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2
*
Faculty of Nutrition and Department of Animal Science, Texas A&M University, College Station, TX 77843;
Department of Medical Physiology, Texas A&M University System Health Science Center, College Station, TX 77843;
**
Department of Nutritional Sciences, Rutgers University, New Brunswick, NJ 08901; and
Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
2To whom correspondence should be addressed.
 |
ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: • citrulline • enterocytes • metyrapone • cortisol • weaning • pigs
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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). Arginine is the physiologic precursor for the synthesis
of nitric oxide, which has been identified as the
endothelium-dependent relaxing factor, a mediator of immune
responses, a neurotransmitter and a signaling molecule (Bredt and Snyder 1994
). In addition, arginine is an essential amino
acid for young mammals (Visek 1986
) and a conditionally
essential amino acid for adults (Beaumier et al. 1996
).
Furthermore, by serving as an allosteric activator of
N-acetylglutamate synthase, which synthesizes
N-acetylglutamate [an activator of carbamoylphosphate
synthase-I
(CPS-I)],3
and as an immediate precursor of ornithine, arginine is essential for
hepatic detoxification of ammonia via the urea cycle (Meijer et al. 1990
). The crucial metabolic roles of arginine are
emphasized by hyperammonemia, cardiovascular abnormalities,
reproductive dysfunction and impaired wound healing, which are caused
by an arginine deficiency (Wu et al. 2000
). Thus,
intestinal synthesis of citrulline is of great nutritional importance,
particularly under stress conditions such as weaning and illness.
Glutamine and proline are major substrates for intestinal synthesis of
citrulline in pigs (Wu et al. 1994
, Wu 1997
). We recently demonstrated that the synthesis of
citrulline from glutamine was enhanced markedly in enterocytes
(absorptive epithelial cells of the small intestine) from weanling pigs
compared with suckling pigs (Dugan et al. 1995
,
Wu et al. 1994
, Wu 1997
). The pathway for
converting glutamine to citrulline requires the following mitochondrial
enzymes: phosphate-dependent glutaminase (PDG),
pyrroline-5-carboxylase synthase (P5CS), ornithine aminotransferase
(OAT), CPS-I and ornithine carbamoyltransferase (OCT) (Fig. 1
). Intestinal PDG is a kidney-type isozyme (Watford 1993
). An increase in P5CS activity may be responsible for the
enhanced synthesis of citrulline from glutamine in enterocytes of
weanling pigs (Wu et al. 1994
). Despite the metabolic
studies of intestinal citrulline synthesis, little is known about the
regulation of this pathway at the molecular level (Matsuzawa et al. 1994
, Wu 1998
). The availability of cDNAs
for mammalian PDG and urea cycle enzymes (Morris 1992
,
Watford 1993
) and the recent cloning of cDNA for
mammalian P5CS (Aral et al. 1996
) have made it possible
to quantify mRNA levels for all intestinal citrulline-synthetic
enzymes.
|
) and humans (Ganong 1991
). Because glucocorticoids are potent regulators of hepatic
arginine-metabolic enzymes (Morris 1992
) and also
enhance P5CS activity in enterocytes of suckling pigs (Flynn and Wu 1997b
), we hypothesized that a cortisol surge may mediate
the increased expression of intestinal citrulline-synthetic enzymes
during weaning. This hypothesis was tested in the current study using
metyrapone, an inhibitor of adrenal cortisol synthesis in pigs and
other mammals (Sangild et al. 1995
). Furthermore, on the
basis of previous studies with urea cycle enzymes (Morris 1992
, Takiguchi and Mori 1995
), we hypothesized
that transcription is likely the major control mechanism for regulating
the expression of intestinal citrulline-synthetic enzymes and that
changes in the activities of these intestinal enzymes during weaning
may reflect primarily alterations in transcription of the corresponding
genes. Thus, both mRNA levels and activities of intestinal
citrulline-synthetic enzymes were measured in the same pigs as an
initial test of this hypothesis. |
MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Chemicals.
