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Article

Food Intake Abolishes the Response of Rat Jejunal Na⁺,K⁺-ATPase to Dopamine¹

Institute of Pharmacology and Therapeutics, Faculty of Medicine, 4200 Porto, Portugal

²To whom correspondence should be addressed.

	ABSTRACT

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The aim of the present study was to evaluate whether the sensitivity of jejunal Na⁺,K⁺-ATPase to inhibition by dopamine (DA) in young rats is related to the type of food (breast milk vs. solid) or reflects a developmental adaptation. When 18-d-old rats were separated from their dams and fed solid food (the same used to feed adult rats) for 2 d, intestinal Na⁺,K⁺-ATPase activity was significantly greater than that of breast-fed pups of the same age (20 d) (127 ± 8 vs. 52 ± 4 nmol Pi · mg protein^-1 · min^-1; P < 0.05). Activity in rats fed solid food was insensitive to inhibition by 1 µmol/L DA. Na⁺,K⁺-ATPase activity in 60-d-old rats (117.4 ± 4.2 nmol Pi · mg protein^-1 · min^-1) was also higher (P < 0.05) than in breast-fed rats, and DA (1 µmol/L) did not inhibit enzyme activity. The B_max value for binding of [³H]-Sch 23390 in 20-d-old breast-fed rats did not differ from that in age-matched rats fed a solid food for 2 d and or that in 60-d-old rats. Levels of DA, but not L-3,4-dihydroxyphenylalanine and amine metabolites, in the jejunal mucosa of 20-d-old rats that had eaten solid food for 2 d were 60% lower than in age-matched rats, breast-fed rats, and not different from those in the jejunal mucosa of 60-d-old rats fed the solid food. We conclude that in adult rats, in contrast to in young rats, DA does not inhibit jejunal Na⁺,K⁺-ATPase activity, and food intake in young rats plays an important role in the development of the insensitivity of Na⁺,K⁺-ATPase activity to DA.

KEY WORDS: • dopamine • jejunum • rats • Na⁺,K⁺-ATPase • food intake

	INTRODUCTION

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The current view of the intestinal dopaminergic system is that of a local nonneuronal system constituted by epithelial cells of intestinal mucosa rich in aromatic L-amino acid decarboxylase (AADC)³ activity and using circulating or luminal L-3,4-dihydroxyphenylalanine (L-DOPA) as a source for dopamine (DA) (Vieira-Coelho et al. 1997 ). DA is particularly abundant in the mucosal cell layer (Eaker et al. 1988 ; Esplugues et al. 1985 ), and studies on the formation of DA from exogenous L-DOPA along the rat digestive tract showed that the highest AADC activity is located in the jejunum (Vieira-Coelho and Soares-da-Silva 1993 ). Because the DA produced in this area is in close proximity to epithelial cells which contain receptors for the amine, it has been hypothesized that DA may act as a paracrine or autocrine substance (Vieira-Coelho et al. 1997 ). A high salt (HS) intake has been found to constitute an important stimulus for the production of DA in rat jejunal epithelial cells, and this is accompanied, in 20-d-old animals, by a decrease in sodium intestinal absorption (Finkel et al. 1994 ). This effect is accomplished, at the cellular level, by inhibition of Na⁺-K⁺-ATPase activity (Vieira-Coelho et al. 1998 ). The relative importance of this system in controlling sodium absorption assumes particular relevance in view of the findings that 40-d-old rats subjected to a HS intake have a fault in intestinal DA production during salt loading, in contrast to that occurring in 20-d-old animals. The lack of changes in the jejunal function in response to HS intake coincides with the period in which the renal function has reached maturation (Robillard et al. 1992 ), suggesting the occurrence of complementary functions between the intestine and the kidney during development.

In transporting epithelia, vectorial movement of sodium is accomplished by means of the Na⁺,K⁺-ATPase located at the basolateral plasma membrane and several sodium transport mechanisms localized at the apical domain of the cell (Rodriguez-Boulon and Nelson 1989 ). The basal activity of this pump and its modulation, which will reflect intestinal function (absorption and secretion), can be influenced by different factors, such as absence or presence of food in the intestine, protein and salt content in the diet, and stage of the developmental process (Binder 1983 ). This has a great impact during the uptake of nutrients and in the maintenance of electrolyte homeostasis and water metabolism during development (Herbst and Suskind 1969 , Younoszai et al. 1978 ).

