Rat colon ornithine and arginine metabolism: coordinated effects after proliferative stimuli

Ornithine decarboxylase (ODC) catalyzes the first step in the polyamine bio synthetic pathway, a highly regulated pathway in which activity increases d uring rapid growth. Other enzymes also metabolize ornithine, and in hepatom as, rate of growth correlates with decreased activity of these other enzyme s, which thus channels more ornithine to polyamine biosynthesis. Ornithine is produced from arginase cleavage of arginine, which also serves as the pr ecursor for nitric oxide production. To study whether short-term coordinati on of ornithine and arginine metabolism exists in rat colon, ODC, ornithine aminotransferase (OAT), arginase, ornithine, arginine, and polyamine level s were measured after two stimuli (refeeding and/or deoxycholate exposure) known to synergistically induce ODC activity. Increased ODC activity was ac companied by increased putrescine levels, whereas OAT and arginase activity were reduced by either treatment, accompanied by an increase in both argin ine and ornithine levels. These results indicate a rapid reciprocal change in ODC, OAT, and arginase activity in response to refeeding or deoxycholate . The accompanying increases in ornithine and arginine concentration are li kely to contribute to increased flux through the polyamine and nitric oxide biosynthetic pathways in vivo.