L-[U-14C]glutamate was obtained from American
Radiolabeled Chemicals (St. Louis, MO). Dowex AG 1-X8 (acetate form)
was purchased from Bio-Rad (Richmond, CA). ATP, NADPH and
-ketoglutarate were obtained from Boehringer Mannheim (Indianapolis,
IN). Metyrapone and all other chemicals were purchased from Sigma
Chemical (St. Louis, MO).
Animals.
Pigs were offspring of Yorkshire x Landrace sows and Duroc
x Hampshire boars and housed in the Texas A&M University
Veterinary Research Park. Piglets were freely nursed by their mothers.
At 21 d of age, 24 pigs (5.7 ± 0.28 kg body weight) were
randomly assigned to one of three groups (n = 8
pigs/group). One group was allowed to continue to nurse freely
(unweaned pigs), whereas the other two groups were weaned to a corn and
soybean meal–based diet that met NRC recommended requirements for
nutrients (Flynn and Wu 1997b
). Weanling pigs received
intramuscular injections of vehicle solvent (saline) or metyrapone (5
mg/kg body) 5 min before weaning and 24 and 72 h later. This
period of metyrapone administration corresponded to the cortisol surge
in weanling pigs (Borbolla 1994
). The dose of metyrapone
used was based on previous studies with piglets (Sangild et al. 1995
). Blood samples (3 mL) were obtained from the jugular vein
of pigs immediately before and on d 2 and 8 postsaline or
postmetyrapone administration for the analysis of plasma cortisol using
a cortisol kit (Flynn and Wu 1997b
). At 29 d of
age, pigs were anesthetized and killed by jugular puncture for the
isolation of jejunum, as previously described (Flynn and Wu 1997a
). The jejunum was washed three times with saline to
remove luminal content, and then used for preparing enterocytes
utilizing Ca2+-free Krebs-Henseleit bicarbonate (KHB)
buffer as previously described (Wu et al. 1996
,
Wu 1997
).
Metabolic studies.
Enterocytes (~20 mg protein) were incubated at 37°C for 0 or 30 min
in 2 mL KHB buffer (pH 7.4, saturated with 95% O2/5%
CO2) containing 5 mmol/L glucose, 10 g/L bovine serum
albumin, 20 mmol/L HEPES and 1, 2 or 5 mmol/L glutamine, as previously
described (Wu and Knabe 1995
). Incubations were
terminated by the addition of 0.2 mL of 1.5 mol/L HClO4.
Neutralized extracts were used for analysis of amino acids by HPLC as
previously described (Wu et al. 1994
). Rates of
citrulline synthesis from glutamine were calculated on the basis of
citrulline concentrations in cells plus medium between 0- and 30-min
incubation periods (Wu and Knabe 1995
).
Determination of activities of citrulline-synthetic enzymes.
For determining the activities of PDG, OAT, CPS-I and OCT,
enterocytes (~40 mg protein) were homogenized in 5 mL of ice-cold
medium (300 mmol/L sucrose, 5 mmol/L HEPES, 1 mmol/L EDTA and 3 mmol/L
dithiothreitol; pH 7.4) containing protease inhibitors (5 mg/L
phenylmethylsulfonyl fluoride, 5 mg/L aprotinin, 5 mg/L chymostatin and
5 mg/L pepstatin A) for preparing mitochondria, as previously described
(Wu and Knabe 1995
). Mitochondria were stored at
-80°C for 24 h and then lysed by three cycles of freezing
(liquid nitrogen) and thawing (37°C water bath). Extracts were
centrifuged at 10,000 x g for 10 min at 4°C. The
supernatant fluid was used for determining the activities of PDG, OAT,
CPS-I and OCT at 37°C for 0, 7.5 and 15 min as previously
described (Davis and Wu 1998
, Wu 1995
).
