Faculty of Nutrition and Departments of 1 Animal Science, 2 Veterinary Anatomy and Public Health, and 3 Medical Physiology, Texas A&M University, College Station, Texas 77843
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
This study was conducted to determine a role for cortisol in regulating intestinal ornithine decarboxylase (ODC) activity and to identify the metabolic sources of ornithine for intestinal polyamine synthesis in suckling pigs. Thirty-two 21-day-old suckling pigs were randomly assigned to one of four groups with eight animals each and received daily intramuscular injections of vehicle solution (sesame oil; control), hydrocortisone 21-acetate (HYD; 25 mg/kg body wt), RU-486 (10 mg/kg body wt, a potent blocker of glucocorticoid receptors), or HYD plus RU-486 for two consecutive days. At 29 days of age, pigs were killed for preparation of jejunal enterocytes. The cytosolic fraction was prepared for determining ODC activity. For metabolic studies, enterocytes were incubated for 45 min at 37°C in 2 ml of Krebs-bicarbonate buffer (pH 7.4) containing 1 mM [U-14C]arginine, 1 mM [U-14C]ornithine, 1 mM [U-14C]glutamine, or 1 mM [U-14C]proline plus 1 mM glutamine. Cortisol administration increased intestinal ODC activity by 230%, polyamine (putrescine, spermidine, and spermine) synthesis from ornithine and proline by 75-180%, and intracellular polyamine concentrations by 45-83%. Polyamine synthesis from arginine was not detected in enterocytes of control pigs but was induced in cells of cortisol-treated pigs. There was no detectable synthesis of polyamines from glutamine in enterocytes of all groups of pigs. The stimulating effects of cortisol on intestinal ODC activity and polyamine synthesis were abolished by coadministration of RU-486. Our data indicate that an increase in plasma cortisol concentrations stimulates intestinal polyamine synthesis via a glucocorticoid receptor-mediated mechanism and that proline (an abundant amino acid in milk) is a major source of ornithine for intestinal polyamine synthesis in suckling neonates.
amino acids; ornithine decarboxylase
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
POLYAMINES (putrescine, spermidine, and spermine) are essential to the proliferation, differentiation, and migration of mammalian cells, including intestinal epithelial cells (17). Ornithine decarboxylase (ODC) is the first and key regulatory enzyme in polyamine synthesis from ornithine (23). Intestinal ODC expression is induced in early weaned animals, including rats (19) and pigs (37), which may play a role in intestinal maturation and remodeling. Glucocorticoids, whose plasma concentrations are markedly increased in weanling animals [e.g., rats (16) and pigs (31)], may play an important role in regulating intestinal ODC activity during weaning. To test this hypothesis, Nsi-Emvo et al. (22) determined the effect of cortisol (hydrocortisone) administration on intestinal ODC activity in 12-day-old suckling rats so as to eliminate the confounding effects of weaning, stress, and feeding. Despite the foregoing, little information is available on the effect of glucocorticoids on intestinal polyamine synthesis in the neonatal pig, an excellent animal model for studying infant intestinal physiology and metabolism (6, 25, 37). Also, we were not aware of studies to determine the effects of glucocorticoids on intestinal ODC activity or polyamine synthesis in pigs.
An increase in enzyme activity measured under in vitro assay conditions does not necessarily indicate an enhanced metabolic flux or product formation in intact cells (12). Thus both ODC activity and polyamine synthesis should be determined in enterocytes of cortisol-treated suckling animals so as to establish its role in enhancing intracellular provision of polyamines. Arginase is generally assumed to be a major source of ornithine for polyamine synthesis in mammalian cells (39). However, intestinal arginase activity is negligible in suckling animals, including pigs (37). In addition, ornithine is negligible in milk, including human and sow's milk (9, 34), and there is little uptake of ornithine from arterial blood by the small intestine (33). Thus potential metabolic sources of the ornithine for intestinal polyamine synthesis remain unknown. Our recent studies have identified proline and glutamine [abundant amino acids in milk (9, 34)] as major substrates for ornithine synthesis in enterocyte mitochondria of suckling pigs (32, 36). However, it is not known whether ornithine generated from proline and glutamine in mitochondria can be used for polyamine synthesis in the cytosol.
In view of the foregoing, the objectives of this study were to determine whether glucocorticoids increase intestinal ODC activity and polyamine synthesis in suckling pigs and to identify potential metabolic sources of ornithine for polyamine synthesis in enterocytes. Our results demonstrate that an increase in plasma cortisol concentrations stimulates intestinal polyamine synthesis via a glucocorticoid receptor-mediated mechanism and that proline is the major source of ornithine for intestinal polyamine synthesis in suckling neonates.
