Gastrointestinal luminal polyamines: cellular accumulation and enterohepatic circulation.

The concentration of polyamines contained in the lumen of the gut was quantified. The duodenum and jejunum of the rat contained 2-3 mM putrescine and 1-2 mM cadaverine, whereas in the ileum and colon the concentration of these polyamines was significantly less. In addition, the concentrations of spermine and spermidine in the intestinal lumen were low to undetectable. Putrescine in the lumen of the gut was over 90% free with only 10% or less bound to protein. The activity of the enzymes responsible for the synthesis of polyamines was also measured. In contrast to concentration, enzyme activity was found to be high in the ileum, cecum, and colon and nonexistent in the duodenal and jejunal lumen. This suggested the potential for enterohepatic circulation of polyamines that were synthesized by the colonic microflora and transported to the proximal gut via the portal circulation and biliary tree. Indeed, when [14C]putrescine was instilled into the lumen of the gut, it was secreted in pancreaticobiliary secretions. Upper and lower jejunum and colon all supported enterohepatic circulation of polyamines, whereas it was absent in the ileum. Polyamine accumulation in IEC-6 cells grown under in vitro conditions was also measured. Putrescine was transported under time- and temperature-dependent but sodium-independent conditions. The transporter displayed little selectivity for the various polyamines and compounds with related structures but did not recognize amino acids. The Michaelis constant for putrescine accumulation was 1.26 x 10(-6) M with a maximal velocity of the enzyme reaction of 5,184 pmol putrescine.mg protein-1.h-1.(ABSTRACT TRUNCATED AT 250 WORDS)