Briefly, the PDG assay mixture (0.2 mL) consisted of 20 mmol/L
L-glutamine, 150 mmol/L potassium phosphate (pH 8.2) and
mitochondrial extracts (0.05 and 0.1 mg protein). The OAT assay mixture
(2 mL) contained 75 mmol/L potassium phosphate buffer (pH 7.5), 20
mmol/L ornithine, 0.45 mmol/L pyridoxal phosphate, 0 or 3.75 mmol/L
-ketoglutarate, 5 mmol/L o-aminobenzaldehyde and
mitochondrial extracts (0.25 and 0.5 mg protein). The CPS-I assay
mixture (0.5 mL) consisted of 0.15 mol/L potassium phosphate buffer (pH
7.5), 30 mmol/L ATP, 25 mmol/L MgCl2, 5 mmol/L
N-acetylglutamate, 20 mmol/L NH4Cl, 5 mmol/L
ornithine, 100 mmol/L NaHCO3, 10 U of OCT and
mitochondrial extracts (0.5 and 1 mg protein). The OCT assay mixture
(0.2 mL) contained 0.1 mol/L potassium phosphate buffer (pH 7.5), 15
mmol/L ornithine, 10 mmol/L carbamoylphosphate and mitochondrial
extracts (0.02 and 0.04 mg protein). For determining P5CS activity,
mitochondria were prepared from enterocytes and used immediately for
enzyme assay at 23°C for 0, 15 and 30 min, as previously described
(Wu and Knabe 1995
). The P5CS assay mixture (1 mL)
contained 20 mmol/L MgCl2, 0.1 mol/L HEPES (pH 7.4), 1
mmol/L gabaculine (an inhibitor of OAT), 1 mmol/L
[U-14C]glutamate (25 Bq/nmol), 3 mmol/L ATP, 0.2 mmol/L
NADPH, 15 mmol/L phosphocreatine, 10 U of creatine kinase,
0.25% Nonidet P-40 and mitochondria (0.5 and 1 mg protein). Enzyme
activities are expressed on the basis of mitochondrial protein, which
was determined using a modified Lowry procedure (Wu et al. 1994
). All enzyme assays were linear with time and with protein
either in mitochondrial extracts (for all enzymes except P5CS) or in
mitochondria (for P5CS).
Determination of mRNA levels for citrulline-synthetic enzymes.
Total RNA was extracted from enterocytes using TRIZOL reagent (GIBCO
BRL, Bethesda, MD) (~2 g cell protein/L TRIZOL). The RNA was
separated on a 0.8% agarose-formaldehyde gel by electrophoresis,
followed by transfer to a positively charged nylon membrane (Amersham
Pharmacia Biotech, Piscataway, NJ) using transfer reagent from Biotecx
(Houston, TX) (Flynn et al. 1999
).
32P-labeled cDNA probes for rat kidney-type PDG
(Banner et al. 1988
), human P5CS (Aral et al. 1996
), human OAT (Mitchell et al. 1988
), rat
CPS-I (Adock and O’Brien 1984
), rat OCT
(Takiguchi et al. 1987
) and mouse cyclophilin (Ambion,
Austin, TX) were generated using the Strip EZ DNA kit from Ambion
according to the manufacturer’s instructions. Hybridizations were
performed at 42°C for 16 h and blots were exposed to Biomax MS
film (Kodak, Rochester, NY) for 24 h at -70°C. Blots were
scanned using a UMAX S6E scanner (UMAX Data Systems, Taiwan) with
VistaScan software (Kodak) and analyzed with Multianalyst (BioRad,
Hercules, CA). Band intensities were normalized on the basis of the
cyclophilin mRNA levels. The relative abundance of each enzyme mRNA was
calculated by dividing the intensity of the mRNA signal for the enzyme
with that of the cyclophilin RNA.
Statistical analysis.
Results were analyzed by one- or two-way (treatment x time or
treatment x glutamine concentration) ANOVA, with the
Student-Newman-Keuls test for multiple comparison of means
(Steel and Torrie 1980
). Probability < 0.05 was
taken to indicate statistical significance.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Plasma concentrations of cortisol were 285% greater
(P < 0.01) in weanling pigs on d 2 postweaning
compared with unweaned pigs, and returned to preweaning levels on d 8
postweaning (Table 1
). Metyrapone administration to weanling pigs abolished the increase in
plasma concentrations of cortisol on d 2 postweaning (Table 1)
.