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
This study was carried out in accordance with the guidelines of the United States Research Council for the care and use of animals and was approved by the Texas A&M University Institutional Animal Care Committee.
Chemicals.
HPLC-grade methanol and water were purchased from Fisher Scientific
(Houston, TX). L-[U-14C]ornithine,
L-[U-14C]arginine,
L-[U-14C]proline, and
L-[U-14C]glutamine were obtained from
American Radiolabeled Chemicals (St. Louis, MO). Hydrocortisone
21-acetate (HYD), RU-486 [mifepristone; 17--hydroxy-11
-(4-dimethylaminophenyl)17
-(prop-1-ynyl)estra-4,9-dien-3-one], and all other chemicals used were purchased from Sigma Chemical (St.
Louis, MO).
Animals. Pigs were offspring of Yorkshire × Landrace sows and Duroc × Hampshire boars and were maintained at the Texas A&M University Veterinary Research Park. At 21 days of age, 32 suckling pigs (~5.5 kg) were randomly assigned within litter to one of four groups with eight animals each and received daily intramuscular injections of vehicle solvent (sesame oil; control), HYD (25 mg/kg body wt), RU-486 (10 mg/kg body wt), or HYD plus RU-486 (same doses) for two consecutive days. The HYD administration was chosen to mimic a cortisol surge in piglets during the first 2 days postweaning (15, 31). Cortisol was used because it is the major circulating glucocorticoid in pigs (31). This dose of HYD was selected because it has been reported to increase 1) disaccharidase activities and growth of the small intestine (8) and 2) intestinal glutamine and arginine metabolism (14) in suckling pigs. The dose of RU-486 [a potent blocker of glucocorticoid receptors (3)] was based on previous in vivo studies with a number of species, including rats, humans, and guinea pigs (3) as well as piglets (13-15). Immediately before cortisol or RU-486 administration, and at days 2 and 8 after the administration, blood was obtained from the jugular vein for measuring cortisol concentrations using a cortisol kit (15). After blood collection at 29 days of age, pigs were killed between 10:00 and 11:00 AM to obtain the whole small intestine. Small intestine weights and lengths were measured after intestinal contents were thoroughly removed with saline. Preliminary studies indicated that the responses of ODC activity and polyamine synthesis to cortisol treatment were similar between jejunal and ileal enterocytes in suckling pigs. Thus, because the present work was labor and resource intensive, we concluded that it was not necessary to study all segments of the small intestine from control and cortisol-treated piglets. We chose jejunum in this study, because most of the previous studies on intestinal amino acid metabolism were performed with jejunal enterocytes (18, 35-37) and jejunum constitutes most of the small intestine. During the entire experimental period, suckling piglets were nursed by sows and did not consume the feed provided for the sows. The feeder design prevented the access of piglets to sow's diet.
Preparation and incubation of jejunal enterocytes. The jejunum was washed three times with saline to remove luminal contents and then was used for preparing enterocytes with the use of oxygenated (95% O2-5% CO2) Ca2+-free Krebs-Henseleit bicarbonate (KHB) buffer (pH 7.4) containing 5 mM glucose as previously described (35-37). Cells (25 mg protein/ml) were incubated for 0 or 45 min at 37°C in 2 ml of oxygenated (95% O2-5% CO2) KHB buffer containing 1 mM L-methionine and one of the following: 1) 1 mM L-arginine plus 2 µCi L-[U-14C]arginine, 2) 1 mM L-ornithine plus 2 µCi L-[U-14C]ornithine, 3) 1 mM L-glutamine plus 2 µCi L-[U-14C]glutamine, or 4) 1 mM L-proline plus 2 µCi L-[U-14C]proline plus 1 mM glutamine. Methionine was used as the precursor for S-adenosylmethionine, and subsequently S-decarboxylated 5-adenosylmethionine was used for spermidine and spermine syntheses (23). Glutamate, derived from glutamine by mitochondrial phosphate-dependent glutaminase, was required to convert proline-derived pyrroline-5-carboxylate (P5C) into ornithine by ornithine aminotransferase (32); therefore, glutamine was added to the incubation medium containing L-[U-14C]proline. In keeping with this notion, we found in our preliminary studies that there was little synthesis of [14C]putrescine, spermidine, or spermine from L-[U-14C]proline in pig enterocytes when glutamine or glutamate was not added to the incubation medium. 14C-labeled substrates were used to improve the sensitivity of detecting polyamine synthesis in enterocytes. Incubations were terminated by addition of 0.2 ml of 1.5 M HClO4, and the acidified medium was neutralized with 0.1 ml of 2 M K2CO3 (35). The neutralized extracts were used for analyses of amino acids by an HPLC method involving precolumn derivatization with o-phthaldialdehyde (34) and of 14C-labeled polyamines (see below). Net production of [14C]ornithine was measured by determining the accumulation of [14C]ornithine in cells plus incubation medium, as previously described (32). Incubated enterocytes remained viable for 45 min on the basis of linear consumption of O2, as determined with the use of Clark-type polarographic O2 probes (35-37).
