Exercise Physiology and Metabolism Laboratory, Department of Kinesiology and Health Education, University of Texas at Austin, Austin, Texas 78712
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ABSTRACT |
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The effects of amylin
on fiber type-specific muscle glucose metabolism under hyperglycemic
(10 mmol/l) and hyperinsulinemic (2.1 nmol/l) conditions were
investigated using a rat hindlimb perfusion system. Amylin
concentration ranged from 1 to 100 nM. Efficacy for inhibition of
glucose uptake traced with 2-deoxyglucose by amylin was demonstrated in
all three fiber types. The incorporation of
2-deoxy-[3H]glucose
tracer decreased from control values by 41% in fast oxidative (FO),
36% in fast glycolytic (FG), and 37% in slow oxidative (SO)
muscle with 100 nM amylin. Amylin increased intracellular glucose 6-phosphate (G-6-P), and
G-6-P was negatively correlated with
2-deoxyglucose uptake in both FO (r = 0.65; P < 0.01) and FG
(r =
0.53;
P < 0.01) muscle. Muscle
glycogen concentration increased under control conditions and decreased
in the presence of 100 nM amylin. Lactate arteriovenous efflux across
the hindlimb increased significantly above control with 100 nM amylin
(5.03 ± 0.81 to 11.28 ± 0.94 µmol · g
1 · h
1).
Adenosine 3',5'cyclic monophosphate (cAMP) increased in
FO and FG muscle with amylin. Salmon calcitonin-(8
32), an amylin antagonist, ameliorated the effect of amylin on all responses other
than 2-deoxyglucose uptake and G-6-P
concentration. These results suggest that amylin may work through at
least two independent mechanisms, a cAMP-mediated effect on glycogen
metabolism and a non-cAMP-mediated inhibition of glycolysis.
skeletal muscle; glucose uptake; glucose 6-phosphate; glycogen
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INTRODUCTION |
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AMYLIN, a 37-amino acid peptide, is cosecreted with
insulin from the pancreatic -cells (10). It was originally isolated from amyloid plaque formations in type II diabetics and has been shown
to inhibit insulin-mediated glucose uptake and disposal in muscle and
to raise blood lactate (4, 26). Although the actual role of amylin is
unclear, it has been suggested that amylin agonists may be helpful in
preventing hyperinsulinemic shock in insulin-dependent diabetes
mellitus and that amylin antagonists, such as salmon calcitonin-(8
32)
[SCT-(8-32)], may be useful in increasing blood glucose
uptake into muscle in the non-insulin-dependent diabetes mellitus
(NIDDM) patient (26, 29, 31).
The mechanism of amylin action on skeletal muscle is still not completely understood (26). Amylin appears to inhibit glucose uptake by inhibiting glycogen synthesis and stimulating glycogenolysis possibly through an adenosine 3',5'-cyclic monophosphate (cAMP)-mediated mechanism (5, 16, 18, 23, 33). This may limit glucose uptake by increasing intracellular glucose 6-phosphate (G-6-P) levels, which could cause an inhibition of hexokinase resulting in a decrease in both glucose phosphorylation and net retention of transported glucose. It is unclear whether the inhibition of glycogen synthesis or activation of glycogen breakdown is primarily responsible for amylin action (5, 7, 17, 19, 33). Studies have also conflicted on whether a cAMP-mediated second messenger is responsible for amylin action and whether this mechanism is fiber type specific (5, 16, 23).
The purpose of this study was to test the efficacy and mechanism of
amylin action across the basic fiber types of skeletal muscle. In
addition, the efficacy of the SCT-(832) fragment as an amylin
antagonist was tested. Almost all studies on amylin action to date have
been conducted in vivo or with isolated muscle preparations. In most of
the isolated muscle studies the rat soleus muscle was used. However,
the soleus contains 80-90% slow oxidative fibers, and this fiber
type accounts for only a small portion of the rat's musculature (1).
