| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
ARTICLES |
Diabetes Discovery (A.B.D., H.K.), Novo Nordisk A/S, Novo allé, Dk-2880 Bagsvaerd, Denmark; and Department of Physiology (A.M.J.B.), University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
Address all correspondence and requests for reprints to: Dr. Hans Kofod Diabetes Discovery, Novo Nordisk A/S, Novo allé, 6B3.99, Dk-2880 Bagsvaerd, Denmark. E-mail: HKO{at}novo.dk
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Glucose-dependent insulinotropic peptide (GIP) dose dependently stimulated the release of GLP-1 and resulted in a 2-fold increase at 100 nM GIP. This effect was fully inhibited by 10 nM somatostatin. However, neither basal or GIP stimulated GLP-1 secretion were affected by ambient glucose concentrations from 5–25 mM. The receptor-independent secretagogues ß phorbol myristate acetate and forskolin dose dependently increased the secretion of GLP-1; effects inhibited by staurosporine and H8 respectively. Costimulation with GIP and phorbol ester, but not forskolin, resulted in an additive response. Furthermore, the effect of GIP could be inhibited by H8 but not by staurosporine.
These results indicate that glucose does not directly stimulate canine L-cells. It is more probable that glucose releases GIP from the upper intestine that in turn stimulates GLP-1 secretion. The ability of GIP to stimulate GLP-1 secretion is probably mediated through activation of protein kinase A.
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
GLP-1 is a product of the posttranslational cleavage of the proglucagon peptide and the majority of the peptide is produced in the L-cells of the ileum and colon. However, GLP-1 is also expressed in the rectum, the pancreatic A cell, and the brain stem. Although, the cleavage of proglucagon results in several different forms of GLP-1, GLP-1 (7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36)amide has been reported to be the most abundant form secreted from the L-cell (for review see Refs. 7 and 8). In the present paper, GLP-1 (7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36) amide is referred to as GLP-1.
In humans, GLP-1 is released in response to glucose, protein and fat, with glucose being the most potent secretagogue (9). The stimulatory effect of glucose has also been observed in a number of animal models; perfused canine and porcine ileum (10, 11), cultured fetal rat intestinal cells (12), and perfused rat colon (13). Endocrine and neurocrine regulatory peptides also stimulate the secretion of GLP-1. Bombesin/gastrin releasing peptide and calcitonin gene related peptide have been shown to stimulate the release of GLP-1 (11, 14, 15, 16, 17).
In particular, GIP has been shown to be a potent stimulator of GLP-1 release (14, 16, 17). The early release of GLP-1 after oral glucose intake and the rapid stimulation of GIP by glucose, together with the anatomical location of GIP and GLP-1 producing cells has led to the suggestion of an intraintestinal stimulatory loop in the generation of the incretin effect (14, 15, 18). However, the models used for these studies are hampered by the presence of neurocrine, endocrine, and paracrine factors because these have all been performed in whole tissue or crude cell preparations.
In this paper, we address the question of whether glucose has a direct effect on GLP-1 secretion from the intestinal L-cell and examine the possible dependence on GIP. Furthermore, we have used receptor independent stimulants of second messengers together with GIP to gain insight in the intracellular signaling pathway activated by GIP in the L-cell. For this purpose, we have established a GLP-1 release assay based on an enriched canine L-cell preparation in short-term culture (19). By means of centrifugal-elutriation, we have separated a subpopulation from a crude preparation of dispersed cells achieved by collagenase/EDTA digestion of canine ileum. This experimental set-up allowed us to study more directly the regulation of GLP-1 secretion in a controlled system of primary canine L-cells.
|
Materials and Methods |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Cell isolation and culture
The dogs were anesthetized with sodium pentobarbital and the
ileum (40 cm of the distal small intestine) was removed. After surgery,
the dogs were killed with an overdose of sodium pentobarbital. The
intestine was rinsed in ice-cold HBSS (Gibco, Grand Island, NY) with
0.65 mM dithiothreitorl (DTT; Merck), BSA (Sigma Chemical
Co., St. Louis, MO) 1%, penicillin/streptomycin (Gibco) 10 ml/liter,
NaHCO3 (Merck, Darmstadt, Germany) 9.05 mM,
Hepes (Sigma) 20 mM (HBSS/DTT), and the mucosa was stripped
off the submucosa and minced. Aliquots of 10 g were digested with
collagenase (Sigma type 1) 75 U/ml in Basal Medium Eagle (Gibco)
including NaHCO3 26.4 mM, BSA 0.1%, and HEPES
10 mM, at pH 6.9 for 1 h in a 37 C shaking water bath.
