Vol. 279, Issue 5, G903-G909, November 2000
Metabolism and acid secretory effect of sulfated and nonsulfated
gastrin-6 in humans
C. Palnæs
Hansen,
F.
Stadil, and
J. F.
Rehfeld
Departments of Gastrointestinal Surgery C and Clinical
Biochemistry, Rigshospitalet, University of Copenhagen, DK-2100
Copenhagen, Denmark
 |
ABSTRACT |
The antral hormone gastrin is
synthesized by processing progastrin into different peptides that
stimulate gastric secretion. The effect on acid secretion depends
mainly on the metabolic clearance rate of the peptides, but some of
them may differ in potency and maximum acid output at similar
concentrations in plasma. Sulfated and nonsulfated gastrin-6 are the
smallest circulating bioactive gastrins in humans. Their effect and
metabolism have now been investigated in nine normal subjects and
compared with nonsulfated gastrin-17, a main product of progastrin.
Maximum acid output after stimulation with gastrin-17, sulfated
gastrin-6, and nonsulfated gastrin-6 were 28.3 ± 2.0, 24.5 ± 2.0 (P < 0.02), and 19.3 ± 2.3 (P < 0.05) mmol H+/50 min, respectively,
and the corresponding EC50 values were 43 ± 6, 24 ± 2 (P < 0.01), and 25 ± 2 (not
significant) pmol/l. The half-life of gastrin-17 was 5.3 ± 0.3 min, the metabolic clearance rate (MCR) was 16.5 ± 1.3 ml · kg
1 · min1, and the
apparent volume of distribution (Vd) was 124.3 ± 9.6 ml/kg. The half-lives of sulfated and nonsulfated gastrin-6 were 2.1 ± 0.3 and 1.9 ± 0.3 min, the MCRs were 42.8 ± 3.7 and 139.4 ± 9.6 ml kg1 min1
(P < 0.01), and the Vd were 139.0 ± 30.5 and 392.0 ± 81.6 (P < 0.01) ml
kg1. All pharmacokinetic parameters differed
significantly from gastrin-17 (P < 0.01). We conclude
that gastrin 6 has a higher potency but a lower efficacy than
gastrin-17. The efficacy of gastrin-6 is increased by tyrosine
O-sulfation, which also enhances the protection against elimination.
gastric acid; pharmacodynamics; pharmacokinetics
| |
INTRODUCTION |
GASTRIN WAS
THE FIRST GASTROINTESTINAL hormone to have its structure
determined (9). Gastrin is a major regulator of gastric acid secretion and growth of gastric mucosa cells (for review, see Ref.
30). The active site of gastrin is the COOH-terminal tetrapeptide amide
Trp-Met-Asp-Phe-NH2 (17). Progastrin
is synthesized in antral G cells and processed into a number of
bioactive peptides, of which the heptadecapeptide gastrin-17 is
the main product (9, 11, 23) (Fig.
1). All bioactive gastrin peptides are
carboxyamidated and exist in nonsulfated and sulfated forms, due to
O-sulfation of the tyrosyl residue (Tyr6), as
counted from the COOH terminus (1, 9, 11). A minor fraction of gastrin-17 is cleaved in G cells and released as short COOH-terminal peptides (24). These peptides have been
identified in porcine and human antral tissue as a mixture of
gastrin-7, -6, and -5, of which sulfated gastrin-6 is the predominant
form released to antral venous blood (10, 22).
View larger version (28K):
[in this window]
[in a new window]
|
Fig. 1.
Simplified processing scheme for human progastrin in antral G
cells. The  -amino group of Gly72 in glycine-extended
gastrins constitutes the amide donor for bioactive end products. All
bioactive gastrins are carboxyamidated with the COOH-terminal sequence
Trp-Met-Asp-Phe-NH2, corresponding to sequence 68-71
of progastrin. Biosynthetic end products exist in sulfated and
nonsulfated forms.
|
|
The kinetics and pharmacodynamics of gastrin-52, -34, -17, and -14 have
been well described (6, 8, 18, 31). Gastrin-17 is
equipotent with gastrin-34 at similar plasma concentrations, and
sulfation influences neither gastric acid secretion nor metabolic clearance rate (MCR) (4, 5, 8). In cats, however, short gastrin peptides have a lower potency than gastrin-17, and sulfation reduces their MCR (3, 12).