Analysis of polyamines and 14C-polyamines. Polyamine concentrations were determined in freshly isolated enterocytes as described by Wu et al. (40). Briefly, cells (10 mg protein) were acidified with 1 ml of 1.5 M HClO4 and were neutralized with 0.5 ml of 2 M K2CO3. The neutralized extracts were used for polyamine analysis by an ion-pairing HPLC method involving precolumn derivatization with o-phthaldialdehyde. The assay mixture contained 150 µl sample and 10 µl of 1.2% benzoic acid (in 40 mM sodium borate, pH 9.5). An aliquot (100 µl) of the assay mixture was derivatized in an autosampler (model 712 WISP, Waters, Milford, MA) with 100 µl of 30 mM o-phthaldialdehyde (in 3.1% Brij-35, 50 mM 2-mercaptoethanol, and 40 mM sodium borate, pH 9.5), and 100 µl of the derivatized mixture was injected in a Supelco 3-µm reversed-phase C18 column (150 × 4.6 mm ID). Polyamines were separated using a solvent gradient consisting of solution A (0.1 M sodium acetate, 2 mM SDS, 0.5% tetrahydrofuran, and 9% methanol, pH 7.2) and solution B (methanol and 2 mM SDS). Putrescine, spermidine, and spermine in samples were quantified on the basis of authentic standards. In our preliminary studies, we found that, in pig enterocytes incubated at 37°C in the presence of 1 mM ornithine or 1 mM proline plus 1 mM glutamine, cellular concentrations of putrescine were decreased by 12-15% at the end of a 45-min incubation period compared with the values for freshly isolated cells, and there were few differences in cellular concentrations of spermidine or spermine between freshly isolated and incubated cells.
For determining [14C]putrescine, [14C]spermidine, and [14C]spermine, neutralized extracts (2 ml) of enterocytes plus incubation medium were freeze-dried and suspended in 0.3 ml of HPLC H2O. Polyamines were separated by the HPLC method as described above, and the fractions containing [14C]putrescine, [14C]spermidine, and [14C]spermine were collected from the HPLC column for measuring radioactivities by a Packard liquid scintillation counter (Meriden, CT). Blank (0 min incubation) radioactivities were subtracted from sample values. Rates of production of putrescine, spermidine, and spermine were calculated on the basis of intracellular specific activities of [14C]ornithine, which were measured as described by Wu (32).Determination of ODC activity. The cytosolic fraction of enterocytes was prepared and used for measuring ODC activity using 0.2 mM [1-14C]ornithine (37). Briefly, enterocytes (20 mg protein) were homogenized with the use of a glass homogenizer in 2 ml of 50 mM sodium phosphate buffer (pH 7.2) containing 0.2 mM pyridoxal 5-phosphate, 1 mM EDTA, 2.5 mM dithiothreitol, 150 mM sucrose, and protease inhibitors (5 µg/ml phenylmethylsulfonyl fluoride, 5 µg/ml aprotinin, 5 µg/ml chymostatin, and 5 µg/ml pepstatin A). The homogenates were centrifuged at 13,000 g for 15 min at 4°C. The supernatant (free of mitochondria) was used for ODC assay. The assay mixture (0.5 ml) consisted of 0.2 mM L-[1-14C]ornithine (104 dpm/nmol), 0.2 mM pyridoxal 5-phosphate, 0.2 mM EDTA, 0.5 mM dithiothreitol, enzyme preparations (~1 mg protein), and 50 mM sodium phosphate buffer (pH 7.2). Radioactivity blanks containing [1-14C]ornithine but no enzyme preparations were run along with the samples. After incubation at 37°C for 1 h, 14CO2 was collected in 0.2 ml NCS-II, a tissue solubilizer (Amersham, Arlington Heights, IL), and its radioactivity was measured by a liquid scintillation counter.
Examination of intestinal morphology. Villus height, crypt depth, and lamina propria depth in jejunum and ileum were measured in a masked manner, as described by Wu et al. (38), except that intestinal tissues were fixed with 4% paraformaldehyde. Briefly, jejunal samples (3-5 cm long) were split along the mesentery, pinned flat with toothpicks (lumen facing up) to balsa wood, and immersed (lumen facing down) in a 4% paraformaldehyde solution. After 24 h, jejunal samples were removed from the fixative and washed three times with 70% ethanol before being embedded in paraffin. Four cross-sections (6 µm thick) per sample were stained with hematoxylin and eosin. Villus height, crypt depth, and lamina propria depth were measured in villi with well-defined tips and well-attached lamina propria. The lamina propria is an underlying connective tissue layer on which the epithelium of the small intestine rests. The lamina propria depth measurements extended from the base of the villus to the muscularis mucosae.