In the last 15 min of the digest, ethyldiaminetetraacetic acid (EDTA;
Merck, 3 mM final concentration) was added. Dispersed cells
were separated, and the remaining tissue pieces were repeatedly
digested (four to five times) as described. The cells-suspension from
the first digest were discarded, and the cells from digests 2–4/5 were
pooled. The resulting cell suspension was washed three times in
ice-cold HBSS/DTT, filtered through 80 µm nylon filter (Nytal P80,
SST Thal, Thal, Switzerland) and diluted to 6 x 106
cells/ml in HBSS/DTT. Typically, 1000–2000 ml were obtained.
To determine peptide content, 1-ml samples were collected, centrifuged, and the pellet resuspended in 1 ml formic acid (Merck) 0.1%, boiled for 10 min, adjusted to pH 7 with NaOH (Merck), and stored at -20 C for later GLP-1 assay.
Enrichment of L-cells and removal of bacteria was achieved by
centrifugal elutriation using a four-chamber Curamé 3000
Elutriator (Heraeus, Osterode, Germany) (20, 21), cells were loaded and
eluted in HBSS/DTT. The cell suspension (100 ml) was loaded at 2600 rpm
with a flow-rate of 15 ml/l at room temperature. Small cells and
bacteria were removed by washing for 4 min at 2600 rpm and 6 min at
2000 rpm. Cells were collected in 50-ml fractions at the rpm indicated
in Fig. 1
. To determine the fractions
containing the majority of the GLP-1 producing cells, the cell
suspensions were centrifuged at 800 x g and the
pellets extracted as previously described.
|
). The cell suspension was
centrifuged at 800 x g and resuspended to 2 x
106 cells/ml in 47.5% DMEM (Gibco) and 47.5% Ham’s F-12
medium (Gibco) supplemented with 5% dog serum (obtained from blood
samples taken from the dogs before anesthesia), penicillin/streptomycin
10 ml/liter, hydrocortisone (Sigma) 1 µg/ml, insulin (Novo Nordisk) 4
ng/ml, nerve growth factor (Sigma) 5 ng/ml, and 11 mM
glucose (Pro Labo). Samples of cells before culture (0.5 ml) were
extracted for GLP-1 measurement. The remainder of the suspension was
plated at 0.5 ml/well onto 24 well-plates coated with rat tail collagen
type 1 (Sigma) and incubated for 36–48 h at 37 C, 5%
CO2.
Release experiments
After incubation, the unattached cells were removed by a wash in
DMEM including BSA 0.1% (DMEM/BSA) and preincubated for 2 h at 37
C, 5% CO2, in 0.5 ml DMEM/BSA, 5.5 mM glucose.
After preincubation, the medium was replaced with 450–475 µl
DMEM/BSA. Stock solutions of secretagogues (peptides, glucose, etc.)
were added in volumes of 25 µl from 20x stock solutions. The cells
were incubated for 2 h and the medium collected, centrifuged at
4000 x g, and supernatant kept at -20 C for
subsequent GLP-1 measurement. Cells in control wells (three per plate)
were only exposed to 5.5 mM glucose and referred to as
basal. After removal of the medium, cells attached to control wells
were lysed in 0.5 ml formic acid 0.1% and extracted as described
previously.
The results were calculated to present GLP-1 release as a percentage of the total GLP-1 in the cultured cells (%TCC). Subsequently, the %TCC were normalized to basal or, in case where inhibitors were used, the %TCC was normalized to maximal release.
The following secretagogues and inhibitors were used: porcine
glucose-dependent insulinotropic peptide (GIP), human calcitonin gene
regulated peptide (CGRP), bombesin (BBS), (human) gastrin releasing
peptide (all from Peninsula, Belmont, CA) and somatostatin-14 (SS-14;
Sigma) were all dissolved in 0.1% human serum albumin (ORHA 20/21,
Behring, Marburg, Germany) at a concentration of 2 x
10-6 M. Glucose (Merck) was diluted in
H2O to a concentration of 0.1 M,
N-(2-(methylamino)ethyl-5-isoquinolinesulfonamide
dihydrochloride (H8; Seikagaku Kogyo Co., Ltd., Tokyo, Japan), 2
x 10-6 M in H2O, Forskolin
(Sigma), 2 x 10-5 M in
H2O-ethanol 0.06%, staurosporine (Sigma), 2 x
10-5 M in H2O and dimethyl
sulfoxide (DMSO) 1:250, and 4ß-phorbol 12ß-myristate 13
-acetate
(PMA; Molecular Probes Europe BV, Leiden, The Netherlands), 8 x
10-5 M in H2O-DMSO 1:5.
