Y. Kao et al., Effects of insulin on lipid metabolism of larvae and metamorphosing landlocked sea lamprey, Petromyzon marinus, GEN C ENDOC, 114(3), 1999, pp. 405-414
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.