So far, human studies of gastrin-6 have not been reported. Therefore,
we have now investigated the pharmacodynamics and pharmacokinetics of
sulfated and nonsulfated gastrin-6 in humans. The peptides were
compared with nonsulfated gastrin-17, which has been used in most
studies of gastrin physiology.
| |
MATERIALS AND METHODS |
Peptides
Sulfated and nonsulfated human gastrin-6 were custom synthesized
by Cambridge Research Biochemicals (Zeneca; Alderley Park, UK). The
content and purity of the peptides were controlled by amino acid
analysis (LKB amino acid analyzer 4000 with fluorescence detection; LKB
Biochrom, Cambridge, UK) and reverse-phase HPLC (Hewlett-Packard 1084 B; Hewlett-Packard, Palo Alto, CA). Synthetic human nonsulfated
gastrin-17 was purchased from Sigma Chemical (St. Louis, MO).
Subjects
The studies were carried out in nine healthy volunteers (6 men
and 3 women, ages 22-36 yr; Table 1)
without a history of medical or surgical illness. Peak acid output was
determined in all subjects before the studies by intramuscular
injection of 6 µg pentagastrin (Peptavlon; Zeneca). Informed consent
was obtained, and the study was approved by the Ethics Committee for
Medical Research in Copenhagen in accordance with the Helsinki II
declaration.
View this table:
[in this window]
[in a new window]
|
Table 1.
Age, body surface, and peak acid output after intramuscular injection
of 6 µg pentagastrin in 9 subjects
|
|
Experimental Procedures
Gastric acid secretion during infusion of nonsulfated gastrin-17,
sulfated gastrin-6, and nonsulfated gastrin-6.
Three experiments were carried out randomly in each subject on separate
days. After an overnight fast, a nasogastric tube was inserted with the
tip in the antrum under fluoroscopic control. After residual gastric
content was evacuated, gastric juice was aspirated continuously by
intermittent pump suction (Egnell) in periods of 10 min with the
subject in the supine position. The recovery of gastric juice was
determined by continuous infusion of a marker in the lateral lumen of
the tube (230 kBq 57Co-labeled cobalamin, 1.25 mg
cobalamin, and 1 g human albumin diluted in 1,000 ml isotonic
saline; 60 ml/h). The lateral lumen ended 10 cm proximal to the
openings of the central canal. The volume of gastric juice was measured
for each 10-min period, and the concentration of H+ was
determined by titration to pH 7.0 with an autotitrator (PHM 26;
Radiometer, Copenhagen, Denmark). Sterile filtrated gastrin peptides
were diluted in isotonic saline containing 1 g/l of human albumin. The
syringes were weighed before and after the infusions, and remaining
peptide was stored at 
20°C until radioimmunoassay.
Each infusion experiment began with a 50-min control period during
which isotonic saline was infused intravenously at 30 ml/h with a pump
(Perfusor VII; Braun, Melsungen, Germany). After the control period,
one of three peptides was infused in four consecutive doses
(nonsulfated gastrin-17 and sulfated gastrin-6: 40, 80, 120, and 160 pmol · kg1 · h1;
nonsulfated gastrin-6: 120, 240, 360, and 480 pmol · kg1 · h1). The dose
rate at which maximum acid output was achieved was determined in pilot
studies. Each dose interval lasted 50 min, and venous blood samples
were taken from the opposite arm every 10 min from the start of the infusion.
Metabolism of nonsulfated gastrin-17, sulfated gastrin-6, and
nonsulfated gastrin-6.
After termination of the infusion, the intravenous catheter was rapidly
removed and blood samples were taken at 1, 2, 3, 4, 5, 10, 15, 20, 30, 45, and 60 min to determine the half-life of the peptides in plasma.
In vitro degradation of nonsulfated gastrin-17, sulfated
gastrin-6, and nonsulfated gastrin-6.
Venous blood from normal subjects who had fasted overnight was
collected in dry heparinized tubes. Known amounts of the peptides were
added to plasma and incubated at 37°C for 0, 1, 2, 4, 8, and 24 h. Then the incubation samples were immediately frozen in liquid
nitrogen and stored at 20°C until radioimmunoassay.
