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Department of Animal Science, North Carolina State University, Raleigh, NC 27695-7621
2To whom correspondence should be addressed. E-mail: jack_odle{at}ncsu.edu
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ABSTRACT |
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 TOP ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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KEY WORDS: • canine • carnitine • carnitine palmitoyltransferase • fatty acid oxidation • ontogeny
Long-chain fatty acid metabolism is tightly linked to the emergence of the carnitine palmitoyltransferase (CPT) system (2 ), in which three distinct enzymes have been identified: mitochondrial outer membrane CPT (CPT I), inner membrane CPT (CPT II) and carnitine-acylcarnitine translocase. Among these, CPT I catalyzes the rate-limiting step of long-chain acyl-CoA translocation into mitochondria for subsequent ß-oxidation (1 ). Studies with food-deprived and diabetic adult animals (2 ,3 ) have shown that long-chain fatty acid oxidation is mainly controlled by changes in CPT I activity, malonyl-CoA concentration (a potent physiological inhibitor of CPT I) and/or the sensitivity of CPT-I to malonyl-CoA inhibition. This regulatory role of CPT I in long-chain fatty acid oxidation is observed not only in different physiological or pathological states but also in different stages of growth and development. It has been reported in rats (4 ,5 ), rabbits (6 ,7 ) and pigs (8 ,9 ) that CPT I activity was very low at birth but increased about 2-fold within 24 h of birth. These dramatic changes during the 1st d of life were paralleled by an increase in fatty acid oxidation. Therefore, the CPT system, especially CPT I, plays a very important role in controlling the rate of fatty acid oxidation in mitochondria.
In addition to mitochondria, CPT activity also is present in other subcellular locations such as peroxisomes and microsomes. The CPT in these subcellular compartments, as well as mitochondrial CPT, share a number of common kinetic and regulatory properties. Both malonyl-CoA–sensitive and –insensitive CPT (mitochondrial CPT I and CPT II, respectively) have been identified and characterized (10 ,11 ). Although the precise physiological role of the CPT system in the extramitochondrial compartments remains to be elucidated, it is clear that the enzymes work coordinately with mitochondrial CPT in fatty acid metabolism (12 ,13 ). The roles of these enzymes in lipid metabolism recently have been stressed and investigated extensively at the subcellular level [see McGarry and Brown (1 ) for review]. However, CPT as a whole—its activity and kinetic constants and their relationship with prevailing tissue carnitine concentrations during development—has not been carefully evaluated, especially in companion animal species.
L-Carnitine is an essential cofactor for the CPT enzyme system. Studies with mitochondria have shown that increasing the carnitine concentration in the mitochondrial matrix increases CPT activity, stimulates translocase activity and increases the flux of fatty acids through mitochondrial ß-oxidation (14 ). As one of the substrates of CPT, carnitine’s availability is very important for optimal CPT activity and fatty acid oxidation. Carnitine also participates in a variety of other metabolic events, such as branched-chain amino acid metabolism, ketogenesis, lipolysis and de novo synthesis of fatty acids (15 ). All of these functions may vary with postnatal development and are especially important for the viability of newborns. Neonates cannot synthesize adequate amounts of carnitine de novo because of a low activity of butyrobetaine hydrolase, and therefore carnitine status declines if exogenous carnitine is not supplied. On this basis, supplementation of carnitine to human neonates has been strongly advocated (16 ). Beneficial effects of adding carnitine to the diet also have been observed recently in growing farm animals (17 –20 ). Depending on animal species, age and tissue, carnitine concentrations vary widely (15 ). The plasma carnitine level is commonly used to estimate carnitine status, but it does not necessarily reflect tissue carnitine levels (21 ). Thus, carnitine content in tissue is an important index to evaluate carnitine status, especially during early development (21 ).
In the present study, CPT activity and carnitine concentrations were examined in liver and skeletal muscle homogenates during postnatal development of dogs. The examination was specifically focused on changes in CPT activity and carnitine concentrations at birth, suckling and before and after weaning. The relationships between enzyme activity and carnitine requirement (evaluated by the carnitine Km) and carnitine concentrations in the tissues are presented and discussed.
