title: Regulation of thyroid ornithine decarboxylase by the polyamines. Induction of a protein inhibitor of ornithine decarboxylase by the end-products of the reaction.
abstract: When spermidine, putrescine or 1,3-diaminopropane was injected (12.5 mumol/100 g body weight) into rats 1 h before thyrotropin, ornithine decarboxylase activity was increased by 75--150% over control levels. However, when greater than or equal to 75 mumol polyamine/100 g body weight was injected, thyrotropin-activated activity was inhibited by 70--95%. Multiple polyamine injections inhibited goitrogen-induced activity and gland weight increase by approx 35%. The polyamines also inhibited thyrotropin-activated rat thyroid ornithine decarboxylase in vitro in a dose-related fashion, with 50% inhibition occurring at 2--5 . 10(-4)M. The inhibition was not due to a direct effect on the enzyme. No stimulation was seen with low concentrations of polyamine. The polyamines had no effect on in vitro thyroid protein/RNA synthesis or glucose oxidation but had a biphasic effect on plasma membrane adenylate cyclase activity. A protein inhibitor to thyroid ornithine decarboxylase was generated in vivo by multiple injections of the polyamines into rats and in vitro by incubating bovine thyroid slices with 2--10 mM polyamine. The inhibitor was non-dialyzable, destroyed by boiling, and its formation was blocked in a dose-related fashion by cycloheximide. We conclude that: (1) thyroid ornithine decarboxylase is subject not only to positive control, but is also negatively regulated by its end-products, the polyamines, which induce a protein inhibitor to ornithine decarboxylase; (2) since gland growth is also inhibited under these conditions, the polyamine effect on thyroid ornithine decarboxylase may be biologically significant.
mesh_terms: D000818:Animals; D002262:Carboxy-Lyases / Q000037:antagonists & inhibitors*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000378:metabolism; D008297:Male; D009955:Ornithine Decarboxylase / Q000378:metabolism; D065108:Ornithine Decarboxylase Inhibitors; D011073:Polyamines / Q000494:pharmacology*; D011700:Putrescine / Q000494:pharmacology; D051381:Rats; D013095:Spermidine / Q000494:pharmacology; D013961:Thyroid Gland / Q000201:enzymology*; D013972:Thyrotropin / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D065108:Ornithine Decarboxylase Inhibitors; D011073:Polyamines; D013972:Thyrotropin; D002262:Carboxy-Lyases; D009955:Ornithine Decarboxylase; D013095:Spermidine; D011700:Putrescine