Laboratory Analyses
Radioimmunoassay.
Blood was collected in chilled tubes containing 50 IU of heparin and
250 µl of aprotinin (5,000 kallikrein inhibitor units) and
immediately placed on ice. After centrifugation, plasma was stored at
20°C until radioimmunoassay. All radioimmunoassay measurements were performed by previously described assays developed in our laboratory. The concentration of gastrin-17 was measured using antiserum 2604 (25, 28). This antiserum was raised against the 2-17 sequence of human nonsulfated gastrin-17 and is specific for the bioactive COOH-terminal heptapeptide. It binds both
sulfated and nonsulfated gastrin-71, -52, -34, and -17 with equimolar
potency, whereas the reactivity with the homologous hormone
cholecystokinin is <0.5% (25). Synthetic human
gastrin-17 was used as standard, and monoiodinated
125I-gastrin-17 was used as tracer (27).
Sulfated and nonsulfated gastrin-6 were measured using antiserum 2609 after extraction of the peptides from plasma. Antiserum 2609 was also
raised against the 2-17 fragment of human nonsulfated gastrin-17
(20, 25). But contrary to antiserum 2604, which requires
an epitope of seven residues or more for binding, antiserum 2609 requires only the COOH-terminal tetrapeptide amide sequence, although
increasing chain length increases antibody binding. The reactivity with
gastrin-34 is 63% and with cholecystokinin-8 is 20%. The
cross-reactivity with cholecystokinin was without significance in
this study, since the concentration of cholecystokinin in plasma from
fasting normal subjects is 1 pmol/l or less (21). For
measurement of sulfated and nonsulfated gastrin-6 in plasma, 1 ml of
sample was extracted with 2 ml of 96% ethanol and the supernatant was evaporated under airflow. The dried extracts were reconstituted to
original volume with assay buffer. Sulfated and nonsulfated gastrin-6
were used as standards, and monoiodinated 125I-labeled
gastrin-17 was used as tracer.
All samples of each experiment were measured in a single assay. The
recovery of the peptides at different plasma concentrations are shown
in Table 2.
Chromatography.
Blood samples drawn at the termination of the last dose interval during
infusion of nonsulfated gastrin-17, sulfated gastrin-6, and nonsulfated
gastrin-6 were studied by gel chromatography. Plasma from all subjects
was pooled, and 1-ml samples were applied to Sephadex G-50 superfine
columns (10 × 1,000 mm; Pharmacia, Uppsala, Sweden) and eluted
with 0.125 mol/l NH4HCO3, pH 8.2, at room
temperature with a flow rate of 3 ml/h. Void volume and total volume
were determined by elution of 125I-labeled albumin and
22NaCl, and fractions of 1 ml were collected and assayed
with antisera 2604 and 2609. The elution positions,
Kd, were calculated as
where Ve is the elution volume of the peptides, and
Vo and Vt are the elution volumes of
125I-labeled albumin and 22NaCl, respectively.
Calculations and Statistical Analysis
Correction for nonrecovered gastric juice was made for every
sampling period as
where Vc is the corrected volume (in ml),
Va is the aspirated volume, Qi is the amount of
radioactivity infused (in counts/min), and Qa is the amount
of aspirated radioactivity. Maximum acid output was defined as the
maximum acid secretion during one dose interval (mmol H+/50
min). Peak acid output, expressed as mmol H+/h, was defined
as the two highest consecutive samples multiplied by 2 (pentagastrin
test) or 3 to yield a 1-h value (2).
The pharmacodynamics of the peptides were evaluated by three
parameters: EC50, efficacy (maximum response), and potency.
EC50 was estimated from a Hill plot (14),
which is the logit of the secretory response vs. log plasma
concentration. The theoretical maximum acid output (Em) was
estimated by linear transformation of the Michaelis-Menten kinetics
according to Hofstee (7). This transformation has the
equation
where Ex is the response and Cx the
plasma concentration of the peptide. The slope of the line
(km) corresponds to EC50 and the
intercept of the ordinate corresponds to Em.
