Noradrenergic and dopaminergic modulation of thyrotropin secretion in the rat
Date
1987
Authors
Jaffer A.
Russell V.A.
Taljaard J.J.F.
Journal Title
Journal ISSN
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Publisher
Abstract
Noradrenergic and dopaminergic regulation of thyrotropin (TSH) secretion was investigated in adult male Wistar rats. TSH secretion displayed a circadian variation with peak serum TSH levels at 10.00 h. The α2-adrenoceptor agonist, clonidine (250 μg/kg, i.p.), was found to cause an enhancement of serum TSH levels at 10.00 h (160 ± 10% of control values, P < 0.001) which was antagonized by prior administration of the α2-adrenoceptor antagonist, yohimbine (3 mg/kg, i.p.). The α-adrenoceptor antagonist phentolamine caused a significant decrease in serum TSH levels at 10.00 h (62 ± 15% of control values, P < 0.05) at a dosage of 2 mg/kg, i.p. The α1-adrenoceptor agonist, phenylephrine (0.2 or 2 mg/kg, i.p.), was without effect as were the dopaminergic receptor agonist, apomorphine (1 or 5 mg/kg, i.p.), and the antagonist, sulpiride (20 mg/kg, i.p.). The β-adrenoceptor agonist, isoproterenol (1 mg/kg, i.p.) was found to cause a decrease in serum TSH levels at 10.00 h (70 ± 16% of control levels, P < 0.01), which was completely antagonized by prior administration of the β-adrenoceptor antagonist, propranolol (10 mg/kg, i.p.).TSH-releasing hormone (TRH, 5 μg/kg, i.v.) caused a significant stimulation of TSH secretion (470 ± 63% of basal levels, P < 0.001), which was not affected by prior treatment of the rats with yohimbine (0.1 mg/kg, i.p.), phentolamine (2 mg/kg, i.p.), propranolol (10 mg/kg, i.p.) or sulpiride (20 mg/kg, i.p.). There was, however, a tendency towards a decrease in the TRH-stimulated release of TSH in rats pretreated with phentolamine or propranolol. The results of this study clearly demonstrate the existence of stimulatory α2-adrenoceptors as well as inhibitory β-adrenoceptors which modulate TSH secretion in vivo and which can be used to test noradrenergic receptor responsiveness under different pharmacological conditions.
Description
Keywords
clonidine, isoprenaline, phentolamine, phenylephrine, propranolol, protirelin, sulpiride, thyrotropin, yohimbine, animal experiment, dose time effect relation, drug antagonism, drug comparison, drug efficacy, endocrine system, etiology, intraperitoneal drug administration, nonhuman, pharmacokinetics, priority journal, rat, Animal, Apomorphine, Circadian Rhythm, Dopamine, Male, Norepinephrine, Protirelin, Rats, Sulpiride, Support, Non-U.S. Gov't, Sympathomimetics, Thyrotropin
Citation
Brain Research
404
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404
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