ORNITHINE DECARBOXYLASE ALONG THE MOUSE AND RAT NEPHRON

Renal arginase activity is a potent source of ornithine (Orn) for poly amine synthesis. Ornithine decarboxylase (ODC) was localized along the mouse and rat nephron by incubating viable nephron segments isolated by microdissection from collagenase-treated kidneys with or without D, L-2-(difluoromethyl)ornithine (DFMO), a selective inactivator of ODC. Tubules from either control or DFMO-treated animals were incubated wit h 100 mu M L-[1-C-14]Orn. In control mice, Orn decarboxylation occurre d mainly in the proximal convoluted tubule (PCT). In DFMO-treated mice , Orn decarboxylation was dramatically reduced in PCT and in proximal straight tubules (PST). In rats, Orn decarboxylation also occurred pre dominantly in the proximal tubule. Addition of 10 mM DFMO to isolated tubules dramatically decreased Orn decarboxylation in PCT and in PST. Thereafter, ODC activity was demonstrated in permeabilized tubules. In Triton X-100-treated tubules from control mice, ODC was exclusively f ound in proximal tubules (PCT > PST). This ODC activity was strongly i nhibited in DFMO-treated mice. In conclusion, the highest ODC activity was found in rat and mouse PCT, a segment devoid of arginase. We hypo thesize that the filtered Orn, which is reabsorbed along the PCT, is t he main source of Orn for ODC.