Potency was defined as effect at a given plasma concentration evaluated
from the course of the log concentration-response (LCR) curve. The
curve was computed from the equation
where Emax is the maximum response and the
coefficient s is the slope of the Hill plot.
The pharmacokinetic analysis was made according to a one-compartment,
open model
where the subscripts refer to plasma concentrations (C)
at zero time and t. Postinfusional plasma concentrations
were plotted on semilogarithmic graph paper after subtraction of basal
values. Linear regression of the logarithm of concentrations vs. time was computed to yield the slope (ke) from which
the half-life was determined by division with 0.693. The MCR was
calculated by dividing dose rate with the plateau increment in plasma
gastrin, and the apparent volume of distribution (Vd) was
calculated by dividing clearance with ke. The
plateau concentration of gastrin was taken as the mean of the two
values obtained during the final 20-min infusion of the last dose.
Results are expressed as means ± SE. Curve fitting was made from
linear and nonlinear regression using GraphPad Prism (GraphPad Software, San Diego, CA). Data were analyzed using Wilcoxon's test for
paired samples and Friedman's test for analysis of variance. P values <0.05 were considered significant.
| |
RESULTS |
Effective Dose Rates and Gastrin Concentration in Plasma
The effective dose rates were calculated from the concentration of
peptide in the infusion lines as shown in Fig.
2. During infusion, a concentration
plateau was reached for all peptides within each of the four dose
intervals.
View larger version (22K):
[in this window]
[in a new window]
|
Fig. 2.
Plasma concentrations ( ) and
gastric acid output per 10 min ( ) (means ± SE)
during infusion of nonsulfated gastrin-17 (A), sulfated
gastrin-6 (B), and nonsulfated gastrin-6 (C) in
normal subjects.
|
|
Acid Output
The acid output before infusion of nonsulfated gastrin-17 was
5.2 ± 0.7 mmol H+/50 min and increased stepwise to
15.7 ± 2.2 (P < 0.01), 26.2 ± 3.1 (P < 0.001), 25.6 ± 2.8, and 26.4 ± 2.4 [not significant (NS)] mmol H+/50 min during the four
consecutive dose intervals (Fig. 2). During infusion of sulfated
gastrin-6, acid output increased from 5.7 ± 0.7 to 12.5 ± 1.2 (P < 0.05), 20.1 ± 2.5 (P < 0.005), 22.3 ± 2.2, and 23.6 ± 1.7 (NS) mmol
H+/50 min, and the output of nonsulfated gastrin-6
increased from 4.5 ± 0.9 to 10.6 ± 1.6 (P < 0.005), 17.3 ± 1.7 (P < 0.001), 19.6 ± 2.0 (P < 0.001), and 18.9 ± 1.9 (NS) mmol
H+/50 min. Maximum and peak acid output of nonsulfated
gastrin-17, sulfated gastrin-6, and nonsulfated gastrin-6 differed
significantly, as shown in Table 3. The
theoretical Em of nonsulfated gastrin-17 and sulfated
gastrin-6 were similar, both being significantly above the
Em of nonsulfated gastrin-6 (Table 3). The EC50
of nonsulfated gastrin-17 exceeded the EC50 of sulfated and
nonsulfated gastrin-6 (P < 0.01); the respective
concentrations in plasma estimated from the regression lines were
43 ± 6 (r = 0.91), 24 ± 2 (r = 0.92), and 25 ± 2 (r = 0.90)
pmol/l (Fig. 3). LCR curves computed from
EC50 and the respective Hill coefficients are shown in Fig.
4.
View larger version (15K):
[in this window]
[in a new window]
|
Fig. 3.
Hill plot. Logit to gastric acid output E (mmol
H+/10 min) vs. concentration of nonsulfated gastrin-17,
sulfated gastrin-6, and nonsulfated gastrin-6 in plasma. The Hill
coefficient (s) is the slope of the curve, and r
is the coefficient of correlation. Nonsulfated gastrin-17:
s = 4.9, r = 0.91; sulfated gastrin-6:
s = 4.9, r = 0.92; nonsulfated
gastrin-6: s = 7.4, r = 0.90.
|
|
View larger version (18K):
[in this window]
[in a new window]
|
Fig. 4.
