Beta- and alpha-adrenergic mechanisms are involved in regulating type II thyroxine 5'-deiodinase in rat thymus.
The role of adrenergic receptors in regulation of rat thymus type II thyroxine 5'-deiodinase (5'-D) activity was investigated. Our results show that norepinephrine, an alpha- and beta-adrenergic agonist elicited an increase in thymus 5'-D activity. Isoproterenol, beta-adrenergic agonist, also increased the enzyme activity, being less effective than norepinephrine. Moreover, alpha-adrenergic agonists, i.e., methoxamine, an alpha1-agonist, and clonidine, an alpha2-agonist, did not increase 5'-D activity. The effect of isoproterenol was potentiated by methoxamine, but the potentiating effect was observed only at doses of isoproterenol which induce submaximal activation of the enzyme. Administration of propranolol, beta-adrenergic blocker, and prazosin, an alpha1-adrenergic blocker, inhibited significantly the activation of the enzyme induced by norepinephrine. However, yohimbine, an alpha2-adrenergic blocker, had small effect. These results show, in hypothyroid rats, a clear regulation by adrenergic mechanisms of 5'-D activity in the thymus, where alpha- and beta-adrenergic receptors might be involved.
Soutto
M
M
Department of Medical Biochemistry, The University of Seville School of Medicine, Spain.
Guerrero
J M
JM
Molinero
P
P
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D004357:Drug Synergism; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D007453:Iodide Peroxidase / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism*; D008297:Male; D008729:Methoxamine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects / Q000502:physiology*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology*; D013950:Thymus Gland / Q000187:drug effects / Q000201:enzymology* / Q000648:ultrastructure*
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D007527:Isoenzymes; D018340:Receptors, Adrenergic, alpha-1; D011943:Receptors, Adrenergic, beta; D007453:Iodide Peroxidase; D008729:Methoxamine; D009638:Norepinephrine