Therefore, the nonrecirculating hindlimb perfusion technique was used
both to examine the effect of amylin across all three basic muscle
fiber types simultaneously and to eliminate any counterregulatory
effects due to changes in circulating amylin or insulin concentration
that could occur in vivo. Emphasis was placed on examining the
dose-response mechanism across fiber types by measuring second
messengers and metabolic intermediates. Amylin dosages were chosen from
those previously shown to be minimally to maximally effective in their
ability to inhibit insulin-stimulated glucose disposal in the rat (15, 19). The concentrations of insulin and glucose were selected to explore
postprandial conditions of the rat in which amylin could possibly have
an important physiological role.
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RESEARCH DESIGN AND METHODS |
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Perfusion and surgical procedure. Forty male Harlan Sprague-Dawley rats (Harlan Sprague Dawley, Indianapolis, IN), 3-4 wk of age, were purchased, housed three to a cage, and allowed access to food and water ad libitum. The temperature of the animal room was maintained at 23°C, and a 12:12-h light-dark cycle was set. All procedures used in this study were approved by the University of Texas Animal Care and Use Committee.
Rats weighing 168.4 ± 0.5 g were fasted for 4-6 h, which resulted in muscle glycogen concentration averaging 30.91 ± 0.52 µmol/g wet wt, which did not differ among fiber types. Animals were anesthetized with an intraperitoneal injection of pentobarbital sodium (6.5 mg/100 g body wt). The hindlimbs were surgically isolated, and catheters were placed in the descending aorta and vena cava, as previously described (11). Animals were killed with an intracardiac injection of pentobarbital as the hindlimbs were being washed out with 25 ml Krebs-Henseleit buffer (KHB). Catheters were then placed in line with a nonrecirculating perfusion system that provided a flow rate of 4 ml/min. Perfusate was continuously gassed (mixture 95% O2-5% CO2), and its temperature was maintained at 37°C. All perfusates consisted of KHB, pH 7.4, 4% dialyzed bovine serum albumin (ICN 105033), 30% (vol/vol) blood bank time-expired human erythrocytes, 10 mM glucose, and 200 µM pyruvate. Hindlimbs were perfused for 10 min with a perfusion medium containing 2.1 nmol/l (350 µU/ml) insulin (Lilly CP-210) and 0.0 (control), 1.0, 10.0, or 100.0 nmol/l rat amylin (H-9475; Bachem, King of Prussia, PA) or 100 nmol/l amylin plus 100 nmol/l SCT-(8Blood and tissue assays. Glucose uptake and glycogen concentration were determined in all fiber types. However, because of the small size of the soleus muscle, there was not enough sample to determine G-6-P, lactate, or cAMP concentrations for the SO fibers.
Relative changes in glucose uptake were estimated by determining the rate of incorporation of 2-deoxy-[3H]glucose tracer into muscle tissue. 2-Deoxyglucose is a nonmetabolizable glucose analog that has rates of removal from blood into muscle tissue similar to glucose under a physiological range of insulin concentration, but it is not metabolized beyond phosphorylation by hexokinase and provides a good estimate of glucose uptake in muscle tissue (21, 27). Freeze-clamped muscles from the perfusion were sectioned and weighed frozen. A 60- to 100-mg piece of each muscle or muscle section was dissolved in 1 ml 1 N KOH by incubating it for 20 min at 70°C; it was mixed and incubated an additional 10 min at 70°C. An equal volume of 1 N HCl was added to the digested samples and mixed, and aliquots of the neutralized samples were counted for 3H and 14C disintegrations per minute. 2-Deoxyglucose uptake was calculated as a percentage of the tracer concentration in the perfusate (intracellular concentration divided by extracellular concentration × 100). The amount of tracer contained within the extracellular space was determined by the amount of [14C]mannitol retained in the tissue. Muscle glycogen concentration was determined after its complete enzymatic degradation to glucose with amyloglucosidase (22). An aliquot of the KOH-digested muscle was incubated overnight in 0.3 M sodium acetate buffer, pH 4.8, that contained 5 mg/ml amyloglucosidase (Boehringer Mannheim, Mannheim, Germany). Liberated glucose was then measured using a spectrophotometric Trender reaction (no. 315, Sigma Chemical, St. Louis, MO). Perfusate supernatant samples collected during the tracing period of the perfusions were thawed and mixed well before lactate determination. For muscle