Log concentration-response curves of nonsulfated
gastrin-17, sulfated gastrin-6, and nonsulfated gastrin-6.
|
|
Metabolism
The elimination of COOH-terminal immunoreactivity in plasma after
infusion of the three peptides was monoexponential (Fig. 5). The half-life, MCR, and
Vd of nonsulfated gastrin-17 were 5.3 ± 0.3 min,
16.5 ± 1.3 ml · kg1 · min1, and
124.3 ± 9.6 ml/kg, respectively. For sulfated and nonsulfated gastrin-6, half-lives were 2.1 ± 0.3 and 1.9 ± 0.3 min
(NS), MCRs were 42.8 ± 3.7 and 139.4 ± 9.6 ml · kg1 · min1
(P < 0.01), and Vd were 139.0 ± 30.5 and 392.0 ± 81.6 ml/kg (P < 0.01). All
parameters of the hexapeptides differed significantly from those of
nonsulfated gastrin-17 (P < 0.01).
View larger version (10K):
[in this window]
[in a new window]
|
Fig. 5.
The elimination of nonsulfated gastrin-17 (A),
sulfated gastrin-6 (B), and nonsulfated gastrin-6
(C) in normal subjects.
|
|
Chromatography
Gel chromatography of plasma sampled during infusion of sulfated
and nonsulfated gastrin-6 revealed peaks that eluted at the positions
of the standard calibration peptides (Fig.
6).
View larger version (11K):
[in this window]
[in a new window]
|
Fig. 6.
Gel chromatography of pooled plasma sampled from normal subjects
during infusion of sulfated (A) and nonsulfated
(B) gastrin-6. Samples (1 ml) were applied to Sephadex G-50
superfine columns (10 × 1,000 mm). Eluates were assayed using
antiserum 2609.
|
|
In Vitro Degradation of Peptides
There was a time-dependent loss of nonsulfated gastrin-17 as well
as of sulfated and nonsulfated gastrin-6 after incubation in plasma.
The concentrations of nonsulfated gastrin-17 declined to 85, 73, 56, 30, and 18% after 1, 2, 4, 8, and 24 h of incubation, respectively. The concentrations of sulfated gastrin-6 declined to 47, 28, 20, 12, and 4%, and the concentrations of nonsulfated gastrin-6
declined to 55, 15, 4, 2, and 1% at the same intervals (Fig.
7).
View larger version (17K):
[in this window]
[in a new window]
|
Fig. 7.
Loss of immunoreactivity after incubation of nonsulfated
gastrin-17, sulfated gastrin-6, and nonsulfated gastrin-6 in plasma at
37°C up to 24 h.
|
|
| |
DISCUSSION |
This study showed that gastrin-6 has a higher potency but a lower
efficacy than nonsulfated gastrin-17. The efficacy of gastrin-6, however, increased by tyrosine sulfation, which also decreased the MCR.
When the theoretical Em was calculated from
Michaelis-Menten kinetics of the concentration-response data, the
efficacy of sulfated gastrin-6 and nonsulfated gastrin-17 was not
significantly different but exceeded the Em of nonsulfated
gastrin-6. Comparison between potencies were more complex because of
the different slope of the LCR curve. Thus different values would
emerge depending on the intensity of effect at which comparisons were
made. However, the EC50 of the hexapeptides was lower than
the EC50 of nonsulfated gastrin-17.
Due to the different rates of metabolism, dose rates of the peptides
had to be different. Although plasma concentrations of the hexapeptides
did not reach the same level as nonsulfated gastrin-17, no further
increase in acid output was recorded after the third dose interval of
either sulfated nor nonsulfated gastrin-6. Fading, i.e., decreased
response with time, may distort dose-response studies when increasing
doses are administrated consecutively without intervening rest periods.
Our secretory data did not suggest fading, and peak acid output during
infusion of nonsulfated gastrin-17 reached the same level as observed
during the preceding pentagastrin test. Calculation of the theoretical
value Em remains controversial. The method requires that
concentration and response follow Michaelis-Menten kinetics, a
precondition that was met in our study. But the reliability of the
calculations also depends on the mathematical transformation of the
Michaelis-Menten equation and the error of the data. However, it has
been shown experimentally that the Hofstee transformation is acceptable
even when response is subject to a considerable error (7).
