Effects of insulin on lipid metabolism of larvae and metamorphosing landlocked sea lamprey, Petromyzon marinus

This study was designed to examine the role of insulin (INS) in regulating changes in lipid metabolism of larval and metamorphosing landlocked lamprey , Petromyzon marinus. Larvae and stage 6 metamorphosing individuals were in jected intraperitoneally once per day for 2 days with either saline (0.6%), bovine INS (100 ng/g body weight), or alloxan (0.2 mg/g body weight). Insu lin administration resulted in depressed plasma fatty acid (FA) levels, whe reas alloxan injection elevated plasma FA levels at both life cycle interva ls. In larvae, INS-induced hypolipidemia was attended by increased lipid co ncentration in kidney and muscle, reduced rates of lipolysis in kidney, liv er, and muscle las indicated by decreased triacylglycerol lipase activity), and, to a lesser extent, by higher rates of lipogenesis in kidney and musc le las evidenced by higher acetyl-CoA carboxylase and/or diacylglycerol acy ltransferase activities). In general, the effects of alloxan were opposite of those of INS. The alloxan-induced increase in plasma FA was supported by an enhanced rate of lipolysis in the kidney, a relatively lower rate of fa tty acid synthesis in kidney, liver, and muscle, and a relatively lower ren al rate of TG synthesis. In stage 6 metamorphosing lamprey, the INS-induced decline in plasma FA was attended by reduced renal and hepatic rates of li polysis and by enhanced lipogenesis, as indicated by increased renal and he patic rates of de novo fatty acid synthesis and hepatic and muscular rates of TG synthesis. In contrast, the increase in plasma FA induced by alloxan in stage 6 animals was supported by reduced TG synthsis in liver. Immunocyt ochemistry revealed that alloxan was not cytotoxic to pancreatic beta cells , suggesting that the effects of alloxan were extrapancreatic in the time f rame of our study. Because insulin-induced lipogenesis and antilipolysis is similar to the pattern of lipid metabolism (phase I) displayed by lamprey during their spontaneous metamorphosis, INS may play a role, possibly in co ncert with other factors, in coordinating metamorphosis-associated changes in lipid metabolism. (C) 1999 Academic Press.