tissue lactate, ~100 mg of muscle were powdered under liquid nitrogen and added to three volumes (vol/wt) of 10% perchloric acid (PCA). The sample was further homogenized in a motorized glass homogenizer and centrifuged at 2,000 g for 15 min. The perfusate and muscle supernatant samples were analyzed for lactate, as described by Hohorst (9). A portion of the muscle supernatant was neutralized with saturated (30%) KHCO3. This neutralized sample was then centrifuged at 2,000 g for 15 min and assayed for G-6-P (20). A 100-mg portion of the FO and FG quadriceps, excised ~8 min into the equilibrium period of the perfusion, was homogenized in 400 µl 6% PCA at 0°C. The sample was neutralized with saturated 30% KHCO3 before analysis. cAMP was then measured by competitive binding with labeled [3H]cAMP (kaph2, Diagnostic Product, Los Angeles, CA) (8).Statistical analysis. Individual fiber type responses were analyzed by one-way factorial or repeated-measures analysis of variance (ANOVA). Full multivariate ANOVA was run on all responses to determine overall effects, fiber type specificity, and time differences in response to the different dosages of amylin used. Significance was accepted when P values were <0.05. Individual treatment groups were compared with respective controls using Fisher's protected least significant difference post hoc test. Correlations were performed between appropriate responses.
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RESULTS |
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Insulin-stimulated 2-deoxyglucose uptake was inhibited by perfusion
with amylin in all three basic muscle fiber types, and SCT-(832) did
not attenuate this inhibition (Fig. 1). The
2-deoxyglucose uptake was negatively correlated with the dose of amylin
used, with a maximal uptake inhibition of ~40% in each fiber type.
Different fiber types had different absolute uptake responses, but
muscle fiber type did not affect the relative response to amylin or
amylin plus SCT-(8
32).
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Perfusions with amylin significantly affected glycogen metabolism. No
differences among fiber types were detected with multivariate ANOVA
analysis. Fiber types were therefore pooled for presentation in Table
1. Under control conditions and in the
presence of 1 nM amylin, there was an accumulation of muscle glycogen
during the perfusion. However, when the hindlimbs were perfused with 10 or 100 nM amylin, there was a reduction in the muscle glycogen concentration. SCT-(832) in equal molar concentrations with amylin (100 nM) was able to eliminate all the detectable amylin effect, because glycogen accumulation was essentially the same as control.
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G-6-P increased in response to amylin
in the FO and FG fibers, whereas SCT-(832) was not able to prevent
this rise in G-6-P (Fig.
2). G-6-P
concentration was correlated positively with amylin dosage and
negatively with 2-deoxyglucose uptake (Fig.
3, A and B). In the presence of amylin, FO
muscle G-6-P concentration increased with time, whereas FG muscle G-6-P did
not change beyond that which occurred during the equilibration period.
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The rise in G-6-P concentration was
accompanied by a reduction in glycogen when amylin was provided at
concentrations above 1 nM. However, when the amylin antagonist
SCT-(832) was added to the perfusate, the inverse relationship
between glycogen breakdown and G-6-P
elevation disappeared. Indeed, G-6-P
concentrations were the same in the presence of 100 nM amylin plus
SCT-(8
32) despite a complete reversal of glycogen metabolism from
degradation with amylin to synthesis when the amylin antagonist
SCT-(8
32) was added. The coperfusion of amylin and SCT-(8
32)
demonstrates that an increase in the breakdown or a decrease in
glycogen synthesis is not required for an elevation in
G-6-P.
Amylin caused an increase in muscle tissue lactate, and SCT-(832) was
able to attenuate this rise (Fig. 4). There
was a significant difference between FO and FG fiber types in lactate
response from the equilibration period to the end of perfusion. FO
muscle lactate increased with time, whereas FG muscle did not change.
The increase in muscle lactate resulted in an increase in muscle
lactate efflux, as represented by increases in venous perfusate lactate
levels. SCT-(8
32) prevented this amylin-induced efflux of lactate
(Fig. 5).
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A rise in cAMP occurred with amylin in both FO and FG fibers (Fig.