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Increasing medium glutamine concentrations from 1 to 5 mmol/L increased
(P < 0.01) citrulline synthesis in a
concentration-dependent manner in unweaned and weanling pigs
(Table 2
). Rates of synthesis of citrulline from glutamine were ~10-fold
higher (P < 0.01) in enterocytes of weanling pigs
compared with unweaned pigs. Prevention of the cortisol surge by
metyrapone administration eliminated the difference in citrulline
synthesis between weanling and unweaned pigs (Table 2)
.
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Table 3
summarizes relative differences in the activities of
citrulline-synthetic enzymes in enterocytes. The activities of PDG
and P5CS were 38 and 720% higher (P < 0.01),
respectively, in enterocytes of weanling pigs compared with unweaned
pigs, but there were no differences (P > 0.05) in the
activities of OAT, CPS-I and OCT between unweaned and weanling
pigs. Metyrapone administration to weanling pigs abolished
(P < 0.01) the increase in P5CS activity and had no
effect (P > 0.05) on the activities of PDG, CPS-I
and OCT. Intestinal OAT activity was 30% higher (P < 0.01) in metyrapone-treated weanling pigs compared with untreated
weanling pigs.
|
Relative abundance of mRNA levels for intestinal
citrulline-synthetic enzymes (normalized on the basis of
cyclophilin mRNA) is shown in Table 3
and Figure 2
. The mRNA levels for PDG, P5CS, OAT and OCT were 139, 157, 102 and 55%
higher (P < 0.01), respectively, in enterocytes of
weanling pigs compared with unweaned pigs. There were no differences
(P > 0.05) in the mRNA levels for CPS-I between
unweaned and weanling pigs. Metyrapone administration to weanling pigs
abolished the increase in P5CS mRNA levels and had no effect
(P > 0.05) on PDG mRNA levels. Interestingly, the mRNA
levels for OAT and OCT were 216 and 39% higher, respectively, in
metyrapone-treated weanling pigs compared with untreated weanling
pigs. Although some changes in mRNA levels (e.g., OCT) were
significant, they may not be of biological importance due to the
semiquantitative nature of Northern blots.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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). In addition, we found that a
cortisol surge was associated with increased intestinal P5CS activity
during weaning, which could be abolished by administration of RU486
(mifepristone; a glucocorticoid receptor antagonist) to weanling pigs
(Flynn and Wu 1997b
). Collectively these studies suggest
an important role for cortisol in regulating intestinal P5CS expression
and citrulline synthesis during weaning. Results of the current study
provide additional evidence to indicate that increased activity of P5CS
is responsible for the increased capacity of enterocytes for citrulline
synthesis from glutamine in weanling piglets (Tables 2
and 3)
.
Furthermore, the associated increases in P5CS mRNA abundance indicate
that the increased P5CS activity is due primarily to regulation at the
pretranslational level, probably via increased transcription of the
P5CS gene. Relative increases in P5CS activity and mRNA abundance were
not precisely identical (Table 3)
, possibly as a consequence of
significant differences in half-lives and therefore in induction
profiles between P5CS protein and its mRNA (Hargrove and Schmidt 1989
, Hargrove 1993
). For example, P5CS mRNA may
have peaked at a higher level before d 8 postweaning and begun to
decline, whereas P5CS protein and enzyme activity, as a result of its
longer half-life, would decline more slowly and thus remain at a
higher relative level than its mRNA at d 8 postweaning. Alternatively,
the higher relative level of P5CS activity might reflect a modest
increase in half-life of P5CS protein or increased translational
efficiency of P5CS mRNA. Nonetheless, these considerations do not alter
the principal conclusion that increased levels of P5CS mRNA are
primarily responsible for the increased P5CS activity. To substantiate our suggestion that the increased P5CS activity in enterocytes of weanling piglets largely reflects increased levels of P5CS mRNA, additional data on the P5CS protein and its half-life would be desirable. However, such information cannot be obtained at the present time because the appropriate antibody is not available. Even if the antibody were available, determination of the half-life of P5CS is not feasible with whole piglets and also cannot be accomplished with the short-term incubation of enterocytes used here. In addition, although measurements of P5CS transcription rates would be useful, they are not essential for the conclusions of this study. In any case, we wish to note that precise methods to measure transcription rates in porcine enterocytes have not been established and also would require cloning of porcine P5CS cDNA. This is because the conditions for measurement of transcription rates are more stringent than for Northern blotting, where it is possible to use homologous (but not identical) cDNAs from related species.