The aim of the present study was to evaluate whether the sensitivity of Na⁺,K⁺-ATPase to inhibition by DA in young rats is related to the type of diet or reflects a developmental adaptation. For these purposes, young breast-fed rats were challenged with solid food, the same fed to adult rats.

	MATERIALS AND METHODS

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Animals.

All the experiments were performed in male Wistar rats (Harlan-Interfauna, Barcelona, Spain) that were 20-d-old (40–50 g) or 60-d-old (260–300 g). Rats were kept in air-conditioned animal quarters and had free access to drinking water until the day of the experiment. Rats were killed by decapitation under ether anesthesia. Young rats were divided in two groups: i) those separated from their dams and given the solid food for 2 d, and ii) breast-fed rats. Adult rats were fed the solid food. The solid food (rat maintenance diet, catalog number 9609) was obtained from Harlan-Teklad (Oxon, United Kingdom).

Cell isolation.

The method of cell isolation was similar to that previously described (Vieira-Coelho et al. 1998 ) with minor modifications. The jejunum was isolated and divided in small fragments. These were everted with fine forceps and incubated for 45 min in 5 mL warm (37°C) and gassed (95% O₂ and 5% CO₂) Hanks’ solution with 0.06% collagenase type I (Sigma Chemical Co., St. Louis, MO). At the end of the incubation period the fragments were removed from the solution, and the medium containing the detached cells was centrifuged (200 x g, 4°C) for 4 min, and the cell pellet was resuspended in Hanks’ solution. Cell viability was estimated by the Trypan blue (0.04%; 1 min) exclusion method, and the percentage of viable cells (excluding the dye), determined by hemocytometer counting, was > 90%.

Na⁺,K⁺-ATPase activity.

Na⁺,K⁺-ATPase activity was measured by the method of Quigley and Gotterer (1969) and adapted in our laboratory with slight modifications. Briefly, isolated jejunal epithelial cells, obtained as described above, were preincubated for 20 min at 37°C. After the preincubation period the jejunal epithelial cells were permeabilized by rapid freezing in dry ice-acetone and thawing. The reaction mixture contained (in mmol/L) 37.5 imidazole buffer, 75 NaCl, 5 KCl, 1 sodium EDTA, 5 MgCl₂, 6 NaN₃, 75 tris(hydroxymethyl)aminomethane(tris) hydrochloride and 100 µL cell suspension (100 µg protein). The reaction was initiated by the addition of 4 mmol/L ATP (25 µL). For determination of ouabain-sensitive ATPase, NaCl and KCl were omitted, and ouabain (1 mmol/L; 100 µL) or vehicle (water; 100 µL) was added to the assay. After incubation at 37°C for 15 min, the reaction was terminated by the addition of 50 µL of ice-cold trichloroacetic acid. Samples were centrifuged (1,500 x g), and liberated P_i (free phosphorus) in the supernatant was measured by spectrophotometry at 740 nm. Na⁺,K⁺-ATPase activity is expressed as nanomoles P_i per milligram protein per minute and determined as the difference between total and ouabain-insensitive ATPase. The protein concentration in cell suspensions (~2 g/L), as determined by the method described by Bradford (1976) with human serum albumin as a standard, was similar in all samples.

Radioligand binding.