6). SCT-(832) completely blocked this
rise in cAMP. cAMP was elevated in all groups in which glycogenolysis
occurred.
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DISCUSSION |
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Although the absolute uptake of 2-deoxyglucose tracer into muscle was different among fiber types, amylin decreased insulin-stimulated uptake of tracer to the same relative extent in all three basic fiber types investigated (Fig. 1). This indicates that skeletal muscle glucose uptake is reduced by amylin, as suggested by earlier observations (7, 24, 33, 34). The different absolute rates of insulin-stimulated glucose uptake across fiber types in both normal and insulin-resistant muscle are well documented (6, 11, 28). The same relative inhibition of 40% across all fiber types demonstrates two important aspects about amylin action on glucose uptake in muscle. First, amylin is effective on all fiber types. Second, amylin efficacy appears to be roughly balanced with insulin efficacy across fiber types.
An inverse relationship between uptake of tracer and G-6-P concentration occurred with all treatments (Fig. 3). It has been hypothesized that amylin shifts the rate-limiting step of glucose uptake from transport to disposal of glucose into glycogen (24, 33). In our study, G-6-P was found to increase with increasing dosage of amylin and over time, suggesting that amylin could possibly cause an inhibition of glucose uptake by raising the intracellular G-6-P concentration and inhibiting glucose phosphorylation by hexokinase under the conditions tested (Fig. 2). The temporal increase of G-6-P also suggests that this inhibition may not have reached its peak even with 30 min of amylin exposure in the perfused hindlimb. Recently, additional support for a gradual increase in the ability of amylin to inhibit muscle glucose uptake has come from the observation that the rate of glucose disposal (Rd) gradually decreases with prolonged amylin exposure during a hyperinsulinemic euglycemic clamp (13). In addition, it has been demonstrated that amylin in plasma concentration of 300 pM can inhibit the Rd of glucose from the circulation (7). Our observations support these findings and suggest that these decreases in whole body glucose uptake are due in part to decreases in glucose uptake in all three basic muscle fiber types of the rat.
Although the reduction in muscle glucose uptake in the presence of amylin was correlated with the intracellular G-6-P concentration, we cannot exclude the possibility that amylin may have inhibited glucose transport, as this process was not evaluated in this study. Zierath et al. (34) demonstrated inhibition of 3-O-methylglucose transport with amylin; however, several research groups have been unable to demonstrate this effect on glucose transport in soleus muscle (24, 33).
The rapid decline in muscle glycogen under the two highest amylin concentrations indicates that amylin is a potent stimulus of glycogenolysis. An activation of glycogenolysis by amylin has been demonstrated by others (23, 33). Young et al. (33) reported decreases in the concentration of muscle glycogen with increasing amylin concentration in vivo. Pittner et al. (23) found that amylin reduced the glycogen concentration and increased lactate production of isolated soleus muscles in a dose-dependent manner in the absence of insulin. This reduction in muscle glycogen was associated with an increase in glycogen phosphorylase a activity.
Besides stimulating glycogenolysis, there is substantial evidence that
amylin inhibits glycogen synthesis. Deems et al. (5) reported that
amylin not only increased glycogen phosphorylase a activity but also inhibited glycogen
synthase activity. Frontoni et al. (7) found that rates of
incorporation of radioactively labeled glucose into muscle glycogen
decreased with increasing amylin dose in vivo. Also, amylin has been
found to decrease glycogen synthesis in isolated soleus muscle as
determined by the rate of
[14C]glucose
incorporation into glycogen, which involves both phosphorylation of
glucose by hexokinase and the subsequent disposal into glycogen (18,
19, 32). From these results, it would appear that amylin not only
activates glycogenolysis but also inhibits glycogen synthesis, thus
limiting or possibly eliminating a major pathway of glucose disposal.
SCT-(832) and related analogs have been shown to antagonize the
amylin inhibition of
[14C]glucose
incorporation into glycogen (2). Our results are consistent with this
observation in that glycogen content increased when SCT-(8
32) was
added to the perfusate containing amylin.