GLP-1 measurement
A modification of the sensitive sandwich ELISA was used to
determinate of GLP-1 concentrations (22). Monoclonal mouse-Ab (F5A3;
Novo Nordisk, raised against GLP-1 (26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36)) was used as the substrate
antibody to coat the plates. Biotinylated polyclonal rabbit-Ab
[91022–2; J. J. Holst (University of Copenhagen, Copenhagen,
Denmark)] raised against GLP-1 (7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17) was used as the suspension
antibody. GLP-1 (7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37) (Novo Nordisk) was diluted in DMEM/BSA and used
as standard. A 80 µl sample was added to 20 µl suspension antibody
solution, corresponding to 2.4-µg antibody per well. Some samples
were diluted in DMEM/BSA. The ELISA has a working range from 10–500
pM.
Immunohistochemistry
Cells in controls wells were fixed in Bouin fixative, then
washed in PBS and preincubated in H2O2 and goat
serum for 30 min at room temperature. The cells were incubated
overnight with monoclonal antibodies against proglucagon (the proximal
part of glucagon, Dr. M. Gregor, Tubingen), Neurotensin (NT-C-5), GIP
(3.65H), Somatostatin (S10) (produced at the University of British
Columbia) and rabbit anti-5-HT (Dako, Glostrup, Denmark) and visualized
using a Histostain-sp kit from Zymed Laboratories Inc. (San Francisco,
CA). Mucin-producing cells were recognized by Alcian blue staining.
Analysis of data
All experiments were performed in duplicate or triplicate and
repeated three or four times, using cells from different dogs (n =
3 or 4). The ELISA measurements were performed in duplicate, and data
are shown as the mean ± SEM. Significance was
analyzed using ANOVA; two-factor (Microsoft Excel). Difference were
considered significant at P < 0.05.
|
Results |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
. The window between 2000 rpm and 1700 rpm contained
approximately 70% of all GLP-1. The experiment was performed twice
with similar results. Therefore, the cells collected in the window
between 2000 rpm and 1700 rpm were used for the release experiments.
The recovery of cells was between 5 and 10% of the total cells in the
initial suspension. After elutriation, incubation, and release experiments, cells in control wells were lysed and total GLP-1 measured. Generally, the total amount of GLP-1 was from 200-1000 fmol/well, and basal release of GLP-1 was 10–20 fmol/well over the 2-h experimental period, corresponding to 2–5% TCC. The TCC, calculated as total content of GLP-1, did not change for any agents tested as compared with basal condition. Furthermore, no change was observed for all of the 24 wells as compared with the three used for controls.
Immunocytochemistry was regularly performed (Fig. 2 and 3) on
elutriated cells after 36-h culture using antibodies against
proglucagon, neurotensin, GIP, somatostatin, and 5-HT. For detection of
L-cells, we used a mouse-antibody, raised against the proglucagon (the
proximal part of Glucagon). This antibody stains all N-terminal
glucagon containing peptides (proglucagon, glicentin, oxyntomodulin,
and glucagon). Both proglucagon, glicentin, and oxyntomodulin is
present in the L-cell (for review see Ref.8). Therefore, this antibody
will costain with GLP-1 specific antibodies applied for
immuno-cytochemistry and histochemistry on cells and tissue-samples
from the small intestine. Whereas 5HT, somatostatin, and GIP
immunoreactivity were only rarely seen (1 or 2 per well), the
neurotensin immunoreactive cells accounted for approximately 30% of
total cells and the proglucagon immunoreactive cells accounted for
approximately 20–25% of total cells. Furthermore, we stained
mucin-containing cells with Alcian blue. These cells accounted for
approximately 40% of total cells.
|
|
0.05) at 5.5 mM
glucose, 206 ± 20% (P 0.05) at 11
mM glucose, and 266 ± 35% (P
0.05) at 25 mM glucose all compared with basal at 5.5
mM glucose (n = 4). For 5.5 mM and 25
mM glucose, the effect of 10 nM GIP was also
observed to be significant, whereas for 11 mM the variance
was too large. No significant difference between the three
dose-response curves was observed (Fig. 4). The osmolarity of the medium in the
presence of 25 mM glucose was 240 mosm.