Activities of the other enzymes in the citrulline biosynthetic pathway
exhibited little or no change during weaning, despite the fact that,
with the exception of CPS-I, there were some increases in relative
abundance of the corresponding mRNAs (Table 3)
. As in the case of P5CS,
these modest discrepancies could simply reflect differences in
half-lives of the mRNAs and proteins, indicating that 8 d is
an insufficient period of time for the enzyme levels to reflect
increases in mRNA levels. This explanation is entirely possible because
some of these enzymes have half-lives on the order of days [e.g.,
4 d for rat renal OAT (Kobayashi et al. 1976
) and
3–9 d for rat liver urea-cycle enzymes and OAT (Fagan et al. 1991
, Morris 1992
, Mueckler et al. 1983
)]. The lack of CPS-I or OCT induction in pig
enterocytes during weaning is in agreement with previous studies
demonstrating that intestinal expression of these enzymes in rats is
not inducible by glucocorticoids (Ryall et al. 1986
,
Wraight et al. 1985
).
Metyrapone, an inhibitor of adrenal cortisol synthesis (Sangild et al. 1995
), prevented a cortisol surge in weanling pigs
(Table 1)
. Thus, metyrapone administration to weanling pigs provides a
useful tool to determine whether cortisol plays a role in mediating the
enhanced expression of citrulline-synthetic enzymes. A novel
finding of this study is that metyrapone administration to weanling
pigs completely prevented the increase in both mRNA levels and activity
of intestinal P5CS (Table 3)
. This result suggests an essential role
for a cortisol surge in mediating the enhanced expression of intestinal
P5CS during weaning. In contrast, metyrapone treatment could not
prevent the weaning-associated increases in mRNA levels for
intestinal PDG (Table 3)
, suggesting that factors other than cortisol
may play an important role in enhancing its mRNA levels during weaning.
Interestingly, metyrapone administration to weanling pigs resulted in
increased mRNA levels for intestinal OAT and OCT (Table 3)
. It is
likely that these mRNAs are responding to increased levels of a
different hormone whose action on expression of these enzymes normally
is antagonized by the cortisol surge during weaning at this stage of
development.
Consistent with the prevention of the induction of intestinal P5CS,
metyrapone administration to weanling pigs abolished the increase in
intestinal synthesis of citrulline from glutamine (Table 2)
. This
result provides another line of evidence supporting the notion that
P5CS is a key regulatory enzyme in the synthesis of citrulline from
glutamine (Wu et al. 1994
). Our finding also provides a
molecular basis for the induction of citrulline synthesis in
enterocytes of weanling pigs, which is of nutritional importance for
enhancing endogenous synthesis of arginine (Wu and Morris 1998
). In addition to glutamine, proline is an important
substrate for citrulline synthesis in pig enterocytes (Wu 1997
). We found that the synthesis of citrulline from proline
increased by 26% in enterocytes of 29-d-old weaned pigs compared with
age-matched unweaned pigs, probably due to increased proline
oxidase activity (G. Wu, unpublished data). Because cortisol is a
potent inducer of expression of intestinal P5CS, whose activity
decreases markedly during the first 3 wk after birth (Wu et al. 1994
, Wu and Knabe 1995
), cortisol
administration to 7- to 21-d-old suckling pigs may prevent the marked
decline in intestinal synthesis of citrulline from glutamine (Wu et al. 1995
). This hormonal intervention may help improve
arginine nutrition in the sow-reared piglets, which exhibit an
arginine deficiency at d 7 to 21 of life (Flynn et al. 2000
).
In summary, our studies indicate the following: 1) increased P5CS activity is responsible for the increased cellular capacity for intestinal synthesis of citrulline from glutamine in weaning pigs; 2) the increased P5CS activity largely reflects increased levels of P5CS mRNA, probably due to increased transcription of the P5CS gene; and 3) these increases are mediated by a cortisol surge during weaning that can be blocked by metyrapone administration.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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3 Abbreviations used: CPS-I, carbamoyl-phosphate synthase-I; CYPH, cyclophilin; KHB, Krebs-Henseleit bicarbonate; OAT, ornithine aminotransferase; OCT, ornithine carbamoyltransferase; P5CS, pyrroline-5-carboxylate synthase; PDG, phosphate-dependent glutaminase.
