect of GLP-1(1-36)-amide, GLP-1(7-36) amide and GLP-2 [proglucagon(126-159)] has been studied in isolated rat adipocytes. Glycerol release and cyclic AMP content were measured after incubation of adipocytes with GLPs and results have been compared with those obtained in the presence of glucagon. GLP-1(7-36)-amide and GLP-1(1-36)-amide at 10(-8), 10(-7) and 10(-6) M concentrations activated glycerol release, the truncated peptide having a more potent effect. On the other hand, GLP-2 had no effect on glycerol release. Also, it has been found that 10(-6) M GLP-1(7-36)-amide increases cyclic AMP content in adipocytes and does not compete with glucagon binding. These results demonstrate that GLP-1(7-36)-amide has a lipolytic effect on isolated rat adipocytes through different receptors than glucagon.     

Oral administration of a fusion protein containing eight GLP-1 analogues produced in <Emphasis Type="Italic">Escherichia coli</Emphasis> BL21(DE3) in streptozotocin-induced diabetic rats

Glucagon-like peptide-1 (7-36) amide (GLP-1), a gut hormone released into the blood stream after feeding, can stimulate insulin secretion by potentiating the insulinotropic action of glucose. An expression vector pET-22bG8, encoding a fusion protein containing eight tandem repeat GLP-1 ([Ser(8), Gln(26), Asp(34)]-GLP-1) analogues, was constructed and transformed into the Escherichia coli BL21(DE3) strain over-expressing the His-tagged fusion protein under the IPTG promoter. SDS-PAGE and Western blot analysis demonstrated that the His-tagged GLP-1 fusion protein migrated as a single protein with a molecular weight of 32 kDa. Following chronic (10 days) oral administration (20 mg kg(-1) day(-1)) of the fusion protein to diabetic rats, serum glucose levels were significantly lowered from 26 +/- 2.5 to 7.9 +/- 1.4 mmol/l. Further studies are needed to evaluate the potential use for GLP-1 analogue short peptide in the treatment of diabetes mellitus.     

Distribution of proglucagon mRNA and GLP-1 in the brainstem of chicks

Glucagon-like peptide-1 (GLP-1), structurally similar to glucagon, synthesized from the precursor proglucagon, is a well known anorexigenic peptide in the brain of several animal species. However, there are no previous reports concerning GLP-1-containing neurons in the chick brain. The aim of the present study was to investigate the distribution of proglucagon mRNA and GLP-1-immunoreactive (GLI) perikarya in various regions of the chick brain. We detected proglucagon mRNA in the brainstem, and to a lesser extent in the telencephalon. In the brainstem, a study using immunohistochemistry revealed that GLI perikarya were present in the nucleus motorius nervi facialis pars dosalis, nucleus motoris dorsalis nervi vagi and nucleus tractus solitarii. Furthermore, we found that proglucagon mRNA expression in the brainstem decreased after 24 h fasting. The present findings support the idea that endogenous GLP-1 is involved in feeding behavior of chicks.     

Binding of pigment epithelium-derived factor (PEDF) to retinoblastoma cells and cerebellar granule neurons. Evidence for a PEDF receptor.

Pigment epithelium-derived factor (PEDF) has neuronal differentiation and survival activity on retinoblastoma and cerebellar granule (CG) cells. Here, we investigated the presence of PEDF receptors on retinoblastoma Y-79 and CG cells. PEDF radiolabeled with (l25)I remained biologically active and was used for radioligand binding analysis. The binding was saturable and specific to a single class of receptors on both cells and with similar affinities (K(d) = 1.7-3.6 nM, B(max) = 0.5-2.7 x 10(5) sites/Y-79 cell; and K(d) = 3.2 nM, B(max) = 1.1 x 10(3) sites/CG cell). A polyclonal antiserum to PEDF, previously shown to block the PEDF neurotrophic activity, prevented the (125)I-PEDF binding. We designed two peptides from a region previously shown to confer the neurotrophic property to human PEDF, synthetic peptides 34-mer (positions 44-77) and 44-mer (positions 78-121). Only peptide 44-mer competed for the binding to Y-79 cell receptors (EC(50) = 5 nM) and exhibited neuronal differentiating activity. PEDF affinity column chromatography of membrane proteins from both cell types revealed a PEDF-binding protein of approximately 80 kDa. These results are the first demonstration of a PEDF-binding protein with characteristics of a PEDF receptor and suggest that the region comprising amino acid positions 78-121 of PEDF might be involved in ligand-receptor interactions.     