Milk consumption. Milk consumption was estimated by the weigh-suckle-weigh technique (21) using an additional 24 21-day-old suckling piglets. Piglets were randomly assigned within litter to one of four groups (6 pigs/group) and were treated with vehicle solution, cortisol, RU-486, or cortisol plus RU-486 as described above. At days 1, 4, and 7 postcortisol or -RU-486 administration, body weights of piglets were measured before and after suckling every 1.5 h during a 12-h period from 8:00 AM to 8:00 PM to estimate milk intake.
Determination of protein. Protein in enterocytes and the cytosolic fraction was determined by a modified Lowry procedure with BSA as a standard (36). Briefly, 1 ml of diluted enterocyte suspensions (25-100 µg protein/ml) or BSA standard (0-100 µg/ml) was incubated with 3 ml of an alkali solution (2% Na2CO3, 0.4% NaOH, 0.16% potassium sodium tartrate, and 0.026% CuSO4) for 3 min at room temperature, followed by addition of 0.3 ml of the diluted (1:1) phenol reagent (Sigma Chemical). After incubation for 45 min at room temperature, absorbance of the solution at 660 nm was measured by a UV/VIS spectrophotometer.
Statistical analysis. Data were analyzed by one-way ANOVA and the Student-Newman-Keul's multiple comparison test (28). Probability values < 0.05 were taken to indicate statistical significance.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Milk consumption.
At days 1, 4, and 7 postcortisol or
-RU-486 administration, milk consumption did not differ
(P > 0.05) among the four groups of pigs. Thus data
from each day of the measurements were pooled. Milk consumption by pigs
was 189 ± 15, 183 ± 12, and 177 ± 14 ml · kg
body wt1 · day
1 (means ± SE,
n = 24), respectively, at days 1,
4, and 7 postcortisol or -RU-486 treatment.
Plasma cortisol concentrations.
Figure 1 illustrates plasma cortisol
concentrations in suckling piglets treated with or without cortisol or
RU-486. Cortisol administration to 21-day-old suckling pigs for two
consecutive days markedly increased (P < 0.01) plasma
cortisol concentrations at day 2 posttreatment. At day
8 postcortisol administration, plasma concentrations of cortisol
did not differ (P > 0.05) between control and
HYD-treated piglets. Administration of RU-486 alone increased
(P < 0.01) plasma cortisol concentrations at day
2 posttreatment compared with control pigs. At day 8 post-RU-486 administration, plasma cortisol concentrations were higher
(P < 0.01) in RU-486-treated pigs compared with pigs
not treated with RU-486.
|
Body and small intestine weights.
Cortisol treatment had no effect (P > 0.05) on body
weights in 29-day-old suckling piglets (Table
1). However, small intestine weights were
14% greater (P < 0.05) in cortisol-treated piglets compared with control piglets. Coadministration of RU-486 prevented the
stimulating effect of cortisol on small intestine growth.
|
Jejunal morphology.
Cortisol treatment increased (P < 0.05) jejunal villus
heights by 13% but had no significant effect (P > 0.05) on jejunal crypt depth or lamina propria depth (Table
2). Coadministration of RU-486 prevented
the cortisol-induced increase in jejunal villus heights and had no
effect (P > 0.05) on jejunal crypt depth and laminar
propria depth.
|
Effects of cortisol administration on ODC activity.
Cortisol treatment increased (P < 0.01) enterocyte ODC
activity by 230% (Fig. 2). RU-486
administration alone had no effect (P > 0.05) on ODC
activity compared with control pigs. However, coadministration of
RU-486 with cortisol abolished the stimulating effect of cortisol on
enterocyte ODC activity.
|
Effects of cortisol administration on polyamine synthesis.
Synthesis of putrescine, spermidine, and spermine in enterocytes is
shown in Table 3. Cortisol treatment
increased (P < 0.01) the synthesis of putrescine,
spermidine, and spermine from ornithine by 75-180% in enterocytes
of suckling piglets. Polyamine synthesis from proline was also enhanced
(P < 0.01) in enterocytes of cortisol-treated piglets
compared with control pigs. Polyamine synthesis from arginine was not
detectable in enterocytes of suckling piglets but was induced in cells
of cortisol-treated pigs. In pig enterocytes, spermidine was the major
polyamine formed from ornithine, arginine, and proline. There was no
detectable synthesis of polyamines from glutamine in enterocytes of all
groups of pigs studied. Coadministration of RU-486 abolished the
stimulating effect of cortisol on intestinal polyamine synthesis from
ornithine, arginine, and proline in piglets.
|
Effects of cortisol administration on polyamine concentrations.
