title: Effects of thyroid hormone deficiency on pre- and postsynaptic noradrenergic mechanisms in the rat cerebral cortex.
abstract: Thyroid hormones are known to influence the noradrenergic neurotransmission in several peripheral organs. In order to find out whether similar changes exist in the central nervous system, we investigated adrenoceptor-mediated responses in the rat brain cortex during propylthiouracil-induced hypothyroidism. In contrast to unchanged basal cAMP levels, the cAMP accumulation following (-)noradrenaline incubation (3 X 10(-6)--3 X 10(-5) M) was significantly reduced in brain slices from hypothyroid animals. The difference between controls and propylthiouracil-fed rats became more pronounced when (-) isoprenaline (3 X 10(-6)--3 X 10(-5) M) was used for selective stimulation of beta-adrenoceptors. Since the cAMP increase mediated via alpha-adrenoceptors was not affected, it may be concluded that thyroid hormone deficiency only impairs the beta-adrenergic transmission. Phosphodiesterase activity remained unaltered suggesting that thyroid hormones influence the beta-adrenoceptors or the adenylate cyclase coupled to it. The sensitivity of presynaptic alpha-adrenoceptors modulating the release of noradrenaline was evaluated using occipital cortical slices preincubated in 3H-noradrenaline. Clonidine inhibited whereas phentolamine enhanced the 3H-overflow induced by electrical stimulation in a dose-dependent manner. No differences could be detected between control- and propylthiouracil-treated animals. Thus presynaptic alpha-adrenoceptors are not affected by hypothyroidism.
mesh_terms: D000818:Animals; D002540:Cerebral Cortex / Q000201:enzymology / Q000378:metabolism*; D003000:Clonidine / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D007037:Hypothyroidism / Q000139:chemically induced / Q000378:metabolism*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D011441:Propylthiouracil; D051381:Rats; D011941:Receptors, Adrenergic / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*
chemical_list: D011941:Receptors, Adrenergic; D011943:Receptors, Adrenergic, beta; D011441:Propylthiouracil; D000242:Cyclic AMP; D010727:Phosphoric Diester Hydrolases; D007545:Isoproterenol; D003000:Clonidine; D009638:Norepinephrine; D010646:Phentolamine