It is of interest to note that the intracellular
G-6-P levels were elevated to the same
extent after amylin exposure with or without the amylin antagonist
SCT-(832) present, despite inhibition of amylin-activated
glycogenolysis by SCT-(8
32). Because glucose uptake was reduced to
the same extent by both the amylin and amylin plus SCT-(8
32)
treatments, the G-6-P results suggest
that amylin controls intracellular
G-6-P concentration by regulating the
rate of glycolysis. This conclusion presents a paradox, for amylin alone increased rather than decreased lactate production. This discrepancy may be explained, however, by relating the rate of glycolysis to substrate concentration. That is, all treatment groups
containing amylin exhibited an inhibition of glycolysis, as defined by
a slower rate of glycolysis for a given
G-6-P concentration compared with
control. Therefore, amylin may cause a relative inhibition of
glycolysis while mobilizing substrate from glycogen. A likely control
point for regulation of glycolysis by amylin would be
phosphofructokinase, as this enzyme is allosterically regulated by many
metabolites.
As previously mentioned, the breakdown in glycogen was associated with
an increase in muscle lactate concentration and muscle lactate efflux,
which continued to increase with time (Figs. 4 and 5). Young et al.
(30) showed that it takes 30 min for blood lactate to peak after a
bolus amylin injection. These observations further support our
contention that the action of amylin may gradually increase with time.
The SCT-(832) analog AC-187 has been shown to attenuate lactate
efflux from muscle (29), and we have demonstrated that SCT-(8
32) is
also effective in eliminating this amylin-induced lactate efflux (Figs.
4 and 5). However, the decreased rate of amylin-induced lactate
production with SCT-(8
32) present and G-6-P elevated further supports our
contention that the relative rate of glycolysis is slowed by amylin
(Figs. 1 and 2).
The increases in glycogenolysis and lactate production in response to
amylin were similar to effects that occur with agents that act via
cAMP-mediated pathways. In the present study, we found that amylin
significantly elevated the cAMP concentration of FO and FG muscle. An
intracellular rise in cAMP can cause a prolonged activation of glycogen
phosphorylase and inhibition of glycogen synthase through the
activation of protein kinase A, but evidence against cAMP as a second
messenger for amylin action has been reported (5, 16). In both myocytes
and isolated soleus muscles, no increase in intracellular cAMP was
found after 15 min of incubation with dosages of amylin that
effectively inhibited glucose uptake (16). Furthermore, Deems et al.
(5) did not see a rise in cAMP in isolated soleus muscle after 5 min of
incubation with 100 nM amylin, but they demonstrated consistent changes
in glycogen phosphorylase a and
glycogen synthase activities. However, Pittner et al. (23) recently
reported that 100 nM rat amylin increased the cAMP concentration
threefold in isolated soleus muscle strips. The rise in cAMP peaked
within 5 min and returned to basal levels between 20 and 40 min of
incubation. In response to the rise in cAMP there was a prolonged
increase in glycogen phosphorylase a
activity, a decrease in glycogen concentration, and an enhanced lactate
production. Our results are, therefore, in agreement with those of
Pittner et al. (23) and suggest that the effects of amylin are mediated
in part through a signaling mechanism similar to that of -adrenergic
agonists. However, we also demonstrated that glucose uptake can be
inhibited by amylin without this system being activated (Figs. 1 and
6), and this could possibly explain why Kreutter et al. (16) observed
inhibition of glucose uptake without a preceding rise in cAMP.
Amylin may mediate its glycogen effects through a calcitonin
gene-related peptide (CGRP) receptor, and SCT-(832) may be a CGRP
receptor antagonist (12, 25). CGRP is a 37-amino acid peptide that
differs only slightly from amylin (4, 25). One of the two types of CGRP
receptors is known to be coupled to adenylyl cyclase, and amylin can
also activate this receptor (25). Evidence exists suggesting that there
may be amylin-specific receptors in addition to these CGRP receptors
(2, 12, 25). However, until now no evidence existed for multiple
postreceptor effects that could be separated by an antagonist. The
existence of multiple receptors for amylin and CGRP is based on binding
data or sensitivity to antagonism of the same biological effect (2, 12,
25). The demonstration of possibly two distinct pathways of amylin action could help unravel the disparate findings of other researchers (5, 16, 17, 23). However, studies on both binding and functional
responses will be needed before it can be determined whether the two
functional effects demonstrated are the result of distinct receptors or
some anomalous single receptor.