Studies of small gastrin peptides have so far been restrained due to a
lack of useful radioimmunoassays. Dose-response studies of tetra- and
pentagastrin as well as the commercial analog of pentagastrin
(Peptavlon) have previously been undertaken to examine their use in
gastric function tests (21). Experiments in cats showed
that the potencies of tetra- and pentagastrin were lower than the
potency of nonsulfated gastrin-17. But since the results were evaluated
from the respective dose rates of the peptides, the difference could be
explained by the higher MCR of the small peptides (3). In
another study, the efficacy of the modified hexapeptide amide fragment
of gastrin-17, butyl-oxycarbonyl gastrin-6 (BOC-gastrin-6),
was equal to that of nonsulfated gastrin-17, but potency was lower when
circulating concentrations were taken into account (12).
This observation was explained by a higher binding affinity of
nonsulfated gastrin-17 to its receptor (30). Extrapolation
of results between species needs caution, especially for peptide
analogs. However, other studies suggest that not only the structure but
also the size of the peptide may influence the secretory response.
Hence, gastrin-17 has a similar efficacy and potency to gastrin-34 and
-14 in humans and animals (6, 8), whereas gastrin-52
studied under conditions similar to the present study revealed a lower
efficacy than nonsulfated gastrin-17 (18). Gastrin-52 is
the largest progastrin product examined so far, and since the half-life
is ~50 min, the concentration-response was not studied during steady
state concentration in plasma. Therefore, it is possible that
differences in equilibration time between plasma and receptor may have
influenced the results. In the present study, steady state was achieved
for all three peptides during each dose interval. With reference to
earlier results, it looks as if medium-sized gastrins like gastrin-34,
-17, and -14 may have a higher efficacy than peptides with either a
shorter or a longer chain length.
Sulfation of gastrin peptides is another modification that we found had
an effect on gastric acid output. Tyrosine O-sulfation is a
common posttranslational modification of peptides and proteins, and for
some peptides it is necessary for biological activity (5, 15,
26). Gastrin retains its biological activity after desulfation,
and studies in both animals and humans have shown that the efficacy and
EC50 of sulfated and nonsulfated gastrin-17 are similar
(4, 13). However, the higher efficacy of sulfated gastrin-6 compared with its nonsulfated counterpart, as found in the
present study, suggests that the biological activity of short gastrin
peptides is enhanced by sulfation of tyrosine.
Gastrin-6 had a higher MCR than gastrin-17, which is in keeping with
the general experience of an inverse relationship between MCR and
peptide length. Whether or not sulfation of gastrin also changes, the
MCR has been a subject of discussion. In one study, sulfation of
gastrin-17 was found to decrease MCR (19). Other investigations, however, showed that nonsulfated and sulfated gastrin-17 had the same potency evaluated from plasma concentrations of
the peptides and, therefore, the same MCR (4, 5). Studies in cats supported the conclusion (13). We found that
sulfation of gastrin-6 reduced the MCR, and similar observations were
made from sulfation of BOC-gastrin-6 in cats
(12). But these findings may apply only to small gastrin
peptides. In vitro studies have shown that sulfation of peptides
protects against degradation (16, 19), as recorded in the
present study with gastrin-6. But since ~50% of the immunoreactivity
was still present after incubation for 1 h, enzymatic degradation
in plasma does not contribute significantly to the MCR. Nonsulfated
gastrin-17 had a lower MCR than gastrin-6 because of a different
distribution and extraction in the vascular beds, as recently shown in
pigs (unpublished observations). The difference between the MCR of
sulfated and nonsulfated gastrin-6 was due to the different
Vd. The half-life of the hexapeptides was not significantly
different. This secondary pharmacokinetic parameter depends on the two
primary parameters MCR and Vd through the expression
t1/2 = (0.693 Vd)/MCR. Since
the MCR and Vd both differed to the same extent with a
factor of ~3, a major difference between the half-lives was not to be expected.