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MATERIALS AND METHODS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Timed-pregnant Beagle bitches (n = 15) were housed in standard dog runs designed to satisfy PHS and AAALAC housing criteria. Details of dog feeding and management are reported elsewhere (22 ). Briefly, the bitches were given free access to commercially available complete food (Eukanuba Premium Performance, The Iams Co., Dayton, OH) that exceeded NRC 1985 nutrient recommendations (23 ). After whelping, puppies remained with their mothers and were allowed to suckle until 6 wk of age. At 2 wk before weaning (4 wk of age), puppies were given access to mash feed consisting of a finely ground commercial puppy food (Eukanuba Puppy Small Bite, The Iams Co.) mixed with water. After 6 wk, the puppies were fed only the dry puppy food that again was formulated to exceed established nutrient requirements (22 ). Carnitine concentrations in both adult and puppy diets ranged from 15 to 30 mg/kg. At designated ages, dogs were killed after consuming the morning meal as previously described (22 ) and tissues (liver and skeletal muscle) from the newborn; 24-h-old (suckled); 3-, 6- and 9-wk-old; and adult dogs were sampled and then frozen immediately in liquid nitrogen. The samples were stored at -80°C until analysis.
CPT activity analysis.
Frozen tissues were homogenized with 4 volumes of a medium containing 220 mmol/L mannitol, 70 mmol/L sucrose, 2 mmol/L HEPES and 0.1 mmol/L EDTA (pH = 7.2 at 4°C) using a hand-driven ground-glass homogenizer. After homogenization, CPT activity in the whole tissue homogenate was analyzed over a range of carnitine concentrations (0–2.5 mmol/L) at 30°C, with a modification of the procedure described by Bremer et al. (24
). The reaction medium contained in a total volume of 1.0 mL, 75 mmol/L KCl, 50 mmol/L mannitol, 25 mmol/L HEPES, 0.2 mmol/L EGTA, 2.0 mmol/L KCN, 10 g/L essential fatty acid (EFA)–free BSA, 1 mmol/L dithiothreitol and 80 µmol/L palmitoyl-CoA. The medium was preincubated with 50 µL of homogenate (2–3.5 mg of protein) for 3 min, then the reaction was started by adding L-[N-methyl-H3]carnitine (1.67 MBq/µmol) and was terminated by addition of 2 mL of 60 g/L HClO4 after 6 min of incubation. The labeled palmitoyl carnitine generated from the reaction was extracted by use of water-saturated butanol, and radioactivity was determined by liquid scintillation spectrometry (LS-6500 IC; Beckman Instruments, Fullerton, CA). The specific radioactivity was kept constant for each carnitine concentration used in the assays and results were blank-corrected by use of a standard curve obtained from samples terminated at 0-min incubation for each concentration of carnitine. Tissue contents of the homogenate were determined by weight (
20 g/100 g), and homogenate protein was analyzed by use of the Biuret method (25
). Enzyme activity was expressed per g of wet tissue.
Carnitine analysis.
Free carnitine (FC) and carnitine esters in tissues were measured by the enzymatic radioisotope method of McGarry and Foster (26 ), with a modification as described by Bhuiyan et al. (27 ). Frozen tissues (0.5 g) were homogenized in ice-cold HClO4 (1 mol/L) by use of a PowGen polytron (Fisher Scientific, Pittsburgh, PA). The homogenate was centrifuged at 10,000 x g for 5 min and the supernatant was reserved in a 2-mL centrifuge tube. The pellet was washed with ice-cold HClO4 (0.1 mol/L) and recentrifuged. The supernatants from the two extractions were combined and neutralized with KOH (1 mol/L). After neutralization, the resultant precipitate was removed by centrifugation and the supernatant was divided into two parts. One part was used for FC analysis directly, and the other was used for short-chain acylcarnitine (SC) analysis after alkaline hydrolysis with KOH at 60°C for 60 min. Long-chain acylcarnitines (LC) were analyzed after alkaline hydrolysis of the tissue pellet under the same alkaline conditions as for the SC. All samples were prepared and analyzed in duplicate. Analyses were conducted in HEPES–EDTA buffer (pH = 7.3) with 25.5 nmol [1-14C]acetyl-CoA (37 kBq/µmol), 2 µmol N-ethymaleimide and 1 IU carnitine acetyltransferase at 25°C for 30 min. Acetyl-carnitine was separated on a column packed with resin (AG 1x8, 100–200, chloride form; Bio-Rad, Richmond, CA), and the radioactivity in the column effluent was measured by liquid scintillation.
