title: Differential effects of L-thyroxine on cardiac and hepatic monoamine oxidase activity toward benzylamine and serotonin.
abstract: Male and female rats of 2 age groups were given subcutaneous injections of L-thyroxine (500 mug/kg) at 12 h intervals for a period of 10 days. The activity of monoamine oxidase (MAO) in normal and thyrotoxic rats was studied with two substrates: benzylamine and serotonin. The results showed that a thyroxine effect on cardiac and liver MAO activity is dependent on the substrate used in the assay. Kinetic studies of cardiac and liver MAO after thyroxine-treatment showed an unaltered Km for benzylamine but a change in Km for serotonin. Both findings may indicate a discriminative action of thyroid hormones on different forms of MAO. The possible presence of a soluble activator and inhibitor for MAO was investigated.
mesh_terms: D000367:Age Factors; D000818:Animals; D005260:Female; D006321:Heart / Q000187:drug effects*; D006980:Hyperthyroidism / Q000139:chemically induced / Q000201:enzymology; D008099:Liver / Q000187:drug effects* / Q000201:enzymology; D008297:Male; D008995:Monoamine Oxidase / Q000378:metabolism*; D009206:Myocardium / Q000201:enzymology; D051381:Rats; D012701:Serotonin; D012737:Sex Factors; D013974:Thyroxine / Q000494:pharmacology*
chemical_list: D012701:Serotonin; D008995:Monoamine Oxidase; D013974:Thyroxine