J V Leonard, T. Marrs, J. M. Addison
Apr 1, 1976
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Journal
Pediatric Research
Abstract
Extract: This paper reports the investigation of a case of Hartnup disorder, in which tolerance tests were carried out with a mixture of free amino acids simulating casein and a partial enzymic hydrolysate of casein containing small peptides. The investigation also included measurement of renal clearances of amino acids. The patient, a girl aged 26 months, was given by mouth 5 g amino acid mixture in water, blood samples being taken before the dose and at 15, 30, and 45 min after the dose. The procedure was repeated with an equivalent dose (4.7 g) of the enzymic hydrolysate, containing the same amount of nitrogen. The results were compared with those from six normal adults Who were given 10 g amino acid mixture and on another occasion an equivalent dose of an enzymic hydrolysate of casein containing small peptides. In the adults, the increments in the plasma level of a given amino acid were similar whether the amino acid mixture or the enzymic hydrolysate was given. In the patient, a different pattern was seen. In some cases (Lys, Arg, and Pro) there was a large increase in plasma levels after both the amino acid mixture and the enzymic hydrolysate, as in the adult controls. In others (Gly, His, Tyr, Ser, Glu) there was no increase or a decrease in plasma levels after the amino acid mixture, but an increase after the enzymic hydrolysate. In a third category (Ala, Val, Leu, He, Met, Phe), increments after the enzymic hydrolysate were greater than after the amino acid mixture. The results with Thr were unexpected: after the amino acid mixture there was an initial rise in plasma levels and after the enzymic hydrolysate an initial fall. Renal clearances of Pro, Glu, Asp, and Lys were normal and those of Arg and Gin were slightly increased. The clearance of Gly was slightly increased and the clearances of His, Tyr, Ser plus Asn, Ala, Val, Leu, He, Met, Phe, and Thr were greatly increased. The results suggest the following. Absorption of free Lys, Arg, and Pro was normal. Absorption of free Gly, His, Tyr, and Ser was probably severely impaired and that of Val, Leu, He, Met, and Phe probably subnormal. Absorption of Glu and Ala was probably also subnormal. We cannot account for the results obtained with Thr. The results indicate that many neutral amino acids are malabsorbed in Hartnup disorder, and that free Glu may also be malabsorbed. Amino acids which are poorly absorbed in the free form are better absorbed from peptides. Most of the amino acids with a substantial increase in renal clearance also provided evidence of malabsorption. The finding of an increased renal clearance of Gly agrees with several previous observations in Hartnup disorderSpeculation: It is now known that di- and tripeptides are taken up intact by the absorptive cells of the small intestine, in addition to free amino acids. After uptake, the peptides undergo hydrolysis. Previous investigations in Hartnup disorder and cystinuria, combined with physiologic investigations, have shown that mucosal uptake of small peptides is independent of that of amino acids. The present investigation of a case of Hartnup disorder suggests that although many neutral amino acids are poorly absorbed in this condition when given in the free form, absorption of all these “affected” amino acids is better when given in peptide form. It appears that the peptide uptake system or systems of the intestinal mucosa are unaffected by the transport defect of Hartnup disorder, and that this is the explanation of the ability of the patients to maintain a reasonable state of nutrition when on an adequate diet, and of the frequent absence of obvious evidence of intestinal disturbance …