Figure 3 summarizes intracellular
concentrations of putrescine, spermidine, and spermine in enterocytes
of pigs treated with or without cortisol or RU-486. In enterocytes of
all groups of pigs studied, the concentration of spermidine was
highest, followed by spermine and putrescine. Cortisol treatment
increased (P < 0.05) polyamine concentrations by
45-83%. RU-486 administration alone had no effect
(P > 0.05) on intestinal polyamine concentrations. However, coadministration of RU-486 prevented the increase in enterocyte polyamine concentrations in cortisol-treated piglets. The
ratios of putrescine to spermidine to spermine were 1:4.2:2.9, 1:3.2:2.5, 1:4.4:3.1, and 1:4.9:3.4 for control, cortisol-treated, RU-486-treated, and cortisol- plus RU-486-treated pigs, respectively.
|
Production of ornithine from arginine, proline, and glutamine in
enterocytes.
Large amounts of ornithine were generated from proline in enterocytes
of both control and cortisol-treated piglets (Fig.
4). Net production of ornithine from
arginine was low in enterocytes of control piglets but was enhanced
~10-fold in cortisol-treated piglets. Net production of ornithine
from glutamine was much lower (P < 0.01) than that
from proline in pig enterocytes. RU-486 treatment prevented the
increase in ornithine production from arginine, but not from proline,
in enterocytes of cortisol-treated pigs.
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Effect of cortisol administration on intestinal polyamine synthesis. Results of this study demonstrate that daily administration of cortisol to 21-day-old suckling pigs for 2 days enhanced intestinal ODC activity (Fig. 2) and polyamine synthesis (Table 3). This is the first report of increases in both ODC activity and polyamine synthesis in enterocytes of cortisol-treated neonatal pigs. In these cells, induction of both arginase (14) and ODC (Fig. 2) results in polyamine synthesis from arginine, whereas increased ODC activity (Fig. 2) accounts for the enhanced synthesis of polyamines from proline. Spermidine was the major polyamine formed from ornithine in pig enterocytes, followed by putrescine and spermine (Table 3). Interestingly, intracellular concentrations of putrescine were the lowest among all three polyamines measured (Fig. 3). This result may be explained by the contribution of milk-born polyamines to intestinal concentrations in suckling neonates, as spermine is more abundant than spermidine in sow's milk (20) as in human and rat milk (24), and sow's milk contains little putrescine (20). RU-486 administration increased plasma cortisol concentrations in piglets (Fig. 1; see Ref. 15), as reported for humans (5). This result may be explained by the hypersecretion of cortisol from the adrenal cortex (5) and possibly decreased cellular uptake of cortisol. Administration of RU-486 alone had no effect on intestinal ODC or polyamine synthesis (Fig. 2 and Table 3) or intestinal arginine metabolism (14) in suckling pigs, suggesting that basal, endogenous glucocorticoid levels do not play a role in these metabolic pathways. There are circadian variations of plasma cortisol concentrations (6-24 µg/l) in pigs, with the highest and lowest values found at 8:00 AM and 12:00 AM, respectively (30). An important finding of this study is that coadministration of RU-486 abolished the stimulating effect of exogenous cortisol on intestinal ODC activity and polyamine synthesis in neonatal pigs, regardless of plasma cortisol concentrations (Fig. 2). These results indicate that an increase in plasma cortisol concentrations enhances enterocyte ODC activity and polyamine synthesis via a glucocorticoid receptor-mediated mechanism, as we previously reported for the induction of intestinal arginase in suckling pigs (14).
Role of amino acids in intestinal polyamine synthesis.
Glucocorticoid treatment decreases intestinal lactase activity and
increases intestinal sucrase and maltase activities in suckling rats
and pigs (8, 16). In addition, cortisol
administration increases arginine and glutamine metabolism in pig
enterocytes (14). Our current study extends the regulatory
role of glucocorticoids in intestinal digestive enzymes and amino acid
metabolism (13-16) to polyamine synthesis in suckling
pigs. Another important, novel finding of this study is the relative
importance of potential substrates for polyamine synthesis in
enterocytes (Fig. 5). Ornithine is the
immediate precursor for the synthesis of putrescine by ODC. However,
because milk contains only a negligible amount of ornithine
(9, 34) and because there is little uptake of
arterial ornithine by the small intestine (33), it is
important to identify the metabolic sources of ornithine for intestinal
polyamine synthesis in suckling neonates. Although arginine is often
assumed to be the major precursor of ornithine in mammalian cells
(39), this pathway is insignificant for enterocytes of
suckling mammals because of a low or negligible activity of intestinal
arginase (37).
|
Anabolic effect of cortisol on intestinal growth.