Chemicals.
(L)-[N-Methyl-3H]carnitine hydrochloride (2.5 GBq/mol) and [1-14C]acetyl-CoA (148 MBq/mmol) were purchased from American Radiolabeled Chemicals (St. Louis, MO). L-Carnitine (inner salt) was a gift from Lonza AG (4002; Basel, Switzerland). Carnitine acetyltransferase (EC 2.3.1.7), palmitoyl-CoA, acetyl-CoA and other chemicals were obtained from Sigma Chemicals (St. Louis, MO).
Statistics.
According to the Michaelis–Menten equation, Vi = Vmax[s]/(Km + [s]), the apparent kinetic constants of CPT (Vmax and Km for carnitine) were calculated by use of the iterative NLIN procedure of SAS (28 ). The computed apparent Vmax is referred to as maximal activity throughout the manuscript. The calculated data (the enzyme kinetic constants) and all other analytical data were analyzed by one-way ANOVA appropriate for a completely random design by use of the GLM procedure of SAS (28 ), and means were separated by use of a protected LSD test (28 ). Differences were considered significant at P < 0.05.
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RESULTS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Hepatic CPT activity (Fig. 1 ) increased with age from birth to 6 wk of age and then declined. Activity in adults was similar to that in 24-h-old dogs, whereas maximal activity in newborns was lower (P < 0.02). The asymptotic maximal activities of CPT (i.e., from extrapolated curves) were 56% greater in 24-h-old and 3-, 6- and 9-wk-old dogs than in newborn and adult dogs (P < 0.01, Table 1 ). The apparent carnitine Km tended to increase from birth to 3 wk of age and then decreased and remained constant after 6 wk of age (Table 2 ). The highest apparent Km (0.84 mmol/L) was in 3-wk-old dogs and was about 50% greater than in the older dogs (P < 0.05).
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Carnitine concentrations.
Concentrations of free carnitine (FC) and LC carnitine esters in liver decreased rapidly with age from birth to 3 wk (Table 3 ). After 3 wk of age, SC decreased, whereas FC and LC remained relatively constant. Free carnitine and total carnitine (TC) were about 100% higher in neonatal dogs than in all other age groups (P < 0.05). SC concentrations in young dogs (from newborn to 3 wk) were 2.8-fold those in older dogs (6 and 9 wk of age), and nearly 10-fold the concentrations in adult dogs (P < 0.05).
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These variables did not differ between genders within age groups for either liver or muscle tissue (data not shown).
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DISCUSSION |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Effect of age on carnitine palmitoyltransferase activity.
Fatty acid concentration in plasma increases dramatically after birth because of the mobilization of endogenous triglycerides and the hydrolysis of exogenous triglycerides from milk (32 ). To meet the energy needs of newborns, fatty acid oxidation must develop rapidly after birth in the liver and in extrahepatic tissues (32 ). Indeed, studies with rats have shown that fatty acid oxidation by isolated hepatocytes increased by 6- to 10-fold during the neonatal period (33 ). Moreover, the increase in fatty acid oxidation is paralleled by the development of the mitochondrial CPT enzymatic system. It was reported that hepatic mitochondrial CPT I activity increased 2- to 6-fold in the first 24 h, reaching the same level as that in adults rats (5 ,34 ), rabbits (6 ) and pigs (9 ). The CPT activity measured in canine liver tissue homogenates agrees with these earlier reports. Activity was 60% greater in 24-h-old dogs compared to newborn dogs and showed no further increase, suggesting that the capacity for fatty acid oxidation is activated effectively in dogs within the first 24 h after birth. After 24 h, hepatic activity remained elevated throughout the suckling period. Activity began decreasing after 6 wk, at which time the puppies were fully weaned onto solid food. Lonnerdal et al. (35 ) reported that the energy content of dog milk increased during the first 40 d of lactation and decreased during d 41–50, corresponding to changes in fat content (36 ). Therefore, changes in CPT activity during suckling and at weaning may be effected by changes in dietary fat. Such correspondence has been reported in research with rats (37 ,38 ). Although hepatic CPT activity (per g wet weight) fell after 6–9 wk of age, total hepatic activity (expressed on a whole-liver basis) continued to increase as a result of increasing liver weight (Fig. 3 ). Expressed on a body-weight basis, hepatic activity was unchanged throughout development; thus, capacity increased proportionally to body weight.
