Diamine oxidase (histaminase). A circulating marker for rat intestinal mucosal maturation and integrity

Diamine oxidase (histaminase) is an enzyme found in high concentrations in the intestinal mucosa of humans and other mammalian species. The authors investigated whether plasma and mucosal levels of diamine oxidase activity reflect both the maturational status of the mucosa during its development in the newborn rat and the degree of mucosal damage during its injury in the adult rat. Litter mates were reared under identical conditions and killed at different ages from day 0 to day 40 after birth. Diamine oxidase in the small intestine was low at birth, increased gradually with age, reached a peak at 22 days, and then remained at normal adult levels, similar to the developmental patterns of maltase and sucrase. Plasma diamine oxidase rose in parallel with intestinal levels (n = 500, r = 0.84, P < 0.001), reached a peak at 24 days, and then remained at normal adult levels. Diamine oxidase activity in 15 nonintestinal tissues was < 5% of ileal mucosal activity, and no nonintestinal activities showed increase with age. Adult rat intestinal loops were perfused with hyperosmolar sodium sulfate solutions to produce selective damage to villus mucosa. With increasing mucosal damage, there was a progressive decrease in the enzyme activities studied; first, lactase levels fell, then maltase and sucrase, and finally mucosal and plasma diamine oxidase activity levels fell. The decrease in plasma diamine oxidase reflected the degree of mucosal damage (n = 29, P < 0.04). Diamine oxidase activity is thus unique among intestinal mucosal enzymes studied to date in that circulating levels can serve as a marker of mucosal maturation and integrity.