Glucagon-Like Peptide-1 Receptor Ligand Interactions: Structural Cross Talk between Ligands and the Extracellular Domain

Activation of the glucagon-like peptide-1 receptor (GLP-1R) in pancreatic β-cells potentiates insulin production and is a current therapeutic target for the treatment of type 2 diabetes mellitus (T2DM). Like other class B G protein-coupled receptors (GPCRs), the GLP-1R contains an N-terminal extracellular ligand binding domain. N-terminal truncations on the peptide agonist generate antagonists capable of binding to the extracellular domain, but not capable of activating full length receptor. The main objective of this study was to use Hydrogen/deuterium exchange (HDX) to identify how the amide hydrogen bonding network of peptide ligands and the extracellular domain of GLP-1R (nGLP-1R) were altered by binding interactions and to then use this platform to validate direct binding events for putative GLP-1R small molecule ligands. The HDX studies presented here for two glucagon-like peptide-1 receptor (GLP-1R) peptide ligands indicates that the antagonist exendin-4_[9-39] is significantly destabilized in the presence of nonionic detergents as compared to the agonist exendin-4. Furthermore, HDX can detect stabilization of exendin-4 and exendin-4_[9-39] hydrogen bonding networks at the N-terminal helix [Val19 to Lys27] upon binding to the N-terminal extracellular domain of GLP-1R (nGLP-1R). In addition we show hydrogen bonding network stabilization on nGLP-1R in response to ligand binding, and validate direct binding events with the extracellular domain of the receptor for putative GLP-1R small molecule ligands.     

Cortisol production by dispersed guinea-pig adrenal cells; a specific, sensitive and reproducible response to ACTH....and its fragments

Naturally occurring steroids and peptide hormones, tested at supraphysiological concentrations, were without effect on basal and human (h) 1-39 ACTH (NIBSC code 74/555, 25 ng/l (5.5 X 10(-12) mol/l] stimulated cortisol production. Further, low concentrations of angiotensin II, N-pro-opiocortin (N terminal fragment 1-76) and gamma-MSH all of which have been reported to synergise with ACTH with regard to cortisol production, were without significant effect alone or in combination with ACTH over the range 2.2 X 10(-13) to 5.5 X 10(-12) mol/l. The activity of h 1-39 was compared with that of the ACTH related peptides 1-24, 1-18, 1-17, 1-16, 1-13-NH2 (alpha MSH), 1-10 and 4-10. The dose responses were parallel and the same maximal cortisol output was observed with all the peptides except the 1-10 fragment. Half maximal stimulation occurred at 3.1 X 10(-12) (1-24), 4.4 X 10(-12) (h 1-39), 1.5 X 10(-11) (1-39), 3.3 X 10(-10) (1-18), 5 X 10(-9) (1-13-NH2), 8 X 10(-9) (1-17), 2 X 10(-7) (1-16) and 1 X 10(-5) (4-10) mol/l respectively. Interference by the above ACTH-derived peptides in cortisol secretion by the cells in response to 5.5 X 10(-12) mol/l h 1-39 ACTH was minimal over the range 5.2 X 10(-12)-2.2 X 10(-6) mol/l. The sensitivity of the adrenal cells to h 1-39 ACTH was such that 2 ng/l (4.4 X 10(-13) mol/l) provoked cortisol secretion over the control (P less than 0.05, n = 17). The coefficient of variation within assay for each dose on the full standard curve (2.2 X 10(-13)-1.1 X 10(-10) mol/l) was less than 10% (n = 6). Half maximal stimulation was given by 14.5 ng/l (3.2 X 10(-12) mol/l). Between control and 1.1 X 10(-10) mol/l ACTH there was a 32 +/- 8 (mean +/- SD, n = 9) fold change in cortisol production.     

Identification and characterization of glucagon-like peptide-1 7-36 amide-binding sites in the rat brain and lung

High-affinity binding sites for glucagon-like peptide-1 7-36 amide (GLP-1 7-36 NH2) were identified in rat brain and lung membranes. Binding of [125I]GLP-1 7-36 NH2 was rapid, reversible, specific, saturable and pH dependent. Specific binding in the central nervous system was particularly high in the hypothalamus and the brain stem. Oxyntomodulin, glucagon-like peptide-1, glucagon-like peptide-2 and glucagon were 100-1000-fold less potent than GLP-1 7-36 NH2 in competition for this binding site.     

