Study of the relationship between thyroid hormones and lipid metabolism during KClO4-induced metamorphosis of landlocked lamprey, Petromyzon marinus

This study examines the role of thyroid hormones (TH) (thyroxine and triiod othyronine) in regulating lipid metabolism of landlocked larval sea lamprey s, Petromyzon marinus. Larvae were treated with either thyroxine (0.5 or 1 mg l(-1) water) or triiodothyronine (0.25 or 1 mg l(-1) water) in the prese nce or absence of the goitrogen, potassium perchlorate (KClO4) (0.05% w/v), for 4, 8, and 16 weeks. Treatment with KClO4 alone, which induced metamorp hosis after 8 weeks and lowered plasma TH levels, reduced hepatic and renal total lipid content after 8 weeks of treatment. KClO4-induced lipid deplet ion after the 8-week treatment was supported by an increased rate of hepati c lipolysis, as indicated by increased triacylglycerol lipase activity. Fur thermore, reduced lipogenesis in the liver was indicated by decreased hepat ic acetyl-CoA carboxylase and diacylglycerol acyltransferase (DGAT) activit ies, and by decreased renal DGAT activity following 8 weeks of KClO4 treatm ent. Treatment of larvae for 4 weeks with TH alone resulted in either no ch ange or a slight increase of lipid in the liver and kidney. TH treatments i n combination with KClO4 failed to induce metamorphosis and, after up to 8 weeks, several TH treatments blocked changes in lipid content and enzyme ac tivity associated with KClO4-induced metamorphosis. These experimental resu lts suggest that TH deficiency during metamorphosis may promote lipid catab olism, while the presence of TH tends to protect/promote lipid reserves, pe rhaps favoring the larval condition. The actions of TH and KClO4 on metamor phosis-associated lipid metabolism in sea lampreys may be direct, permissiv e, and/or indirect via other factors. (C) 1999 Elsevier Science Inc. All ri ghts reserved.