We conclude that gastrin-6 has a higher potency but a lower efficacy
than nonsulfated gastrin-17. The efficacy of gastrin-6 was increased by
sulfation, which also reduced the MCR. Since preliminary studies have
identified a specific G cell enzyme active in the processing of
gastrin-6, the peptide should not be regarded merely as a waste
product. In spite of its modest contribution to the pool of circulating
gastrin, gastrin-6 may still contribute to subtle modifications of
gastric acid secretion.
| |
ACKNOWLEDGEMENTS |
The expert technical assistance of Inge Mortensen and Winna
Stavnstrup is gratefully acknowledged.
| |
FOOTNOTES |
The study was supported by grants from the Danish Hospital Foundation,
Region of Copenhagen, the Faroe Islands and Greenland, the Danish
Foundation for the Advancement of Medical Science, the Danish
Biotechnology Program for Signal Peptide Research, and Mogens
Andreassen's Foundation.
Address for reprint requests and other correspondence: C. Palnæs Hansen, Dept. of Gastrointestinal Surgery C, Rigshospitalet, DK-2100 Copenhagen, Denmark.
The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement"
in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 21 January 2000; accepted in final form 13 May 2000.
| |
REFERENCES |
1.
Andersen, BN.
Measurements and occurrence of sulfated gastrins.
Scand J Clin Lab Invest
44:
5-24,
1984.
2.
Baron, JH.
The clinical use of gastric function tests.
Scand J Gastroenterol
5, Suppl6:
9-46,
1970.
3.
Blair, EL,
Hirst BH,
Kay Lund P,
Reed JD,
Sanders DJ,
and
Shaw B.
Gastric acid and pepsin-stimulating activity of nonsulfated fragments of gastrin in the cat.
Digestion
20:
190-200,
1980[ISI][Medline].
4.
Cantor, P,
Boye Petersen M,
Christiansen J,
and
Rehfeld JF.
Does sulfation of gastrin influence gastric acid secretion in man?
Scand J Gastroenterol
25:
739-745,
1990[ISI][Medline].
5.
Cantor, P,
Petronijevic L,
Pedersen JF,
and
Worning H.
Cholecystokinetic and pancreazymic effects of O-sulfated gastrin compared with nonsulfated gastrin and cholecystokinin.
Gastroenterology
91:
1154-1163,
1986[ISI][Medline].
6.
Carter, D,
Taylor I,
Elashoff J,
and
Grossman M.
Reappraisal of the secretory potency and disappearance rate of pure human minigastrin.
Gut
20:
705-708,
1979[Abstract/Free Full Text].
7.
Dowd, JE,
and
Riggs DS.
A comparison of estimates of Michaelis-Menten kinetic constants from various linear transformations.
J Biol Chem
240:
863-869,
1965[Free Full Text].
8.
Eysselein, VE,
Maxwell W,
Reedy T,
Wünsch E,
and
Walsh JH.
Similar acid stimulatory potencies of synthetic human big and little gastrin in man.
J Clin Invest
73:
1284-1290,
1984.
9.
Gregory, H,
Hardy PM,
Jones DS,
Kenner GW,
and
Sheppard RC.
The antral hormone gastrin: structure of gastrin.
Nature
204:
931-933,
1964.
10.
Gregory, RA,
Dockray GJ,
Reeve JR,
Shively JE,
and
Miller C.
Isolation from porcine antral mucosa a hexapeptide corresponding to the C-terminal sequence of gastrin.
Peptides
4:
319-323,
1983[ISI][Medline].
11.
Gregory, RA,
and
Tracy HJ.
The constitution and properties of two gastrins extracted from hog antral mucosa.
Gut
5:
103-117,
1964.
12.
Hirst, BH,
Holland J,
Marr AP,
Parsons ME,
and
Sanders DJ.
Comparison of effect of peptide length and sulfation on acid secretory potency of gastrin in the cat in vivo and in vitro.
J Physiol (Lond)
357:
441-452,
1984[Abstract/Free Full Text].
13.
Hirst, BH,
Reed JD,
Lund PK,
and
Sanders DJ.
Sensitivity of parietal cells to gastrin in the cat: comparison with man and dog.
Digestion
20:
300-306,
1980[ISI][Medline].
14.
Holford, NHG,
and
Sheiner LB.