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Changes in tissue carnitine concentration with age.
Hepatic carnitine concentrations in the developing dogs were consistent with those in developing rats (43 ). Concentrations gradually decreased with age and reached adult concentrations by weaning age. Concentrations were maximal at birth, suggesting that a reasonable capacity for placental carnitine transfer may exist. Indeed, carnitine concentrations in fetal tissues depend on both maternal carnitine levels (44 ) and placental transfer rate (45 ). Suckling in the first 24 h did not increase hepatic carnitine. However, the changes in concentrations during the suckling period may well reflect changes in carnitine concentration of dog milk because milk is the only source of exogenous carnitine during this time and carnitine synthesis in neonates is very low because of a minimum activity of butyrobetaine hydroxylase (46 ,47 ). In addition, the ratio of acylcarnitine/carnitine in neonatal and younger dogs was 2–4.5 times that of adult dogs.
A similar profile was observed in serum from developing rats (48 ). Several explanations for the high acylcarnitine concentration in neonatal dogs are possible. First, the acylcarnitine may have originated from dog milk, given that it was reported that early human milk contains a higher ratio of acylcarnitine/carnitine than does mature milk (41 ). Second, the high acylcarnitine level correlates with a high milk lipid content and accelerated fatty acid oxidative capacity during the suckling period. Indeed, serum acylcarnitine concentration in rats is associated with dietary lipid content (49 ). When rats were weaned and the lipid contribution from milk was lost, the acylcarnitine concentration decreased as well. Corsi (50 ) suggested that the ratio of acylcarnitine to free carnitine was about 0.2 under normal conditions, but it could be affected by the composition of diet and availability of glucose (51 ). Third, acetate plays an important role in liver fatty acid metabolism of the canine, and we suggest that a high propensity to activate short-chain fatty acids (SCFA) for entry into metabolism (52 ) may result in the large proportion of acid-soluble carnitine.
The carnitine concentrations in muscle at birth and during suckling were similar to those in liver, but generally increased after 3 wk of age. Concentrations were extremely low in neonatal and young dogs compared to adults. Tissue carnitine must be provided via plasma, where it originates from the diet or from carnitine synthesis in the liver, as it cannot be synthesized in cardiac or skeletal muscle (15 ). Thus, the tissue concentration depends on the dietary carnitine level, the rate of hepatic carnitine de novo synthesis, and the rate of carnitine uptake by the tissue. During suckling, when carnitine synthesis is low (46 ), carnitine in the milk seems to be the primary source. Thus, the decrease in muscle carnitine during the first 3 wk may be associated with declining milk carnitine content. After 3 wk, the concentration in muscle gradually increased. This increase could have been caused by the presence of more carnitine in the solid food compared to the milk from late lactation, but this is speculative because we did not measure milk carnitine concentrations. It also could be caused by an increase in carnitine uptake capacity of the tissue and/or by an increase in carnitine synthesis. It appeared that carnitine accumulation in muscle formed the largest reserve in the body. This was consistent with the report that in adult dogs, carnitine in cardiac and skeletal muscle constitutes 95–98% of the body pool (53 ).
Relationship between apparent carnitine Km and tissue carnitine concentration.