|
0.05) as compared with the effect of GIP alone (n = 4) (Fig. 5).
|
0.001) of basal (n = 3) (Fig. 6). Both CGRP and GRP had no significant
effect on GLP-1 release (Fig. 6).
|
PKC was stimulated by PMA, 0.4–400 nM, which resulted in a
dose-dependent increase in GLP-1 release. The stimulation was 475
± 72% (P 0.01) increase at 400 nM PMA
as compared with basal. This effect was inhibited by staurosporin,
a PKC inhibitor. At 400 nM PMA, 1 µM
staurosporin reduced the effect to 50 ± 11% (P
0.01) (n = 3) as compared with the effect of PMA alone (Fig. 7A). The solvent DMSO did not exceed
0.01% of the total volume and did not show any effect on basal
secretion.
|
0.001, n = 3).
Staurosporine (1 µM) did not alter the effect of 100
nM GIP alone; however the GLP-1 release when both GIP and
PMA was present, was reduced to 133 ± 10%, normalized to GIP
alone (P 0.05, n = 3), equivalent to GIP alone
(Fig. 7B).
Forskolin, an adenylyl cyclase activator, was used to stimulate PKA.
The presence of forskolin, 1 nM to 1 µM,
caused a concentration-dependent increase in GLP-1 release. Maximal
release at 100 nM forskolin was 332 ± 76% of basal
(P 0.05). The PKA inhibitor H8 (100 nM)
reduced the response of forskolin (100 nM). As compared
with the effect of forskolin alone, H8 + forskolin reduced the GLP-1
release to 64 ± 9% (normalized to the effect of forskolin alone,
P 0.01, n = 3) (Fig. 8A). The solvent ethanol did not exceeded
0.003% of the total volume and did not show any effect on basal
secretion.
|
0.01). The inhibitory
effect of 100 nM H8 was also observed when both GIP and
forskolin were present and resulted in a GLP-1 release at 76 ±
9% (P 0.05) as compared with GIP alone (n = 3)
(Fig. 8B). Compared with the effect of GIP + forskolin, H8 reduced the
effect of GLP-1 release to 74 ± 1% (P
0.001). |
Discussion |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
In an attempt to circumvent these problems, cell lines expressing proglucagon have been used (24), but these introduce a different set of problems when attempting to extrapolate from cell lines to normal endocrine cells. Discrepancies between the GLP-1 secretion pattern observed in cell lines and primary cells has been reported. For example, carbachol has been shown to induce GLP-1 release from the STC-1 cell line (24), whereas in primary canine L-cell enriched cultures, epinephrine induced GLP-1 release was inhibited by carbachol (19).
Experiments in humans and animal models as well as experiments on tissue and cell preparations suggest that glucose directly stimulates GLP-1 secretion (10, 11, 13, 18, 23). However, the presence of 5–25 mM glucose in the absence of added signal peptides did not cause any increase in GLP-1 from our L-cell preparation (20–25% L-cells). The concentrations of glucose used were chosen to replicate the physiological range observed in canine blood. Resting blood glucose in dogs used to provide the cell cultures was between 4 and 5 mM, and the maximal physiological glucose concentration and osmolarity in the distal region of the small intestine was expected to be approximately 25 mM and 250 mosM (25).
The absence of a glucose effect on GLP-1 secretion from L-cells has previously been observed in rat intestine and in rat intestinal monolayer-culture (26, 12). This observation has been contradicted by data arising from experiments on perfused rat ileum and infusion studies of rat ileum with glucose at high concentration (27, 18). This effect was also observed to be sodium-dependent (28). However, it can be questioned whether these glucose concentrations (278 mM) used for the perfusion studies will ever reach the lower small intestine (25) in the dog and influence the GLP1 release. For this reason, we used only moderate raised glucose-concentrations. The observation that perfusion of rat duodenum with fat results in an increased immunoreactive GLP-1 secretion led to the suggestion of a doudenal-ileal factor, as only a minor population of L-cells is located in the duodenum. Further studies on perfused rat intestine revealed that GIP was released in response to fat in duodenum and that GIP was able to stimulate the secretion of GLP-1; thus, GIP was a candidate for the doudenal-ileal factor (14, 15, 18). However, the potency of GIP at physiological concentration has been debated (16). It has further been reported that K-cell-enriched cultured canine endocrine cells increased the secretion of GIP in response to glucose (29).