For several metabolic responses, a large dose of amylin was needed
before a significant effect could be detected. The magnitude of each
response also varied. The largest concentration of amylin used in this
study was approximately one order of magnitude greater than
concentrations reported in the rat (15) and two orders of magnitude
greater than concentrations reported for humans (3). The large
discrepancy between effective dosage in vitro and reported in vivo
values has cast doubt on any physiological role for amylin. However,
several in vivo studies have suggested that amylin is effective at
physiological concentrations. Vine et al. (29) demonstrated that an
antagonist based on SCT-(832) was able to decrease lactate efflux
across the rat hindlimb. Frontoni et al. (7) demonstrated that plasma
concentrations of 300 pM could change the fraction of plasma glucose
that was partitioned to glycogen and glycolysis in muscle. Also, Young
et al. (33) demonstrated that antibody measurements underestimate in
vitro amylin concentration. This observation would suggest that the in
vivo measurement of amylin concentration may not be reliable.
Regardless of the physiological role of amylin, understanding its
mechanism of action is very important, because amylin agonists and
antagonists are being developed for use in humans (14, 29).
In conclusion, this is the first study to demonstrate at least two
functionally different mechanisms of action for amylin on glucose
metabolism. One mechanism is cAMP mediated and acts on glycogen, and
the second inhibits or regulates glycolysis, elevates
G-6-P, and inhibits glucose uptake
independently of cAMP mediation. This could explain why several
researchers have not observed cAMP as a mediator of amylin action and
could therefore explain some of the discrepancies in the literature (5,
16). We conclude that SCT-(832) is an effective antagonist of
amylin-activated glycogenolysis and lactate efflux, a view which
supports the use of compounds based on this peptide as inhibitors of
the Cori cycle for controlling blood glucose in NIDDM (29, 31).
However, such compounds may not be effective in attenuating amylin
inhibition of insulin-stimulated glucose uptake and would therefore not
be expected to reduce peripheral insulin resistance. Thus it appears that amylin may work through several pathways to control glucose metabolism in muscle and that these pathways can be separated with the
antagonist SCT-(8
32).
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ACKNOWLEDGEMENTS |
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We thank Suzie Vasquez for technical assistance.
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FOOTNOTES |
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This study was supported by a grant from Pfizer Inc.
Address for reprint requests: J. L. Ivy, Bellmont Hall, Rm. 222, Dept. of Kinesiology and Health Education, Univ. of Texas at Austin, Austin, TX 78712.
Received 31 March 1997; accepted in final form 17 September 1997.
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REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Ariano, M. A.,
R. B. Armstrong,
and
V. R. Edgerton.
Hindlimb muscle fiber populations of five mammals.
J. Histochem. Cytochem.
21:
51-55,
1973[Medline].
2.
Beaumont, K.,
R. A. Pittner,
C. X. Moore,
D. Wolfe-Lopez,
K. S. Prickett,
A. A. Young,
and
T. J. Rink.
Regulation of muscle glycogen metabolism by CGRP and amylin: CGRP receptors not involved.
Br. J. Pharmacol.
115:
713-715,
1995[Abstract].
3.
Butler, P. C.,
J. Chou,
W. B. Carter,
Y. N. Wang,
B. H. Bu,
D. Chang,
J. K. Chang,
and
R. A. Rizza.
Effects of meal ingestion on plasma amylin concentration in NIDDM and nondiabetic humans.
Diabetes
39:
752-756,
1990[Abstract].
4.
Cooper, G. J.,
A. C. Wilis,
A. Clark,
R. C. Turner,
R. B. Slim,
and
K. B. Reid.
Purification and characterization of a peptide from amylin-rich pancreases of type 2 diabetic patients.
Proc. Natl. Acad. Sci. USA
84:
8628-8632,
1987[Abstract].
5.