Carnitine, as a substrate for CPT, plays a very important role in activating and controlling the carnitine-dependent fatty acid transport system. However, the carnitine concentration required for optimal CPT activity and fatty acid oxidation is unknown. Long et al. (54 ) in 1982 tested the relationship between carnitine and oleate oxidation in homogenates prepared from liver, heart, skeletal muscle and kidney of rats, and from canine and human skeletal muscle. He found that the carnitine requirement for long-chain fatty acid oxidation varied markedly, but was roughly proportional to the concentration of carnitine normally present in the tissue. However, the relationship between the carnitine requirement for CPT activity and tissue carnitine concentrations was not evaluated in their study. Apparent carnitine Km, as one of the enzyme kinetic constants, could be a very useful index for evaluation of carnitine status in the tissue. In fact, many enzymes possess Km values that approximate the physiologic concentration of their substrate such that variation in substrate concentration will proportionally affect the rate of enzyme activity. Our study showed that the apparent carnitine Km in liver increased from birth to 3 wk of age, consistent with the postnatal increase in fatty acid oxidative capacity.
To ensure that fatty acid metabolism is favored toward oxidation, increased CPT activity is often accompanied by a reduced sensitivity to malonyl-CoA inhibition and a rise in carnitine Km because these parameters are inversely related (55 ,56 ). However, the carnitine concentrations decreased with age during the first 3 wk (Fig. 4 ). In the first 24 h after birth, carnitine concentrations in liver were 50% higher than the apparent carnitine Km of CPT and apparently meet the requirement of carnitine for a half-maximum velocity of CPT. This may be important for the newborn to aid in adaptation from the use of fetal carbohydrate fuel to the use of milk fat postnatally as a primary fuel. After 24 h, carnitine concentrations continued to decrease and at 3 wk of age, the apparent carnitine Km was significantly higher than the carnitine concentration in the tissue, suggesting that the initial velocity of CPT may be limited by the available carnitine. However, whether the potential limitation in velocity of CPT observed in the tissue from 3-wk-old dogs would result in a limitation in fatty acid oxidation in vivo is unknown. With respect to enzyme kinetics, the enzyme velocity depends on substrate concentration, especially when the substrate concentration is low; thus, supplementation of carnitine could be of benefit for the animal at this age. After 3 wk of age, the apparent carnitine Km decreased and remained similar in magnitude to the tissue carnitine concentration. This demonstrated that CPT, as a key enzyme, is affected by the substrate carnitine concentration, and suggests that carnitine, at least in liver, may play a regulatory role in fatty acid metabolism in vivo.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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3 Abbreviations used: CPT, carnitine palmitoyltransferase; FC, free carnitine; LC, long-chain carnitine esters; SC, short-chain carnitine esters; TC, total carnitine.
Manuscript received 12 October 2002. Initial review completed 4 November 2002. Revision accepted 28 December 2002.
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LITERATURE CITED |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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1. McGarry, J. D. & Brown, N. F. (1997) The mitochondrial carnitine palmitoyltransferase system. From concept to molecular analysis. Eur. J. Biochem. 244:1-14.[Medline]
2. McGarry, J. D. & Foster, D. W. (1980) Regulation of hepatic fatty acid oxidation and ketone body production. Annu. Rev. Biochem. 49:395-420.[Medline]
3. Cook, G. A., Stephens, T. W. & Harris, R. A. (1984) Altered sensitivity of carnitine palmitoyltransferase to inhibition by malonyl-CoA in ketotic diabetic rats. Biochem. J. 219:337-339.[Medline]
4. Girard, J., Duee, P. H., Ferr, P., Pegorier, J. P., Escriva, F. & Decaux, J. F. (1985) Fatty acid oxidation and ketogenesis during development. Reprod. Nutr. Dev. 25:303-319.
5. Penas, M. & Benito, M. (1986) Regulation of carnitine palmitoyltransferase activity in the liver and brown adipose tissue in the newborn rat: effect of starvation and hypothermia. Biochem. Biophys. Res. Commun. 136:589-596.