Daily intramuscular administration of cortisol (25 mg HYD/kg body wt)
to 21-day-old suckling pigs for 2 days resulted in elevated plasma
concentrations of cortisol at day 2 posttreatment (Fig. 1)
to values similar to those observed in newborn piglets
(27). The daily dose of HYD used in our study is
equivalent to 1 mg dexamethasone · kg body
wt1 · day
1 (1). It is
noteworthy that this cortisol treatment increased intestinal polyamine
synthesis, villus height, and small intestine growth in suckling
piglets (Tables 1 and 3). These beneficial effects of cortisol
administration were not due to an altered supply of dietary nutrients
because milk consumption did not differ between control and
cortisol-treated piglets. Similarly, Chappel et al. (8)
found that a single administration of HYD (25 mg/kg body wt) to
suckling piglets increased small-intestinal growth, reduced postweaning
mortality, and improved growth rate of piglets weaned at 14 days of
age. A cortisol surge during the perinatal period is also associated
with intestinal maturation and growth in piglets (27).
Collectively, these results suggest an anabolic effect of physiological
concentrations of cortisol on the small intestine in neonatal pigs.
Interestingly, Rhoads et al. (26) showed that
glucocorticoid treatment (30 mg methylprednisolone · kg body
wt
1 · day
1 for 2 days) had no effect
on jejunal villus height or crypt depth in healthy piglets weaned at
17-21 days of age but increased jejunal villus height by 120% in
weaned piglets infected with a gastroenteritis virus. In contrast, Wang
and Johnson (29) reported that multiple glucocorticoid
administrations (5 mg corticosterone/kg body wt, 3 times daily for 3 days) to 22-h-fasted young rats caused significant damage to duodenal
mucosa. Burrin et al. (7) also observed that daily
administration of dexamethasone (1 mg/kg body wt) to 2-day-old pigs for
7 days decreased intestinal protein synthesis and mucosal mass. Whether
glucocorticoids promote intestinal anabolism or catabolism likely
depends on the following factors: 1) the type of
corticosteroids administered (e.g., natural or synthetic), 2) the frequency of corticosteroid administration,
3) the concentrations of circulating corticosteroids,
4) the tissue sensitivity to corticosteroids, and
5) the species and developmental stages studied. We suggest that an increase in plasma cortisol concentrations within physiological ranges may be beneficial for stimulating small intestine growth and
development in suckling neonates.
Physiological and nutritional significance. Polyamines are essential for protein synthesis as well as intestinal maturation and function (11, 17, 23). Thus results of this study have important implications for intestinal physiology and nutrition in neonates. First, enhanced intestinal synthesis of polyamines may help explain the beneficial effect of prenatal or postnatal administration of glucocorticoids on improving gut maturation and function (1) as well as decreasing the incidence of necrotizing enterocolitis (2) in premature infants. Our results may also provide a metabolic basis for the more rapid intestinal villus recovery in piglet viral enteritis after treatment with glucocorticoid (26). Second, reduced intestinal synthesis of polyamines may be a biochemical basis for the gut atrophy frequently observed in neonates maintained on glutamine-free parenteral nutrition solutions (10). This is likely due to a limited supply of arterial amino acid substrates for polyamine synthesis in intestinal mucosa. Third, enteral provision of amino acids, including proline, glutamine, glutamate, arginine, and ornithine, may be critical for optimizing intestinal polyamine synthesis and therefore intestinal development and integrity. This may help explain the previous findings that early introduction of enteral feeding promotes intestinal maturation and motility in preterm infants (4).
![]() |
ACKNOWLEDGEMENTS |
---|
We thank Wene Yan, E. Lichar Dillon, Erin Hilbun, Sean Flynn, and Edward Gregg for technical assistance, Tony Haynes for preparing figures, and Frances Mutscher for secretarial support.
![]() |
FOOTNOTES |
---|
This research was supported by United States Department of Agriculture Grant 97-35206-5096 (to G. Wu) and by Hatch Projects H8200 (G. Wu) and H6601 (D. A. Knabe) from the Texas Agricultural Experiment Station.
Address for reprint requests and other correspondence: G. Wu, Dept. of Animal Science, Texas A&M Univ., 2471 TAMUS, College Station, TX 77843-2471 (E-mail: g-wu{at}tamu.edu).
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. §1734 solely to indicate this fact.