We have performed release experiments in the presence of GIP 0.01 nM to 100 nM and observed a dose-dependent secretion of GLP-1 with a significant effect of 10 nM and a 2-fold stimulation at maximum GIP. It has previously been shown that, in dog, oral glucose induces GIP release in vivo to reach a concentration at 1.5 ng/ml immunoreactive GIP, corresponding to approximately 300 pM (30). The latter is approximately 30 times less than the minimum required for significant effect of GIP in our system. The difference is probably explained by the difference between the in vivo situation where GIP can work in concert with intrinsic ennervation that increases the sensitivity and the in vitro system, where the L-cells are removed from their natural surroundings.
These findings support the hypothesis of a doudenal-ileal endocrine pathway in the overall incretin mechanism, where glucose stimulates GIP secretion, and thereafter GIP stimulates the release of GLP-1. However, because our cell preparation was not a pure culture of L-cells but consisted of several different intestinal cells, it is possible that unknown factors released from some of these cells in a glucose-dependent manner, may have an inhibitory effect upon GLP-1 release. It has recently been reported that in perfused rat small intestine, 10 nM GIP stimulate GLP-1 secretion, whereas in perfused canine ileum the same quantity of GIP failed show the same effect (31). Furthermore, previously reported data based on a hyperglycaemic clamp in normal human subjects showed that iv infusion of GIP failed to increase serum GLP-1. In a similar experiment, the insulin response was more sensitive to iv infusion of GLP-1 than GIP (32). Taken together, although GIP may play a role in a doudenal-ileal endocrine loop, it is unlikely to be the only factor that stimulates the release of GLP-1. Other elements such as a neural component may prove important for the incretin effect.
It was previously reported that the secretion of immunoreactive GLP-1 in rat was inhibited by somatostatin (SS-14 and SS-28) (14). Here we report that the effect of 100 nM GIP was dose dependently inhibited by somatostatin 14 and at 10 nM, GIP stimulated GLP-1 secretion returned to basal level. This observation augments the case for the effect of GIP being mediated through a specific receptor.
We also tested the effects of three other peptides: BBS, CGRP, and GRP in our system. All of these peptides have been reported to stimulate the secretion of GLP-1 (11, 14, 15, 16, 17). GLP-1 release was elevated significantly (but to a much lesser extent than with GIP) in the presence of 100 nM BBS. Surprisingly, GRP did not show the same effect, although the GLP-1 release tended to increase at 100 nM. Because of the homology between the two peptides, it was expected that the effect of the peptides would be identical. In the STC-1 cell-line, GRP is reported to induce the expression of proglucagon after 8 h (33). The short incubation time used in our studies suggests an effect on gene transcription is unlikely.
The results we obtain using GIP, BBS, CGRP, and GRP are somewhat in contrast to previously reported data. In vitro experiments using a rat intestinal cell preparation is was found that GLP-1 secretion were significant elevated by 0.1 nM GIP, 1 pM BBS, 1 pM GRP, and 10 nM (14). Furthermore, results obtained perfused rat colon revealed that 0.5 nM GIP, 10 nM BBS and 50 nM CGRP all significant increased the release of GLP-1 (15). These data imply that differences between species related to the response and sensitivity, of these secretagogues related to GLP-1 release. This argumentation is further supported by the earlier mentioned discrepancy in response to muscarinic agonists, which stimulate GLP-1 release in rat and mouse cells but have an inhibitory effect in dog (14, 19, 24).
Although GLP-1 release from L-cells in response to GIP has been documented (14, 15, 16, 17), the signal transduction mechanism involved is unknown. GIP has been shown to activate adenylyl cyclase in isolated rat islets (34), in CHO-K1 cells transfected with GIP receptors (35) and in HIT-cells (36). In Rin-cells GIP increased cAMP in a dose-dependent manner (37). Besides increasing the intracellular cAMP concentration, GIP also appears to increase the intracellular Ca++ levels in HIT-cells (36) and in mouse islets (38).
PMA, a potent PKC activator, has been reported to stimulate GLP-1 secretion from rat intestinal monolayers (39) and from the STC-1 cells (24). In our system, PMA stimulated GLP-1 release in a dose-dependent manner in the range of 0.4–400 nM. This effect was inhibited by the presence of 1 µM staurosporine, a PKC inhibitor. The inhibition was specifically related to the effect of PMA because the basal level of GLP-1 release was unaffected by staurosporine. Our data showed that GIP and PMA result in an additive response and because staurosporine did not affect GIP-stimulated GLP1 release, these data suggest that the PKC-dependent pathway is not involved in the intracellular signaling of GIP.