Understanding the dose-effect relationship. Clinical application of pharmacokinetic-pharmacodynamic models.
Clin Pharmacokinet
6:
429-453,
1981[ISI][Medline].
15.
Huttner, WB,
and
Baeuerle PA.
Protein sulfation on tyrosine.
Modern Cell Biol
6:
97-140,
1988.
16.
Koulischer, D,
Moroder L,
and
Deschodt-Lanckman M.
Degradation of cholecystokinin octapeptide, related fragments and analogs by human and rat plasma in vitro.
Regul Pept
4:
127-139,
1982[ISI][Medline].
17.
Morley, JS,
Tracy HJ,
and
Gregory RA.
Structure-function relationships in the active C-terminal tetrapeptide sequence of gastrin.
Nature
207:
1356-1359,
1965[Medline].
18.
Palnaes Hansen, C,
Stadil F,
and
Rehfeld JF.
Metabolism and influence of gastrin-52 on gastric acid secretion in humans.
Am J Physiol Gastrointest Liver Physiol
269:
G600-G605,
1995[Abstract/Free Full Text].
19.
Pauwels, S,
Dockray GJ,
and
Walker R.
Comparison of the metabolism of sulfated and unsulfated heptadecapeptide gastrin in humans.
Gastroenterology
92:
1120-1225,
1986.
20.
Rehfeld, JF.
Immunochemical studies on cholecystokinin. I. Development of sequence specific radioimmunoassays for porcine triacontapeptide cholecystokinin.
J Biol Chem
253:
4016-4021,
1978[Free Full Text].
21.
Rehfeld, JF.
Accurate measurement of cholecystokinin in plasma.
Clin Chem
44:
991-1001,
1998[Abstract/Free Full Text].
22.
Rehfeld, JF,
Hansen CP,
and
Johnsen AH.
Postpoly(Glu) cleavage and degradation modified by O-sulfated tyrosine: a novel posttranslational processing mechanism.
EMBO J
14:
389-396,
1995[ISI][Medline].
23.
Rehfeld, JF,
and
Johnsen AH.
Identification of gastrin component I as gastrin-71. The largest possible bioactive progastrin product.
Eur J Biochem
223:
765-773,
1994[ISI][Medline].
24.
Rehfeld, JF,
and
Larsson LI.
The predominating molecular form of gastrin and cholecystokinin in the gut is a small peptide corresponding to their COOH-terminal tetrapeptide amide.
Acta Physiol Scand
115:
117-119,
1979.
25.
Rehfeld, JF,
Stadil F,
and
Rubin B.
Production and evaluation of antibodies for the radioimmunoassay of gastrin.
Scand J Clin Lab Invest
30:
221-232,
1972[ISI][Medline].
26.
Rondouin, G,
Coletti-Previero MA,
Descomps B,
and
Previero A.
Sulfonated enkephalin: an active peptide resistant to serum degradative proteolysis.
Neuropeptides
1:
23-28,
1980.
27.
Stadil, F,
and
Rehfeld JF.
Preparation of 125I-labelled synthetic human gastrin I for radioimmunoanalysis.
Scand J Clin Lab Invest
30:
361-368,
1972[ISI][Medline].
28.
Stadil, F,
and
Rehfeld JF.
Determination of gastrin in serum. An evaluation of the reliability of a radioimmunoassay.
Scand J Gastroenterol
8:
101-112,
1973[ISI][Medline].
29.
Takeuchi, K,
Speir GR,
and
Johnson LR.
Mucosal gastrin receptor. IV. Binding specificity.
Am J Physiol Gastrointest Liver Physiol
239:
G395-G399,
1980[Abstract/Free Full Text].
30.
Walsh, JH.
Role of gastrin as a trophic hormone.
Digestion
47:
11-16,
1990.
31.
Walsh, J,
Isenberg J,
Ansfield J,
and
Maxwell V.
Clearance and acid-stimulating action of human big and little gastrins in duodenal ulcer subjects.
J Clin Invest
57:
1125-1131,
1976.
Am J Physiol Gastrointest Liver Physiol 279(5):G903-G909
0193-1857/00 $5.00
Copyright © 2000 the American Physiological Society
TOP
ABSTRACT
INTRODUCTION