Manuscript received January 21, 2000. Initial review completed March 3, 2000. Revision accepted March 29, 2000.
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REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
1.
Adcock M. S., O’Brien W. E. Molecular cloning of cDNA for rat and human carbamyl phosphate synthetase I. J. Biol. Chem. 1984;259:13471-13476
2.
Aral B., Schlenzig J.-S., Liu G., Kamoun P. Database cloning human 
1-pyrroline-5-carboxylate synthetase (P5CS) cDNA: a bifunctional enzyme catalyzing the first 2 steps in proline biosynthesis. C.R. Acad. Sci. Paris. 1996;319:171-178
3. Banner C., Hwang J.-J., Shapiro R. A., Wenthold R. J., Nakatani Y., Lampel K. A., Thomas J., Huie D., Curthoys N. P. Isolation of a cDNA to rat brain glutaminase. Mol. Brain Res. 1988;3:247-254
4. Beaumier L., Castillo L., Yu Y.-M., Ajami A. M., Young V. R. Arginine: new and exciting developments for an "old" amino acid. Biomed. Environ. Sci. 1996;9:296-315[Medline]
5. Borbolla A. G. Utilization of Nutrients by the Small Intestine of the Developing Pig and the Role of Corticosteroids in Post-Weaning Lag in Pigs 1994 Doctoral thesis Texas A&M University, College Station, TX.
6. Bredt D. S., Snyder S. H. Nitric oxide: a physiological messenger molecule. Annu. Rev. Biochem. 1994;63:175-195[Medline]
7. Davis P. K., Wu G. Compartmentation and kinetics of urea cycle enzymes in porcine enterocytes. Comp. Biochem. Physiol. 1998;119B:527-537
8. Dugan M.E.R., Knabe D. A., Wu G. The induction of citrulline synthesis from glutamine in enterocytes of weaned pigs is not due primarily to age or change in diet. J. Nutr. 1995;125:2388-2393
9.
Fagan R. J., Lazaris-Karatzas A., Sonenberg N., Rozen R. Translational control of ornithine aminotransferase. Modulation by initiation factor eIF-4E. J. Biol. Chem. 1991;266:16518-16523
10. Flynn, N. E., Knabe, D. A., Mallick, B. K. & Wu, G. (2000) Postnatal changes of plasma amino acids in suckling pigs. J. Anim. Sci. (in press).
11.
Flynn N. E., Meininger C. J., Kelly K., Ing N. H., Morris S. M., Jr, Wu G. Glucocorticoids mediate the enhanced expression of intestinal type II arginase and argininosuccinate synthase in postweaning pigs. J. Nutr. 1999;129:799-803
12.
Flynn N. E., Wu G. Enhanced metabolism of arginine and glutamine in enterocytes of cortisol-treated pigs. Am. J. Physiol. 1997a;272:G474-G480
13.
Flynn N. E., Wu G. Glucocorticoids play an important role in mediating the enhanced metabolism of arginine and glutamine in enterocytes of postweaning pigs. J. Nutr. 1997b;127:732-737
14. Ganong W. F. Review of Medical Physiology 15th ed. 1991:340 Appleton & Lange Norwalk, CT.
15. Hargrove J. L. Microcomputer-assisted kinetic modeling of mammalian gene expression. FASEB J 1993;7:1163-1170[Abstract]
16. Hargrove J. L., Schmidt F. H. The role of mRNA and protein stability in gene expression. FASEB J 1989;3:2360-2370[Abstract]
17.
Kobayashi K., Kito K., Katunuma N. Effects of estrogen on the turnover rates of ornithine aminotransferase in rat liver and kidney. J. Biochem. 1976;79:787-793
18.