Membranes from intestinal mucosa were obtained from 20-d-old breast-fed rats, 18-d-old rats separated from their dams and given the solid food for 2 d, and 60-d-old rats fed solid food. After killing, a segment of jejunum (5–10 cm) was removed, opened longitudinally along the mesenteric border and rinsed free from the alimentary contents with cold saline (9 g/L NaCl), and the jejunal mucosa was removed with a scalpel. The mucosa thus obtained was homogenized in 10 mmol/L Tris-HCl, pH 7.4, containing 250 mmol/L sucrose, 1 mmol/L PMSF, 1 mmol/L EDTA and 5 mg/L each of leupeptin and pepstatine, with a Potter-Elvehjem Teflon homogenizer, and centrifuged (20,000 x g, 20 min, 4°C). Pellets were resuspended to a concentration of 2 g protein · L^-1 in 10 mmol · L^-1 Tris-HCl, pH 7.4 with 5 mmol/L MgCl₂ and 250 mmol/L sucrose and stored aliquoted at –80°C. Membranes were thawed at room temperature, centrifuged (20,000 x g, 20 min, 4°C) and resuspended in binding buffer (in mmol/L: 50 Tris-HCl, 120 NaCl, 5 KCl, 2 CaCl₂ and 1 MgCl₂, pH = 7.4). Saturation experiments were performed in four replicates in 96-well EIA/RIA plates (Costar) in a final volume of 0.2 mL respective binding buffer containing 0.1–10 nmol/L [³H]-Sch 23390 and 100–200 µg membrane protein. Nonspecific binding was determined in the presence of 10 µmol/L of unlabeled Sch 23390. After a 30-min incubation at 30°C in a shaking water bath, assays were terminated by vacuum filtration through glass fiber filter mats with the Brandel 96 cell Harvester (Brandel, Gaithersburg, MD). Filters were washed three times with 200 µL of cold 50 mmol/L Tris-HCl pH 7.4, dried and impregnated with MeltiLex A (Wallac, Finland) and radioactivity measured in a Microbeta counter (model 1450; Wallac, Finland).

Assay of monoamines.

The assays for DA, norepinephrine, 5-hydroxytrptamine (5-HT) and metabolites were performed by means of HPLC, as previously described (Soares-da-Silva et al. 1996 ). The detection was carried out electrochemically with a glassy carbon electrode, an Ag/AgCl reference electrode and an amperometric detector (Gilson model 141); the detector cell was operated at 0.75 V. The current produced was monitored using the Gilson 712 HPLC software. The lower limit for detection of L-DOPA, DA, 3,4-dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3-MT), homovanillic acid (HVA), norepinephrine, 5-HT and 5-hydroxyindolacetic acid (5-HIAA) ranged between 350 to 1,000 fmol.

Drugs.

The compounds used were DA hydrochloride, 5-HT hydrochloride, ouabain and pargyline hydrochloride, obtained from Sigma Chemical Company. Quinerolane, SKF 83566, SKF 38393 and (S)-sulpiride were obtained from Research Biochemicals International (RBI, Natick, MA). The radioligand [³H]-Sch 23390 ([N-methyl-³H]R[+]-7-chloro-2,3,4,5-tetrahydro-3-methyl-1-phenyl-1H-3-benzazepine-8-ol, specific activity 2600–3200 GBq/mmol was purchased from New England Nuclear (Boston, MA). Tolcapone was kindly donated by late Professor Mosé Da Prada (Hoffman La Roche, Basel, Switzerland).

Statistics.

Results are means ± SEM for the indicated number of determinations. [³H]-Sch 23390 saturation parameters, B_max and K_D, were obtained with nonlinear iterative curve-fitting algorithms using the GraphPad Prism statistics software package (Motulsky et al. 1994 ). Statistical analysis was performed by one-way ANOVA followed by Student’s t test for unpaired comparisons. A P-value < 0.05 denoted a significant difference.

	RESULTS

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Basal jejunal Na⁺,K⁺-ATPase activity in 20-d-old breast-fed rats was considerably lower (P < 0.05) than that in age-matched rat fed solid food for 2 d (Fig. 1 ). This dramatic difference in jejunal Na⁺,K⁺-ATPase activity was accompanied by loss of sensitivity to the inhibitory effects of DA. DA (1 µmol/L) significantly inhibited jejunal Na⁺,K⁺-ATPase activity in breast-fed 20-d-old rats, but not in aged-matched rats fed solid food (Fig. 2 ). The inhibitory effect of DA (1 µmol/L) on jejunal Na⁺,K⁺-ATPase activity in breast-fed 20-d-old rats was abolished by pretreatment with the selective D₁ receptor antagonist SKF 83566 (1 µmol/L), but not by the selective D₂ receptor antagonist S-sulpiride (1 µmol/L). The selective D₁ receptor agonist SKF 38393 (10 nmol/L) inhibited jejunal Na⁺,K⁺-ATPase activity in breast-fed 20-d-old rats, but not in aged-matched rats fed solid food. Basal jejunal Na⁺,K⁺-ATPase activity in 60-d-old rats was 2.5-fold that of 20-d-old breast-fed rats, but not different from that in 20-d-old rats fed solid food for 2 d (Fig. 1) . In 60-d-old rats, DA (1 µmol/L), the selective D₁ receptor agonist SKF 38393 (10 nmol/L) and the selective D₂ receptor agonist quinerolane (10 nmol/L) did not inhibit jejunal Na⁺,K⁺-ATPase activity (data not shown).