Forskolin stimulates adenylyl cyclase and causes an increased level of cAMP that in turn will stimulate PKA. It has been reported that forskolin can stimulate the release of GLP-1 in dog (19) and in the STC-1 cell line (24). We observed a dose-dependent increase of GLP-1 release in presence forskolin, and this effect was inhibited by H8 indicating the involvement of PKA. Addition of H8 reduced the effect of GIP alone and GIP plus forskolin. In addition, costimulation with GIP and forskolin did not result in an additive response. These data indicate that GIP stimulated GLP-1 release at least in part by activation of PKA.
In conclusion, we report that GIP stimulates the secretion of GLP-1 from canine L-cells and that neither basal or GIP stimulated GLP-1 secretion is influenced by physiological concentrations of glucose. The effect of GIP was inhibited by the presence of somatostatin. Bombesin stimulated the release of GLP-1, but neither GRP or CGRP had any significant effect on the GLP-1 release. The activation of both PKC and PKA lead to a stimulation of GLP-1 release, but only the latter is involved in the intracellular signaling of GIP related to the stimulation of GLP-1 release.
Received September 24, 1997.
|
References |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
This article has been cited by other articles:
 |
|
 |
|
  A. E. Relling and C. K. Reynolds Feeding Rumen-Inert Fats Differing in Their Degree of Saturation Decreases Intake and Increases Plasma Concentrations of Gut Peptides in Lactating Dairy Cows J Dairy Sci, March 1, 2007; 90(3): 1506 - 1515. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. E. Lim and P. L. Brubaker Glucagon-Like Peptide 1 Secretion by the L-Cell: The View From Within Diabetes, December 1, 2006; 55(Supplement_2): S70 - S77. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 F Reimann, M Maziarz, G Flock, A. M Habib, D. J Drucker, and F. M Gribble Characterization and functional role of voltage gated cation conductances in the glucagon-like peptide-1 secreting GLUTag cell line J. Physiol., February 15, 2005; 563(1): 161 - 175. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
F. Reimann and F. M. Gribble Glucose-Sensing in Glucagon-Like Peptide-1-Secreting Cells Diabetes, September 1, 2002; 51(9): 2757 - 2763. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. S. Rocca, J. LaGreca, J. Kalitsky, and P. L. Brubaker Monounsaturated Fatty Acid Diets Improve Glycemic Tolerance through Increased Secretion of Glucagon-Like Peptide-1 Endocrinology, March 1, 2001; 142(3): 1148 - 1155. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. Hansen, B. Hartmann, T. Bisgaard, H. Mineo, P. N. Jorgensen, and J. J. Holst Somatostatin restrains the secretion of glucagon-like peptide-1 and -2 from isolated perfused porcine ileum Am J Physiol Endocrinol Metab, June 1, 2000; 278(6): E1010 - E1018. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. Miyawaki, Y. Yamada, H. Yano, H. Niwa, N. Ban, Y. Ihara, A. Kubota, S. Fujimoto, M. Kajikawa, A. Kuroe, et al. Glucose intolerance caused by a defect in the entero-insular axis: A study in gastric inhibitory polypeptide receptor knockout mice PNAS, December 21, 1999; 96(26): 14843 - 14847. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. J. Kieffer and J. Francis Habener The Glucagon-Like Peptides Endocr. Rev., December 1, 1999; 20(6): 876 - 913. [Abstract] [Full Text]
|
|
|
|
 |
|
 A. M. J. Buchan Nutrient Tasting and Signaling Mechanisms in the Gut. III. Endocrine cell recognition of luminal nutrients Am J Physiol Gastrointest Liver Physiol, December 1, 1999; 277(6): G1103 - G1107. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. B. Damholt, A. M. J. Buchan, J. J. Holst, and H. Kofod Proglucagon Processing Profile in Canine L Cells Expressing Endogenous Prohormone Convertase 1/3 and Prohormone Convertase 2 Endocrinology, October 1, 1999; 140(10): 4800 - 4808. [Abstract] [Full Text]
|
|
|
|
|
|
C.-C. Tseng, X.-Y. Zhang, and M. M. Wolfe Effect of GIP and GLP-1 antagonists on insulin release in the rat Am J Physiol Endocrinol Metab, June 1, 1999; 276(6): E1049 - E1054. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Endocrinology | Endocrine Reviews | J. Clin. End. & Metab. |
| Molecular Endocrinology |
, P 
