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Urea synthesis in enterocytes of developing pigs

G Wu1

  • 1Department of Animal Science and Faculty of Nutrition, Texas A&M University, College Station 77843-2471, USA.

The Biochemical Journal
|December 15, 1995
PubMed
Summary

Urea synthesis occurs in pig enterocytes after weaning, not before. This process, driven by increased arginase activity, helps protect against ammonia toxicity in the gut.

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Area of Science:

  • Biochemistry
  • Developmental Biology
  • Gastroenterology

Background:

  • Enterocytes play a crucial role in nutrient metabolism and waste detoxification within the gastrointestinal tract.
  • Ammonia is a potentially toxic byproduct of intestinal metabolism, originating from dietary sources, microbial activity, and amino acid breakdown.
  • The urea cycle is primarily known to occur in the liver, detoxifying ammonia into urea.

Purpose of the Study:

  • To investigate the developmental changes in urea synthesis capacity within pig enterocytes.
  • To determine the specific urea cycle enzymes involved in enterocyte urea production.
  • To elucidate the physiological significance of enterocyte urea synthesis in post-weaning pigs.

Main Methods:

  • Enterocytes were isolated from pigs at different developmental stages (newborn, suckling, post-weaning).
  • Urea synthesis rates were measured using radiolabeled precursors or by quantifying urea production from ammonia, glutamine, and arginine.
  • Activities of key urea cycle enzymes (carbamoyl phosphate synthase I, ornithine carbamoyltransferase, argininosuccinate synthase, argininosuccinate lyase, and arginase) were assayed.

Main Results:

  • No significant urea synthesis was detected in enterocytes from newborn or suckling pigs.
  • Enterocytes from post-weaning pigs exhibited significant, dose-dependent urea and ornithine production from ammonia, glutamine, and arginine.
  • Enzyme activity analysis revealed a substantial increase in arginase and argininosuccinate synthase, but not other urea cycle enzymes, in post-weaning pig enterocytes.

Conclusions:

  • Pig enterocytes gain the capacity for urea synthesis post-weaning, primarily due to a significant induction of arginase activity.
  • This enterocyte-specific urea synthesis pathway may serve as a protective mechanism against ammonia toxicity arising from intestinal glutamine metabolism and luminal sources.
  • The findings highlight a previously unrecognized role for enterocytes in ammonia detoxification in the developing gut.

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