6. Herbin, C., Pegorier, J. P., Duee, P. H, Kohl, C. & Girard, J. (1987) Regulation of fatty acid oxidation in isolated hepatocytes and liver mitochondria from newborn rabbits. Eur. J. Biochem. 165:201-207.[Medline]
7. Pegorier, J. P., Garcia-Garcia, M. V., Prip-Buus, C., Duee, P. H., Kohl, C. & Girard, J. (1989) Induction of ketogenesis and fatty acid oxidation by glucagon and cyclic AMP in cultured hepatocytes from rabbit fetuses. Biochem. J. 264:93-100.[Medline]
8. Bieber, L. L., Markwell, M.A.K., Blair, M. & Helmrath, T. A. (1973) Studies on the development of carnitine palmitoyltransferase and fatty acid oxidation in liver mitochondria of neonatal pigs. Biochim. Biophys. Acta 326:145-154.[Medline]
9. Lin, X. & Odle, J. (1995) Regulation of fatty acid oxidation by hepatic mitochondria from neonatal pigs via carnitine palmitoyltransferase I. J. Anim. Sci. 73(suppl. 1):77.[Abstract]
10. Murthy, S. R. & Pande, S. V. (1994) Malonyl-CoA–sensitive and –insensitive carnitine palmitoyltransferase activities of microsomes are due to different proteins. J. Biol. Chem. 269:18283-18286.
11. Singh, H., Beckman, K. & Poulos, A. (1996) Evidence of two catalytical active carnitine medium/long chain acyltransferases in rat liver peroxisomes. J. Lipid Res. 37:2616-2626.[Abstract]
12. Ramsay, R. R. (1994) Carnitine and its role in acyl group metabolism. Essays Biochem. 28:47-61.[Medline]
13. Broadway, N. M. & Saggerson, E. D. (1995) Microsomal carnitine acyltransferases. Biochem. Soc. Trans. 23:490-494.[Medline]
14. Pande, S. V. & Parvin, R. (1980) Carnitine-acylcarnitine translocase-mediated transport of fatty acids into mitochondria: its invovment in the control of fatty acid oxidation in liver. Frenkel, R. A. McGarry, J. D. eds. Carnitine Biosynthesis, Metabolism, and Functions 61:43-157 .
15. Bremer, J. (1983) Carnitine—metabolism and functions. Physiol. Rev. 63:420-480.
16. Schmidt-Sommerfeld, E. & Penn, D. (1990) Carnitine and total paraenteral nutrition of the neonate. Biol. Neonate 58(supp1. 1):81-88.
17. Owen, K. Q., Nelssen, J. L., Goodband, M. D., Weeden, T. L. & Blum, S. A. (1996) Effect of L-carnitine and soybean oil on growth performance and body composition of early-weaned pigs. J. Anim. Sci. 74:1612-1619.[Abstract]
18. Heo, K., Odle, J., Han, I. K., Cho, W., Seo, S., VanHeugten, E. & Pilkington, D. H. (2000) Dietary L-carnitine improves nitrogen utilization in growing pigs fed low energy, fat-containing diets. J. Nutr. 130:1809-1814.
19. Heo, K., Odle, J. & Han, I. K. (2000) Effects of dietary L-carnitine and protein level on plasma carnitine, energy and carnitine balance, and carnitine biosynthesis of 20 kg pigs. Asian-Aust. J. Anim. Sci. 13:1568-1575.
20. Heo, K., Lin, X., Odle, J. & Han, I. K. (2000) Kinetics of carnitine palmitolytransferase I are altered by dietary variables and suggest a metabolic need for supplemental carnitine in young pigs. J. Nutr. 130:2467-2470.
21. Atkins, J. & Clandinin, M. T. (1990) Nutritional significance of factors affecting carnitine dependent transport of fatty acid in neonates: a review. Nutr. Res. 10:117-128.
22. Paulsen, D. B., Buddington, K. K. & Buddington, R. K. (2003) Dimensions and histology of the canine small intestine during postnatal development. Am. J. Vet. Res. (in press).
23. National Research Council (NRC) (1985) Nutrient Requirements of Dogs. National Academy of Sciences, Washington, DC. 1985 Academic Press Inc. New York.
24. Bremer, J., Woldegiorgis, G., Schalinske, K. & Shrago, E. (1985) Carnitine palmitoyltransferase activation by palmitoyl-CoA and inactivation by malonyl-CoA. Biochem. Biophys. Acta 833:9-16.[Medline]
25. Layne, E. (1957) Spectrophotometric methods for measuring proteins. Colowick, S. P. Kaplan, N. D. eds. Methods in Enzymology III:447 Academic Press Inc. New York. .