Received 4 January 2000; accepted in final form 23 February 2000.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Ballard, PL,
and
Ballard RA.
Scientific basis and therapeutic regimens for use of antenatal glucocorticoids.
Am J Obstet Gynecol
173:
254-262,
1995[ISI][Medline].
2.
Bauer, CR,
Morrison JC,
Poole WK,
Korones SB,
Boehm JJ,
Rigatto H,
and
Zachman RD.
A decreased incidence of necrotizing enterocolitis after prenatal glucocorticoid therapy.
Pediatrics
73:
682-688,
1984[Abstract].
3.
Baulieu, EE.
Contragestion and other clinical applications of RU486, an antiprogesterone at the receptor.
Science
245:
1351-1357,
1989[ISI][Medline].
4.
Berseth, CL,
and
Nordyke C.
Enteral nutrients promote postnatal maturation of intestinal motor activity in preterm infants.
Am J Physiol Gastrointest Liver Physiol
264:
G1046-G1051,
1993
5.
Bertagna, X,
Bertagna C,
Laudat M,
Husson J,
Girard F,
and
Luton J.
Pituitary-adrenal response to the anti-glucocorticoid action of RU486 in Cushing's syndrome.
J Clin Endocrinol Metab
63:
639-643,
1986[Abstract].
6.
Brunton, JA,
Bertolo RFP,
Pencharz PB,
and
Ball RO.
Proline ameliorates arginine deficiency during enteral but not parenteral feeding in neonatal piglets.
Am J Physiol Endocrinol Metab
277:
E223-E231,
1999
7.
Burrin, DG,
Wester TJ,
Davis TA,
Fiorotto ML,
and
Chang X.
Dexamethasone inhibits small intestinal growth via increased protein catabolism in neonatal pigs.
Am J Physiol Endocrinol Metab
276:
E269-E277,
1999
8.
Chappel, R,
Cuaron JP,
and
Easter RA.
Effect of glucocorticoids and limited nursing on the carbohydrate digestive capacity and growth rate of piglets.
J Anim Sci
67:
2956-2973,
1989[ISI][Medline].
9.
Davis, TA,
Nguyen HV,
Garcia-Bravo R,
Florotto ML,
Jackson EM,
Lewis DS,
Lee DR,
and
Reeds PJ.
Amino acid composition in human milk is not unique.
J Nutr
124:
1126-1132,
1994[ISI][Medline].
10.
Dudley, MA,
Wykes LJ,
Dudley AW, Jr,
Burrin DG,
Nichols BL,
Rosengerger J,
Jahoor F,
Heird WC,
and
Reeds PJ.
Parenteral nutrition selectively decreases protein synthesis in the small intestine.
Am J Physiol Gastrointest Liver Physiol
274:
G131-G137,
1998
11.
Dufour, C,
Dandrifosse G,
Forget P,
Vermesse F,
Romain N,
and
Lepoint P.
Spermine and spermidine induce intestinal maturation in the rat.
Gastroenterology
95:
112-116,
1988[ISI][Medline].
12.
Fell, D.
Understanding the Control of Metabolism. London: Portland, 1997, p. 301.
13.
Flynn, NE,
Meininger CJ,
Kelly K,
Ing NH,
Morris SM, Jr,
and
Wu G.
Glucocorticoids mediate the enhanced expression of intestinal type II arginase and argininosuccinate synthase in postweaning pigs.
J Nutr
129:
799-803,
1999
14.
Flynn, NE,
and
Wu G.
Enhanced metabolism of arginine and glutamine in enterocytes of cortisol-treated pigs.
Am J Physiol Gastrointest Liver Physiol
272:
G474-G480,
1997
15.
Flynn, NE,
and
Wu G.
Glucocorticoids play an important role in mediating the enhanced metabolism of arginine and glutamine in enterocytes of postweaning pigs.
J Nutr
127:
732-737,
1997
16.
Henning, SJ.
Postnatal development: coordination of feeding, digestion, and metabolism.
Am J Physiol Gastrointest Liver Physiol
241:
G199-G214,
1981
17.
Johnson, LR.
Regulation of gastrointestinal mucosal growth.
Physiol Rev
68:
456-502,
1988
18.
Kandil, HM,
Argenzio RA,
Chen W,
Berschneider HM,
Stiles AD,
Westwick JK,
Rippe RA,
Brenner DA,
and
Rhoads JM.
L-Glutamine and L-asparagine stimulates ODC activity and proliferation in a porcine jejunal enterocyte line.
Am J Physiol Gastrointest Liver Physiol
269:
G591-G599,
1995
19.
Lin, C-H,
Correia L,
Tolia K,
Gesell MS,
Tolia V,
Lee P-C,
and
Luk GD.
