Expression of arachidonate 12-lipoxygenase in rat tissues: A possible rolein glucagon secretion

There are three isoforms of arachidonate 12-lipoxygenase in mammals: platel et, leukocyte, and epidermal types. We found in this study that the leukocy te-type enzyme was present in rat pineal gland, lung, spleen, aorta, adrena l gland, spinal cord, and pancreas, as assessed by RT-PCR. Immunohistochemi cal analysis showed that the enzyme was localized in macrophages in lung an d spleen, alpha-cells of pancreatic islet, zona glomerulosa cells of adrena l cortex, and neuronal cells of spinal cord and superior cervical ganglion. The presence of the 12-lipoxygenase in pancreatic alpha-cells was confirme d by glucagon staining in a consecutive section. We overexpressed the leuko cyte-type 12-lipoxygenase cDNA in a glucagon-secreting alpha TC clone 6 cel l line that had been established from a transgenic mouse. Glucagon secretio n was stimulated by approximately twofold in the 12-lipoxygenase-expressing cells compared to the mock-transfected and original cells. The results sug gest that the 12-lipoxygenase of the leukocyte type augments glucagon secre tion from pancreatic islets.