Deems, R. O.,
R. W. Deacon,
and
D. A. Young.
Amylin activates glycogen phosphorylase and inactivates glycogen synthase via a cAMP-independent mechanism.
Biochem. Biophys. Res. Com.
174:
716-720,
1991[Medline].
6.
Etgen, G. J., Jr.,
J. T. Brozinick, Jr.,
H. Y. Kang,
and
J. L. Ivy.
Effects of exercise training on skeletal muscle glucose uptake and transport.
Am. J. Physiol.
264 (Cell Physiol. 33):
C727-C733,
1993
7.
Frontoni, S.,
S. B. Choi,
D. Banduch,
and
L. Rossetti.
In vivo insulin resistance induced by amylin primarily through inhibition of insulin-stimulated glycogen synthesis in skeletal muscle.
Diabetes
40:
568-573,
1991[Abstract].
8.
Gilman, A. G.
A protein binding assay for adenosine 3': 5' cyclic monophosphate.
Proc. Natl. Acad. Sci. USA
67:
305-312,
1970[Abstract].
9.
Hohorst, H. J.
Determination of L-lactate with LDH and DPH.
In: Methods of Enzymatic Analysis. New York: Academic, 1965, p. 265-270.
10.
Inoue, K.,
A. Hisatomi,
F. Umeda,
and
H. Nawata.
Amylin release from perfused rat pancreas in response to glucose and arginine.
Diabetes Res. Clin. Pract.
10:
189-192,
1990[Medline].
11.
Ivy, J. L.,
W. M. Sherman,
C. L. Cutler,
and
A. L. Katz.
Exercise and diet reduce muscle insulin resistance in obese Zucker rat.
Am. J. Physiol.
251 (Endocrinol. Metab. 14):
E299-E305,
1986
12.
Kenney, M. A.,
C. X. Moore,
R. Pittner,
and
K. Beaumont.
Salmon calcitonin binding and stimulation of cyclic AMP generation in rat skeletal muscle.
Biochem. Biophys. Res. Commun.
197:
8-14,
1993[Medline].
13.
Kim, J. K.,
and
J. H. Youn.
Prolonged suppression of glucose metabolism causes insulin resistance in rat skeletal muscle.
Am. J. Physiol.
272 (Endocrinol. Metab. 35):
E288-E296,
1997
14.
Kolterman, O. G.,
A. Gottlieb,
C. Moyses,
and
W. Colburn.
Reduction of postprandial hyperglycemia in subjects with IDDM by intravenous infusion of AC137, a human amylin analogue.
Diabetes Care
18:
1179-1182,
1995[Abstract].
15.
Kreutter, D.,
S. J. Orena,
A. J. Torchia,
W. Soeller,
and
R. W. Stevenson.
Amylin mRNA and plasma peptide levels in animal models of NIDDM (Abstract).
Diabetes
40:
159A,
1991.
16.
Kreutter, D. K.,
S. J. Orena,
A. J. Torchia,
L. G. Contillo,
G. C. Andrews,
and
R. W. Stevenson.
Amylin and CGRP induce insulin resistance via a receptor distinct from cAMP-coupled CGRP receptor.
Am. J. Physiol.
264 (Endocrinol. Metab. 27):
E606-E613,
1993
17.
Lawrence, J. C., Jr.,
and
J. N. Zhang.
Control of glycogen synthase and phosphorylase by amylin in rat skeletal muscle. Hormonal effects on the phosphorylation of phosphorylase and on the distribution of phosphate in the synthase subunit.
J. Biol. Chem.
269:
11595-11600,
1994
18.
Leighton, B.,
and
G. J. Cooper.
Pancreatic amylin and calcitonin gene-related peptide cause resistance to insulin in skeletal muscle in vitro.
Nature
335:
632-635,
1988[Medline].
19.
Leighton, B.,
and
E. Foot.
The effects of amylin on carbohydrate metabolism in skeletal muscle in vitro and in vivo.
Biochem. J.
269:
19-23,
1990[Medline].
20.
Lowry, O. H.,
and
J. V. Passonneau.
A Flexible System of Enzymatic Analysis. New York: Academic, 1972.
21.