Early weaning induces jejunal ornithine decarboxylase and cell proliferation in neonatal rats.
J Nutr
128:
1636-1642,
1998
20.
Motyl, T,
Ploszaj T,
Wojtasik A,
Kukulska W,
and
Podgurniak M.
Polyamines in cow's and sow's milk.
Comp Biochem. Physiol.
111B:
427-433,
1995[ISI].
21.
Noblet, J,
and
Etienne M.
Estimation of sow milk nutrient output.
J Anim Sci
67:
3352-3359,
1989[ISI][Medline].
22.
Nsi-Emvo, E,
Chaton B,
Foltzer-Jourdainne C,
Gosse F,
and
Raul F.
Premature expression of sucrase-isomaltase triggered by corticoid-dependent changes in polyamine metabolism.
Am J Physiol Gastrointest Liver Physiol
270:
G54-G59,
1996
23.
Pegg, AE.
Recent advances in the biochemistry of polyamines in eukaryotes.
Biochem J
234:
249-262,
1986[ISI][Medline].
24.
Pollack, PF,
Koldovsky O,
and
Nishioka K.
Polyamines in human and rat milk and in infant formulas.
Am J Clin Nutr
56:
371-375,
1992[Abstract].
25.
Reeds, PJ,
Burrin DG,
Stoll B,
Jahoor F,
Wykes L,
Henry J,
and
Frazer ME.
Enteral glutamate is the preferential source for mucosal glutathione synthesis in fed piglets.
Am J Physiol Endocrinol Metab
273:
E408-E415,
1997
26.
Rhoads, JM,
Macleod RJ,
and
Hamilton JR.
Effect of glucocorticoid on piglet jejunal mucosa during acute viral enteritis.
Pediatr Res
23:
279-282,
1988[Abstract].
27.
Sangild, PT,
Sjostrom H,
Noren O,
Fowden AL,
and
Silver M.
The prenatal development and glucocorticoid control of brush-border hydrolases in the pig small intestine.
Pediatr Res
37:
207-212,
1995[Abstract].
28.
Steel, RGD,
and
Torrie JH.
Principles and Procedures of Statistics. New York, NY: McGraw Hill, 1980.
29.
Wang, J-Y,
and
Johnson LR.
Gastric and duodenal mucosal ornithine decarboxylase and damage after corticosterone.
Am J Physiol Gastrointest Liver Physiol
258:
G49-G57,
1990.
30.
Whipp, SC,
Wood RL,
and
Lyon NC.
Diurnal variation in concentrations of hydrocortisone in plasma of swine.
Am J Vet Res
31:
2105-2107,
1970[ISI][Medline].
31.
Worsae, H,
and
Schmidt M.
Plasma cortisol and behaviour in early weaned piglets.
Acta Vet Scand
21:
640-657,
1980[ISI][Medline].
32.
Wu, G.
Synthesis of citrulline and arginine from proline in enterocytes of postnatal pigs.
Am J Physiol Gastrointest Liver Physiol
272:
G1382-G1390,
1997
33.
Wu, G.
Intestinal mucosal amino acid catabolism.
J Nutr
128:
1249-1252,
1998
34.
Wu, G,
and
Knabe DA.
Free and protein-bound amino acids in sow's colostrum and milk.
J Nutr
124:
415-424,
1994[ISI][Medline].
35.
Wu, G,
and
Knabe DA.
Arginine synthesis in enterocytes of neonatal pigs.
Am J Physiol Regulatory Integrative Comp Physiol
269:
R621-R629,
1995
36.
Wu, G,
Knabe DA,
and
Flynn NE.
Synthesis of citrulline from glutamine in pig enterocytes.
Biochem J
299:
115-121,
1994[ISI][Medline].
37.
Wu, G,
Knabe DA,
Flynn NE,
Yan W,
and
Flynn SP.
Arginine degradation in developing porcine enterocytes.
Am J Physiol Gastrointest Liver Physiol
271:
G913-G919,
1996
38.
Wu, G,
Meier SA,
and
Knabe DA.
Dietary glutamine supplementation prevents jejunal atrophy in weaned pigs.
J Nutr
126:
2578-2584,
1996[ISI][Medline].
39.
Wu, G,
and
Morris SM, Jr.
Arginine metabolism: nitric oxide and beyond.
Biochem J
336:
1-17,
1998[ISI][Medline].
40.
Wu, G,
Pond WG,
Flynn SP,
Ott TL,
and
Bazer FW.
Maternal dietary protein deficiency decreases nitric oxide synthase and ornithine decarboxylase activities in placenta and endometrium of pigs during early gestation.
J Nutr
128:
2395-2402,
1998