Lack of Evidence for an Inhibitory Role Played by Tuberoinfundibular Dopaminergic Neurons on TSH Secretion in the Rat

Abstract

The role of dopamine (DA) in the control of thyroid stimulating hormone (TSH) secretion in basal or cold stimulated conditions was investigated by using pharmacological or neurosurgical tools. The intraventricular injection of DA (5 μg/animal) or the subcutaneus (s.c.) injection of a dopaminomimetic agent failed to induce changes of TSH plasma levels in normal or in cold stimulated conditions. The same results were obtained by intraperitoneal (i.p.) administration of haloperidol, a blocker of dopaminergic receptors. The complete deafferentation of hypothalamus, which causes degeneration of norepinephrinergic nerve endings and leaves the DA tuberoinfundibular system unaffected, prevented the TSH release evoked by cold exposure. α-Methyl-p-tyrosine (α-MpT) (250 mg/kg i.p.), which causes a remarkable reduction of DA in the median eminence (ME) of deafferented animals, was unable to restore the TSH response to cold. Collectively these results seem to suggest that DA does not play a significative role in the control of TSH secretion in the rat.

Studies on the Inhibitory Effect of Apomorphine and Bromocryptine on Basal and TRH Induced Level of TSH and PRL in Hypothyroid Rats under Pentobarbiturate Anesthesia

“…Moreover, also an increase of TSR level after a specific dopaminergic blocker sulpiride (Zanoboni et al, 1979) or after diethyldithiocarbamate (blocker of dopamine-beta-hydroxylase) which inhibits the conversion of dopamine to norepinephrine (Montoya et al, 1079;Männistö et al, 1979). However, the inhibitory role of dopaminergic neurons on TSR secretion in the rats was subjected to a criticism by Annunziato et al (1979) who failed to induce changes of TSH level in plasma either by intracerebroventricular injection of dopamine or by subcutaneous injection of bromocryptine (dopaminergic agonist) and intraperitoneal injection of haloperidol (dopaminergic antagonist).…”

Η Επιδραση Της Ντοπαμινης Στην Εκκριση Της TSH Σε Ασθενεις Με Χρονια Μη Θυρεοειδικα Νοσηματα

“…(Foord S.Μ., 1980). Μελέτη σε πο ντίκια για την απόδειξη της δράσης της ντοπαμίνης έδωσε αντίθετα αποτε λέσματα από τα παραπάνω,in vitro όμως " μελέτη σε απομονωμένα υποφυ σιακά κύτταρα (Annunziato L., 1979), επιβεβαιώνει την ανασταλτική επί δραση "της ντοπαμίνης στην TSH. (Metcalf G, 1981 (Roti Ε., 1978).…”