title: Presynaptic adrenoceptors on the regulation of tyrosine hydroxylase activation by potassium.
abstract: The role of the presynaptic alpha and beta-adrenoceptors on the regulation of tyrosine hydroxylase activity was studied in guinea pig atria depolarized with 50 mM K+. The presence of the beta-blocker propranolol (0.1 microM), alpha-blockers phentolamine (0.31 microM) or yohimbine (0.3 microM) or the alpha-agonist clonidine (0.1 microM) in the incubation medium did not affect tyrosine hydroxylase activation by 50 mM K+. On the contrary, the beta-agonist isoproterenol (0.012 microM) potentiated the activation produced by 50 mM K+, effect blocked by propranolol. Also the phosphodiesterase inhibitor, 1-methyl-3-isobutyl-xanthine (100 microM), facilitated tyrosine hydroxylase activation by potassium. Isoproterenol might exert its facilitatory effect through the stimulation of presynaptic beta-adrenoceptors, activation of adenyl cyclase and consequent increase of the intraneuronal concentration of cAMP. Noradrenaline synthesis in guinea pig atria depolarized by K+ seems to be unrelated to the stimulation of presynaptic adrenoceptors and also independent of the regulation of neurotransmitter release.
mesh_terms: D000818:Animals; D004789:Enzyme Activation; D005260:Female; D006168:Guinea Pigs; D006325:Heart Atria / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D009638:Norepinephrine / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology*; D011433:Propranolol / Q000494:pharmacology*; D011941:Receptors, Adrenergic / Q000378:metabolism*; D014316:Tritium / Q000378:metabolism; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
chemical_list: D011941:Receptors, Adrenergic; D014316:Tritium; D011433:Propranolol; D014446:Tyrosine 3-Monooxygenase; D007545:Isoproterenol; D011188:Potassium; D009638:Norepinephrine