Mészáros, K.,
C. H. Lang,
D. M. Hargrove,
and
J. J. Spitzer.
Tissue glucose utilization during epinephrine-induced hyperglycemia.
J. Appl. Physiol.
67:
1770-1775,
1989
22.
Passonneau, J. V.,
and
V. R. Lauderdale.
A comparison of three methods of glycogen measurement in tissue.
Anal. Biochem.
60:
404-412,
1974.
23.
Pittner, R.,
K. Beaumont,
A. Young,
and
T. Rink.
Dose-dependent elevation of cyclic AMP, activation of glycogen phosphorylase, and release of lactate by amylin in rat skeletal muscle.
Biochem. Biophys. Acta
1267:
75-82,
1995[Medline].
24.
Pittner, R. A.,
D. Wolfe-Lopez,
A. A. Young,
and
T. J. Rink.
Amylin and epinephrine have no direct effect on glucose transport in isolated rat soleus muscle.
FEBS Lett.
365:
98-100,
1995[Medline].
25.
Poyner, D.
Pharmacology of receptors for calcitonin gene-related peptide and amylin.
Trends Pharmacol. Sci.
16:
424-428,
1995[Medline].
26.
Rink, T. J.,
K. Beaumont,
J. Koda,
and
A. Young.
Structure and biology of amylin.
Trends Pharmacol. Sci.
14:
113-118,
1993[Medline].
27.
Rubart, M.,
W. Breull,
and
N. Hahn.
Regional metabolic rate of exogenous glucose in the isoprenaline and dobutamine stimulated canine myocardium as estimated by the 2-deoxy-D[1-14C]glucose method.
Int. J. Rad. Appl. Instrum. B.
18:
157-166,
1991[Medline].
28.
Sherman, W. M.,
A. L. Katz,
C. L. Cutler,
R. T. Withers,
and
J. L. Ivy.
Glucose transport: locus of muscle insulin resistance in obese Zucker rats.
Am. J. Physiol.
255 (Endocrinol. Metab. 18):
E374-E382,
1988
29.
Vine, W.,
P. Smith,
R. LaChappell,
T. J. Rink,
and
A. A. Young.
Lactate production from the rat hindlimb is increased after glucose administration and is suppressed by a selective amylin antagonist: evidence for action of endogenous amylin in skeletal muscle.
Biochem. Biophys. Res. Comun.
216:
554-559,
1995[Medline].
30.
Young, A. A.,
G. J. S. Cooper,
P. Carlo,
T. J. Rink,
and
M. W. Wang.
Response to intravenous injections of amylin and glucagon in fasted, fed, and hypoglycemic rats.
Am. J. Physiol.
264 (Endocrinol. Metab. 27):
E943-E950,
1993
31.
Young, A. A.,
B. Gedulin,
L. S. Gaeta,
K. S. Prickett,
K. Beaumont,
E. Larson,
and
T. J. Rink.
Selective amylin antagonist suppresses rise in plasma lactate after intravenous glucose in the rat. Evidence for a metabolic role of endogenous amylin.
FEBS Lett.
343:
237-241,
1994[Medline].
32.
Young, A. A.,
B. Gedulin,
D. Wolfe-Lopez,
H. E. Greene,
T. J. Rink,
and
G. J. S. Cooper.
Amylin and insulin in rat soleus muscle: dose responses for cosecreted noncompetitive antagonists.
Am. J. Physiol.
263 (Endocrinol. Metab. 26):
E274-E281,
1992
33.
Young, D. A.,
R. O. Deems,
R. W. Deacon,
R. H. McIntosh,
and
J. E. Foley.
Effects of amylin on glucose metabolism and glycogenolysis in vivo and in vitro.
Am. J. Physiol.
259 (Endocrinol. Metab. 22):
E457-E461,
1990
34.
Zierath, J. R.,
D. Galuska,
A. Engstrom,
K. H. Johnson,
C. Betsholtz,
P. Westermark,
and
H. Wallberg-Henriksson.
Human islet amyloid polypeptide at pharmacological levels inhibits insulin and phorbol ester-stimulated glucose transport in vitro incubated human muscle strips.
Diabetologia
35:
26-31,
1992[Medline].