26. McGarry, D. J. & Foster, D. W. (1976) An improved and simplified radioisotopic assay for the determination of free and esterified carnitine. J. Lipid Res. 17:277-281.[Abstract]
27. Bhuiyan, A.K.M.J., Jackson, S., Turnbull, D. M., Aynsley-Green, A., Leonard, J. V. & Bartlett, K. (1992) The measurement of carnitine and acyl-carniitnes: application to investigation of patients with suspected inherited disorders of mitochondrial fatty acid oxidation. Clin. Chim. Acta 207:185-204.[Medline]
28. SAS Institute, Inc. (1989) 4th ed. SAS/STAT User’s Guide, Version 6 2 SAS Institute Cary, NC.
29. Sanderson, S. L., Gross, K. L., Ogburn, P. N., Calvert, C., Jacobs, G., Lowry, S. R., Bird, K. A., Koehler, L. A. & Swanson, L. L. (2001) Effects of dietary fat and L-carnitine on plasma and whole blood taurine concentrations and cardiac function in healthy dogs fed protein-restricted diets. Am. J. Vet. Res. 62:1616-1623.[Medline]
30. Costa, N. D. & Labuc, R. H. (1994) Case report: efficacy of oral carnitine therapy for dilated cardiomyopathy in boxer dogs. J. Nutr. 124:2687S-2692S.
31. Kobayashi, A. & Fujisawa, S. (1994) Effect of L-carnitine on mitochondrial acyl CoA esters in the ischemic dog heart. J. Mol. Cell Cardiol. 26:499-508.[Medline]
32. Girard, J., Ferre, P., Pegorier, J. P. & Duee, P. H. (1992) Adaptations of glucose and fatty acid metabolism during perinatal period and suckling-weaning transition. Physiol. Rev. 72:507-562.
33. Ferr, P., Satabin, P., Decaux, J. F., Escriva, F. & Girard, J. (1983) Development and regulation of ketogenesis in hepatocytes isolated from newborn rats. Biochem. J. 214:937-942.[Medline]
34. Augenfeld, J. & Fritz, B. (1970) Carnitine palmitoyltransferase activity and fatty acid oxidation by livers from fetal and neonatal rats. Can. J. Biochem. 48:288-294.[Medline]
35. Lönnerdal, B., Keen, C. L., Hurley, L. S. & Fisher, G. L. (1981) Developmental changes in the composition of beagle dog milk. Am. J. Vet. Res. 42:662-666.[Medline]
36. Lönnerdal, B. (1996) Lactation in the dog and cat. Carey, D. P. Norton, S. A. Bolser, S. M. eds. Recent Advances in Canine and Feline Nutritional Research, 1996 Iams International Nutrition Syposium Proceedings I Orange Frazer Press Wilmington, OH. .
37. Thumklin, S., Esser, V., Charvy, D., Kolodziej, M., Zammit, V. A., McGarry, D., Girard, J. & Pegorier, J. P. (1994) Expression of liver carnitine palmitoyltransferase I and II genes during development in the rat. Biochem. J. 300:583-587.
38. Decaux, J. F., Ferre, P., Robin, D., Robin, P. & Girard, J. (1988) Decreased hepatic fatty acid oxidation at weaning in the rat is not linked to a variation of malonyl-CoA concentration. J. Biol. Chem. 263:3284-3289.
39. Veerkamp, J. H. & Van Moerkerk, H.T.B. (1982) The effect of malonyl CoA on fatty acid oxidation in rat muscle and liver mitochondria. Biochem. Biophys. Acta 710:252-255.[Medline]
40. Mynatt, R. L., Lappi, M. D. & Cook, G. A. (1992) Myocardial carnitine palmitoyltransferase of the mitochondrial outer membrane is not altered by fasting. Biochem. Biophys. Acta 1128:105-111.[Medline]
41. Power, G. W. & Newsholme, E. A. (1997) Dietary fatty acids influence the activity and sensitivity of mitochondrial carnitine palmitoyltransferase I to inhibition by malonyl CoA in rat heart and skeletal muscle. J. Nutr. 127:2142-2150.