View larger version (35K): [in this window] [in a new window]   Figure 1. Basal jejunal Na+, K+-ATPase activity in 20-d-old breast-fed rats and age-matched rats fed solid food for 2 d and in 60-d-old rats. Columns represent means of four rats per group; vertical lines indicate SEM Significantly different from corresponding values for 20-d-old breast-fed rats (* P < 0.05).

View larger version (48K): [in this window] [in a new window]   Figure 2. Jejunal Na+, K+-ATPase activity in 20-d-old (A) breast-fed rats and (B) age-matched rats feed for 2 d solid food in the absence and the presence of dopamine (DA) (1 µmol/L), DA (1 µmol/L) + SKF 83 566 (1 µmol/L), DA (1 µmol/L) + S-sulpiride (1 µmol/L) and SKF 38 393 (10 nmol/L). Columns represent means of four rats per group; vertical lines indicate SEM Significantly different from corresponding values for control (* P < 0.05).

View larger version (31K): [in this window] [in a new window]   Figure 3. Specific binding of [3H]-Sch23390 (0.1–9 nmol/L) to membranes from intestinal mucosa of 20-d-old breast-fed rats or fed solid food, and 60-d-old rats. The inset graph represents a Scatchard plot with amount bound (fmol · mg protein-1) in ordinates and the abscissa represents the ratio amount bound/free ligand (fmol · mg protein-1 · nmol/L). Symbols represent means of five experiments with four replicate determinations and vertical lines show SEM

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

Because basal Na⁺,K⁺-ATPase activity in 20-d-old rats fed solid food for 2 d was higher than in breast-fed rats, we hypothesized that the loss of sensitivity to DA in the former rats was related to the high level of enzyme activity. However, in adult, food-deprived rats, which have lower basal Na⁺,K⁺-ATPase activity than fed rats, DA still was not inhibitory (Lucas-Teixeira et al. 1999 ). In fact, a low basal Na⁺,K⁺-ATPase activity after food deprivation for 48 h is consistent with a previous report (Murray and Wild 1980 ), with the low activity being completely reverted by refeeding. As previously described in 40-d-old Sprague-Dawley rats (Vieira-Coelho et al. 1998 ), DA did not inhibit Na⁺,K⁺-ATPase in 60-d-old Wistar rats. These differences appear not to be related to differences in the density of DA receptors, since the density of D₁ binding sites did not differ in young and adult rats.

Differences in basal Na⁺,K⁺-ATPase activity between young breast-fed rats and age-matched rats fed solid food may be related to different salt or protein contents of the diets (maternal milk vs. solid food). Both sodium and amino acids affect renal Na⁺,K⁺-ATPase activity (Bertorello et al. 1988 ; Jakobsson et al. 1990 ). However, basal Na⁺,K⁺-ATPase activity in young rats fed HS was lower than in rats fed no salt, without differences in sensitivity to inhibition by DA (Vieira-Coelho et al. 1998 ). This change in basal Na⁺,K⁺-ATPase activity during HS intake was completely reverted by pretreatment with benserazide, a AADC inhibitor, suggesting that it was related to the enhanced availability of DA. In fact, HS intake was demonstrated in 20-d-old rats to increase the formation of DA in the jejunal mucosa (Finkel et al. 1994 ; Vieira-Coelho et al. 1998 ). The finding that DA levels in the jejunal mucosa of breast-fed rats were higher than in rats fed the solid diet suggests that the high Na⁺,K⁺-ATPase activity may be related to low inhibitory dopaminergic tonus upon the enzyme. Another observation supporting the view of low jejunal dopaminergic tonus in 20-d-old rats fed solid food is that the low levels of DA were not accompanied by a change in the density of D₁ binding sites. This apparently conflicts with the result that jejunal Na⁺,K⁺-ATPase activity in 20-d-old rats fed the solid food was not sensitive to exogenous DA or D₁ receptor stimulation. Perhaps the solid food contains an unknown substance which impairs the response of Na⁺,K⁺-ATPase to DA and simultaneously alters the availability of endogenous DA.

