Digestion and Absoption of NAD by the Small Intestine of the Rat

Digestion and Absoption of NAD by the Small Intestine of the Rat

ABSTRACT A number of preparations of varying complexity have been used in an
effort to elucidate the reactions by which NAD is hydrolyzed to nicotinamide during
intestinal digestion. NAD labeled with 14Cin the adenine or pyridine moiety was the
substrate used with perfused rat intestine, live rats, perfused live rats, with collection
of portal flow, intestinal contents, mucosa! tissue, or pancreatic juice. The conclusions
reached are that a pyrophosphatase present in the intestinal juice and to a much lesser
extent in the pancreatic juice releases 5′-AMP and nicotinamide ribonucleotide. The 5′-
AMP was rapidly converted to adenosine then to inosine by bacteria-free intestinal
contents. Perfused or intact intestine rapidly hydrolyzed NMN to nicotinamide riboside,
which accumulated, but was not absorbed. It was slowly cleaved by an enzyme associated
with the mucosal cells to nicotinamide, which was the major if not the only labeled
compound absorbed.

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