42. Lepine, A. (1998) Nutritional management of the large breed puppy. Reinhart, G. A. Carey, D. C. eds. Recent Advances in Canine and Feline Nutrition, 1998 Iams International Nutrition Syposium Proceedings II Orange Frazer Press Wilmington, OH. .
43. Robles-Valdes, C., McGarry, J. D. & Foster, D. W. (1976) Maternal-fetal carnitine relationship and neonatal ketosis in the rat. J. Biol. Chem. 251:6007-6012.
44. Penn, D., Schmidt-Sommerfeld, E. & Pascu, F. (1981) Decreased tissue carnitine concentrations in newborn infants receiving total parenteral nutrition. J. Pediatr. 98:976-978.[Medline]
45. Schmidt-Sommerfeld, E., Penn, D. & Wolf, H. (1981) The influence of maternal fat metabolism on fetal carnitine levels. Early Hum. Dev. 5:232-242.
46. Bargen-Lockner, C., Hahn, P. & Wittmann, B. (1981) Plasma carnitine in pregnancy. Am. J. Obstet. Gynecol. 140:412-414.[Medline]
47. Takahashi, M. & Sawaguchi, S. (1983) Lipid metabolism in parenterally alimented neonates: carnitine blood concentrations and fat utilization. Indian J. Pediatr. 50:161-168.[Medline]
48. Seccombe, D. W., Hahn, P. & Novak, M. (1978) The effect of diet and development on blood levels of free and esterified carnitine in the rat. Biochem. Biophys. Acta 528:483-489.[Medline]
49. Christianson, R. Z. & Bremer, J. (1976) Active transport of butyrobetaine and carnitine into isolated liver cells. Biochim. Biophys. Acta 448:562-577.[Medline]
50. Corsi, M. (1986) Secondary carnitine deficiency. Borum, P. R. eds. Clinical Aspect of Human Carnitine Deficiency 1986:185-203 Pergamon Press New York, NY. .
51. Foster, C.V.L. & Harris, R. C. (1987) Formation of acetylcarnitine in muscle of horse during high intensity exercise. Eur. J. Appl. Physiol. 56:639-642.
52. Baldner, G. L., Flatt, R. E., Shaw, R. N. & Beitz, D. C. (1985) Fatty acid biosynthesis in liver and adipose tissue from dogs. Comp. Biochem. Physiol. B Biochem. Mol. Biol. 82B:153-156.
53. Rebouche, C. J. & Engel, A. G. (1983) Kinetic compartmental analysis of carnitine metabolism in the dog. Arch. Biochem. Biophys. 220:60-70.[Medline]
54. Long, C. S., Haller, R. G., Foster, D. W. & McGarry, J. D. (1982) Kinetics of carnitine-dependent fatty acid oxidation: implications for human carnitine deficiency. Neurology 32:663-666.
55. Rodwell, V. W. (1993) Enzymes: kinetics. Murray, R. K. Granner, D. K. Mayes, P. A. Rodwell, V. W. eds. Harper’s Biochemistry 1993:71-85 Appleton & Lange Norwalk, CT. .
56. McGarry, J. D., Mills, S. E., Long, C. S. & Foster, D. W. (1983) Observations on the affinity for carnitine, and malonyl-CoA sensitivity, of carnitine palmitoyltransferase I in animal and human tissues. Biochem. J. 214:21-28.[Medline]
57. Sahlin, K. (1990) Muscle carnitine metabolism during incremental dynamic exercise in humans. Acta Physiol. Scand. 138:259-262.[Medline]
58. Carter, A. L., Lennon, D.L.F. & Stratman, F. W. (1981) Increased acetyl carnitine in rat skeletal muscle as a result of high-intensity short-duration exercise. Implication in the control of pyruvate dehydrogenase activity. FEBS Lett. 126:21-24.[Medline]
59. Harris, R. C., Louise Foster, C. V. & Hultman, E. (1987) Acetylcarnitine formation during intense muscular contraction in humans. J. Appl. Physiol. 63:440-442.
60. Krebs, H. A., Cornell, N. W., Lund, P. & Hems, R. (1974) Lundquist, F. Tygstrupp, N. eds. Regulation of Hepatic Metabolism, Alfred Benzon Symposium VI 1974:726 Munksgaard Copenhagen, Denmark. .
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