The intestinal nonneuronal dopaminergic system and its effects on the regulation of electrolyte transport, especially sodium absorption, have been recently described (Finkel et al. 1994 , Vieira-Coelho et al. 1997 and 1998 ). There are similar properties in this autocrine/paracrine intestinal system and the kidney nonneuronal dopaminergic system (Soares-da-Silva 1994 ), where diuretic and natriuretic effects of DA are well known (Aperia 1994 , Jose et al. 1992 , Lee 1993 , Lokhandwala and Hegde 1991 ). Epithelial cells from both renal proximal tubules and the intestinal mucosa are endowed with i) efficient mechanisms for L-DOPA uptake, ii) high AADC activity, which easily converts intracellular L-DOPA to DA, iii) efficient enzyme systems for the metabolic degradation of newly-formed DA and iv) specific receptors for the amine, the activation of which leads to Na⁺,K⁺-ATPase inhibition and transepithelial sodium flux. In the two systems, the final effect on sodium is the same, there is a decrease in sodium absorption in the intestine and an increase in sodium excretion in the kidney. Because defective responses to DA receptor activation might lead to sodium retention and increased blood pressure, these nonneuronal dopaminergic systems are physiologically relevant (Hussain and Lokhandwala 1998 , Jose et al. 1998 ).

In conclusion, DA inhibits jejunal Na⁺,K⁺-ATPase in young breast-fed Wistar rats through activation of D₁ receptors, but not in adult rats or in young rats fed solid food for 2 d. The lack of DA sensitivity is accompanied by markedly elevated basal jejunal Na⁺,K⁺-ATPase activity.

	FOOTNOTES

 
¹ Supported by grant PECS/S/SAU/14010/98 from Fundação Ciência Tecnologia.

³ Abbreviations used: AADC, aromatic L-amino acid decarboxylase; DA, dopamine; DOPAC, 3,4-dihydroxyphenylacetic acid; 5-HIAA, 5-hydroxyindolacetic acid; HS, high salt; 5-HT, 5-hydroxytryptamine; HVA, homovanillic acid; L-DOPA, L-3,4-dihydroxyphenylalanine; 3-MT, 3-methoxytyramine; NE, norepinephrine.

Manuscript received May 21, 1999. Initial review completed September 8, 1999. Revision accepted December 14, 1999.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 

1. Aperia A. Dopamine action and metabolism in the kidney. Curr. Opin. Nephrol. Hypertens. 1994;3:39-45[Medline]

2. Bertorello A., Hokfelt T., Goldstein M., Aperia A. Proximal tubule Na+-K+-ATPase activity is inhibited during high-salt diet: evidence for DA-mediated effect. Am. J. Physiol. 1988;254:F795-F801[Abstract/Free Full Text]

3. Binder H. J. Absorption and secretion of water and electrolytes by small and large intestine. Sleisinger O. Fordtran O. eds. Gastrointestinal Disease 1983:812-829 Saunders Philadelphia, PA.

4. Bradford M. M. A rapid method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal. Biochem. 1976;72:248-254[Medline]

5. Eaker E. Y., Bixler G. B., Dunn A. J., Moreshead W. V., Mathias J. R. Dopamine and norepinephrine in the gastrointestinal tract of mice and the effects of neurotoxins. J. Pharmacol. Exp. Ther. 1988;244:438-442[Abstract/Free Full Text]

6. Esplugues J. V., Caramona M. M., Moura D., Soares-da-Silva P. Effects of chemical sympathectomy on dopamine and noradrenaline content of the dog gastrointestinal tract. J. Auton. Pharmacol. 1985;5:189-195[Medline]

7. Finkel Y., Eklof A. C., Granquist L., Soares-da-Silva P., Bertorello A. M. Endogenous dopamine modulates jejunal sodium absorption during high-salt diet in young but not in adult rats. Gastroenterol 1994;107:675-679[Medline]

