title: Demonstration of hepatic cytosolic malic enzyme activity as a thyroid hormone sensitive physiologic parameter in a teleost, Heteropneustes fossilis bloch.
abstract: Single injections of various doses (0.1, 0.25, 0.5, 5 and 20 micrograms/g) of T3 significantly increased the cytosolic malic enzyme activity (delta OD/min/mg cytosolic protein) in liver of Singi fish Heteropneustes fossilis Bloch, in a dose-dependent nature, maximum up to 5 micrograms/g dose on the 3rd day in comparison to the control. There was no difference in the enzyme activity between 5 and 20 micrograms/g of T3 doses. When the enzyme activity was expressed per mg DNA, the dose-dependent increase in the malic enzyme activity was observed upto 0.5 microgram/g of T3, whereas a fall in the enzyme activity was noticed with 5 and 20 micrograms/g of T3 doses. Lowering the dose of T3 to 0.05 microgram/g was without any effect on the malic enzyme activity (delta OD/min/mg cytosolic protein or DNA). Hepatic cytosolic protein content showed a biphasic nature of variation, significant increase with single injections of 0.05, 0.1, 0.25 and 0.5 microgram/g and a fall with 5 and 20 micrograms/g of T3 doses in comparison to the untreated control. Cycloheximide treatments of the Singi fishes counteracted both the T3-induced rise in the hepatic cytosolic malic enzyme activity (delta OD/min/mg cytosolic protein or DNA) and the hepatic cytosolic protein contents. Thiourea-treated hypothyroid fishes showed significantly decreased level of malic enzyme activity (delta OD/min/mg cytosolic protein or DNA) and cytosolic protein content in liver. A single injection of T3 at 0.25 microgram/g to the thiourea-treated fishes not only recovered but also increased the enzyme activity and cytosolic protein content above the untreated control values.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D003513:Cycloheximide / Q000494:pharmacology; D003600:Cytosol / Q000201:enzymology*; D005399:Fishes / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008291:Malate Dehydrogenase / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism; D013890:Thiourea / Q000494:pharmacology; D013963:Thyroid Hormones / Q000494:pharmacology*; D014284:Triiodothyronine / Q000494:pharmacology
chemical_list: D011506:Proteins; D013963:Thyroid Hormones; D014284:Triiodothyronine; D003513:Cycloheximide; D008291:Malate Dehydrogenase; D013890:Thiourea