Intestinal absorption and excretion of octapeptides composed of D amino acids.
Octapeptides synthesized from D amino acids were absorbed from the intestine and excreted in urine of normal rats drinking 5% glucose/1% creatinine containing the 125I-labeled peptides at 0.1-25 mg/dl. The rats ingested fluid at the rate of about 20 ml/hr and produced urine at 15 ml/hr for several hours during the nocturnal feeding period. Sixty-one +/- 4% of the ingested creatinine and 50 +/- 3% of a lipid-insoluble D octapeptide (EASASYSA, 784 Da) were excreted intact in the urine. The steady-state molar rate of absorption-excretion of creatinine equaled or exceeded the maximum rate of carrier-mediated intestinal transport of glucose, suggesting that both the creatinine and the D octapeptide were transported paracellularly by solvent drag through absorptive cell junctions that were dilated by the glucose. More than 70% of the ingested glucose was also absorbed paracellularly. The results demonstrate that intact oligopeptides can be absorbed efficiently from the intestine when they are not hydrolyzed by membrane-bound peptidases of the brush border. The results also provide support for recent theories proposing that coupling of membrane digestion with paracellular solvent drag accounts for a major fraction of normal intestinal absorption of nutrients.
Pappenheimer
J R
JR
Department of Biology, Harvard University, Bedford, MA 01730.
Dahl
C E
CE
Karnovsky
M L
ML
Maggio
J E
JE
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D001693:Biological Transport, Active; D003404:Creatinine / Q000493:pharmacokinetics / Q000652:urine; D005243:Feces / Q000737:chemistry; D005260:Female; D005947:Glucose / Q000493:pharmacokinetics; D007408:Intestinal Absorption; D008297:Male; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry / Q000493:pharmacokinetics* / Q000652:urine; D051381:Rats; D013237:Stereoisomerism
D000596:Amino Acids; D009842:Oligopeptides; D003404:Creatinine; D005947:Glucose