8. Herbst J. J., Suskind P. Postnatal development of the small intestine of the rat. Pediatr. Res. 1969;3:27-33

9. Hussain T., Lokhandwala M. F. Renal dopamine receptor function in hypertension. Hypertension 1998;32:187-197[Abstract/Free Full Text]

10. Jakobsson B., Larsson S. H., Wieslander A., Aperia A. Amino acid stimulation of Na,K-ATPase activity in rat proximal tubule after high-protein diet. Acta Physiol. Scand. 1990;139:9-13[Medline]

11. Jose P. A., Eisner G. M., Felder R. A. Renal dopamine receptors in health and hypertension. Pharmacol. Ther. 1998;80:149-182[Medline]

12. Jose P. A., Raymond J. R., Bates M. D., Aperia A., Felder R. A., Carey R. M. The renal dopamine receptors. J. Am. Soc. Nephrol. 1992;2:1265-1278[Abstract]

13. Kansra V., Hussain T., Lokhandwala M. F. Alterations in dopamine DA₁ receptor and G proteins in renal proximal tubules of old rats. Am. J. Physiol. 1997;42:F53-F59

14. Lee M. R. Dopamine and the kidney: ten years on. Clin. Sci. 1993;84:357-375[Medline]

15. Lokhandwala M. F., Hegde S. S. Cardiovascular pharmacology of adrenergic and dopaminergic receptors: therapeutic significance in congestive heart failure. Am. J. Med. 1991;90:2.S-9S

16. Lucas-Teixeira V., Vieira-Coelho M. A., Soares-da-Silva P. Effect of food intake on the response of jejunal Na+,K+-ATPase to dopamine. FASEB J 1999;13:A1012

17. Marmon L. M., Albrecht F., Canessa L. M., Hoy G. R., Jose P. A. Identification of dopamine1A receptors in the rat small intestine. J. Surg. Res. 1993;54:616-620[Medline]

18. Motulsky, H. J., Spannard, P. & Neubig, R. (1994) GraphPad Prism (version 1.0). GraphPad Prism Software Inc., San Diego, CA.

19. Murray D., Wild G. E. Effect of fasting on Na-K-ATPase activity in rat small intestinal mucosa. Can. J. Physiol. Pharmacol. 1980;58:643-649[Medline]

20. Quigley J. P., Gotterer G. S. Distribution of Na,K-stimulated ATPase activity in rat intestinal mucosa. Biochim. Biophys. Acta 1969;173:456-468[Medline]

21. Robillard J., Segar J., Smith F., Guillery E., Jose P. Mechanisms regulating renal sodium excretion during development. Pediatr. Nephrol. 1992;6:205-213[Medline]

22. Rodriguez-Boulon E., Nelson W. J. Morphogenesis of the polarized epithelial cell phenotype. Science 1989;107:718-725

23. Soares-da-Silva P. Source and handling of renal dopamine: Its physiological importance. News in Physiological Sci 1994;9:128-134

24. Soares-da-Silva P., Vieira-Coelho M. A., Pestana M. Antagonistic actions of renal dopamine and 5-hydroxytryptamine: endogenous 5-hydroxytryptamine, 5-HT1A receptors and antinatriuresis during high sodium intake. Br. J. Pharmacol. 1996;117:1193-1198[Medline]

25. Vieira-Coelho M. A., Gomes P., Serrão M. P., Soares-da-Silva P. Renal and intestinal autocrine monoaminergic systems: dopamine versus 5-hydroxytryptamine. Clin. & Exp. Hypertens. 1997;19:43-58

26. Vieira-Coelho M. A., Lucas-Teixeira V. A., Finkel Y., Soares-da-Silva P., Bertorello A. M. Dopamine-dependent inhibition of jejunal Na⁺,K⁺-ATPase during high-salt diet in young but not in adult rats. Am. J. Physiol. 1998;275:G1317-G1323[Abstract/Free Full Text]

27. Vieira-Coelho M. A., Soares-da-Silva P. Dopamine formation, from its immediate precursor 3,4-dihydroxyphenylalanine, along the rat digestive tract. Fund. Clin. Pharmacol. 1993;7:235-243[Medline]

28. Younoszai M. K., Sapario R. S., Laughlin M. Maturation of jejunum and ileum in rats. J. Clin. Invest. 1978;68:271-280

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