Matsuzawa T., Kobayashi T., Tashiro K., Kasahara M. Changes in ornithine metabolic enzymes induced by dietary protein in small intestine and liver: intestine-liver relationship in ornithine supply to liver. J. Biochem. 1994;116:721-727
19.
Meijer A. J., Lamers W. H., Chamuleau A.F.M. Nitrogen metabolism and ornithine cycle function. Physiol. Rev. 1990;70:701-748
20.
Mitchell G. A., Looney J. E., Brody L. C., Steel G., Suchanek M., Engelhardt J. F., Willard H. F., Valle D. Human ornithine-
-aminotransferase. J. Biol. Chem. 1988;263:14288-14295
21. Morris S. M., Jr Regulation of enzymes of urea and arginine synthesis. Annu. Rev. Nutr. 1992;12:81-101[Medline]
22.
Mueckler M. M., Merrill M. J., Pitot H. C. Translational and pretranslational control of ornithine aminotransferase synthesis in rat liver. J. Biol. Chem. 1983;258:6109-6114
23. Ryall J. C., Quantz M. A., Shore G. C. Rat liver and intestinal mucosa differ in the developmental pattern and hormonal regulation of carbamoylphosphate synthetase I and ornithine carbamoyltransferase gene expression. Eur. J. Biochem. 1986;156:453-458[Medline]
24. Sangild P. T., Hilsted L., Nexo E., Fowden A. L., Silver M. Vaginal birth versus elective caesarean section: effects on gastric function in the neonate. Exp. Physiol. 1995;80:147-157[Abstract]
25. Steel R.G.D., Torrie J. H. Principles and Procedures of Statistics 1980 McGraw Hill New York, NY.
26. Takiguchi M., Mori M. Transcriptional regulation of genes for ornithine cycle enzymes. Biochem. J. 1995;312:649-659
27.
Takiguchi M., Murakami T., Miura S., Mori M. Structure of the rat ornithine carbamoyltransferase gene, a large, X chromosone-linked gene with an atypical promoter. Proc. Natl. Acad. Sci. U.S.A. 1987;84:6136-6140
28. Visek W. J. Arginine needs, physiological state and usual diets. A reevaluation. J. Nutr. 1986;116:36-46
29. Watford M. Hepatic glutaminase expression: relationship to kidney-type glutaminase and to the urea cycle. FASEB J 1993;7:1468-1474[Abstract]
30. Worsae H., Schmidt M. Plasma cortisol and behaviour in early weaned piglets. Acta Vet. Scand. 1980;21:640-657[Medline]
31. Wraight C., Lingelbach K., Hoogenraad N. Comparison of ornithine transcarbamylase from rat liver and intestine. Evidence for differential regulation of enzyme levels. Eur. J. Biochem. 1985;153:239-242[Medline]
32. Wu G. Urea synthesis in enterocytes of developing pigs. Biochem. J. 1995;312:717-723
33.
Wu G. Synthesis of citrulline and arginine from proline in enterocytes of postnatal pigs. Am. J. Physiol. 1997;272:G1382-G1390
34.
Wu G. Intestinal mucosal amino acid catabolism. J. Nutr. 1998;128:1249-1252
35.
Wu G., Knabe D. A. Arginine synthesis in enterocytes of neonatal pigs. Am. J. Physiol. 1995;269:R621-R629
36. Wu G., Knabe D. A., Flynn N. E. Synthesis of citrulline from glutamine in pig enterocytes. Biochem. J. 1994;299:115-121
37.
Wu G., Knabe D. A., Flynn N. E., Yan W., Flynn S. P. Arginine degradation in developing porcine enterocytes. Am. J. Physiol. 1996;271:G913-G919
38.
Wu G., Knabe D. A., Yan W., Flynn N. E. Glutamine and glucose metabolism in enterocytes of the neonatal pig. Am. J. Physiol. 1995;268:R334-R342
39. Wu G., Meininger C. J., Knabe D. A., Bazer F. W., Rhoads J. M. Arginine nutrition in development, health and disease. Curr. Opin. Clin. Nutr. Metab. Care 2000;3:59-66[Medline]
40. Wu G., Morris S. M., Jr Arginine metabolism: nitric oxide and beyond. Biochem J 1998;336:1-17
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