Degradation and glycemic effects of His(7)-glucitol glucagon-like peptide-1(7-36)amide in obese diabetic ob/ob mice

Glucagon-like peptide-1(7-36)amide (tGLP-1) has attracted considerable potential as a possible therapeutic agent for type 2 diabetes. However, tGLP-1 is rapidly inactivated in vivo by the exopeptidase dipeptidyl peptidase IV (DPP IV), thereby terminating its insulin releasing activity. The present study has examined the ability of a novel analogue, His(7)-glucitol tGLP-1 to resist plasma degradation and enhance the insulin-releasing and antihyperglycemic activity of the peptide in 20-25-week-old obese diabetic ob/ob mice. Degradation of native tGLP-1 by incubation at 37 degrees C with obese mouse plasma was clearly evident after 3 h (35% intact). After 6 h, more than 87% of tGLP-1 was converted to GLP-1(9-36)amide and two further N-terminal fragments, GLP-1(7-28) and GLP-1(9-28). In contrast, His(7)-glucitol tGLP-1 was completely resistant to N-terminal degradation. The formation of GLP-1(9-36)amide from native tGLP-1 was almost totally abolished by addition of diprotin A, a specific inhibitor of DPP IV. Effects of tGLP-1 and His(7)-glucitol tGLP-1 were examined in overnight fasted obese mice following i.p. injection of either peptide (30 nmol/kg) together with glucose (18 mmol/kg) or in association with feeding. Plasma glucose was significantly lower and insulin response greater following administration of His(7)-glucitol tGLP-1 as compared to glucose alone. Native tGLP-1 lacked antidiabetic effects under the conditions employed, and neither peptide influenced the glucose-lowering action of exogenous insulin (50 units/kg). Twice daily s.c. injection of ob/ob mice with His(7)-glucitol tGLP-1 (10 nmol/kg) for 7 days reduced fasting hyperglycemia and greatly augmented the plasma insulin response to the peptides given in association with feeding. These data demonstrate that His(7)-glucitol tGLP-1 displays resistance to plasma DPP IV degradation and exhibits antihyperglycemic activity and substantially enhanced insulin-releasing action in a commonly used animal model of type 2 diabetes.     

Enteral nutrients potentiate the intestinotrophic action of glucagon-like peptide-2 in association with increased insulin-like growth factor-I responses in rats

Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent, intestinotrophic hormone derived from posttranslational processing of proglucagon in the distal bowel. GLP-2 is thought to act through indirect mediators, such as IGF-I. We investigated whether intestinal expression of GLP-2 and IGF-I system components are increased with the mucosal growth induced by enteral nutrient (EN) and/or a low dose of GLP-2 in parenterally fed rats. Rats were randomized to four treatment groups using a 2 x 2 design and maintained with parenteral nutrition (PN) for 7 days: PN alone, EN, GLP-2, and EN+GLP-2; n = 7-9. The two main treatment effects are +/-GLP-2 (100 microg.kg body wt(-1).day(-1)) and +/-EN (43% of energy needs, days 4-6). Combination treatment with EN+GLP-2 induced synergistic intestinal growth in ileum, resulting in greater mucosal cellularity, sucrase segmental activity, and gain of body weight (ENxGLP-2, P < 0.04). In addition, EN+GLP-2 induced a significant 28% increase in plasma concentration of bioactive GLP-2, a significant 102% increase in ileal proglucagon mRNA with no change in ileal dipeptidyl peptidase-IV (DPP-IV) specific activity, and significantly reduced plasma DPP-IV activity compared with GLP-2. This indicates that EN potentiates the intestinotrophic action of GLP-2. Proliferation of enterocytes due to GLP-2 infusion was associated with greater expression of ileal proglucagon, GLP-2 receptor, IGF-I, IGF binding protein-3 mRNAs, and greater IGF-I peptide concentration in ileum (P < 0.032). Ileal IGF-I mRNA was positively correlated with expression of proglucagon, GLP-2R, and IGFBP-5 mRNAs (R2 = 0.43-0.56, P < 0.0001). Our findings support the hypothesis that IGF-I is one of the downstream mediators of GLP-2 action in a physiological model of intestinal growth.