Catecholaminergic Regulation of TSH and Growth Hormone Release in Ovariectomized and Ovariectomized, Steroid-Primed Rats

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Abstract
Third ventricular injection of dopamine (DA), Piribedil (ET-495), a DA receptor stimulator, norepinephrine (NE), epinephrine (E) and systemic administration of larger doses of DA and the receptor stimulant, apomorphine (APM), were used to evaluate their role in the regulation of TSH and GH secretion in ovariectomized (OVX) as well as ovariectomized, estrogen-progesterone treated (OEP) rats. Intraventricular or i.p. injection of DA or its agonists, ET-495 and APM, caused a lowering of plasma TSH and an elevation of plasma GH concentration in OVX as well as in OEP rats. In contrast, intraventricular injection of NE or E increased plasma TSH and GH concentration. On the basis of these results it is concluded that the central dopaminergic system is inhibitory to TSH secretion, as reflected in our experiments by the significant reduction of TSH levels. On the other hand, the noradrenergic and adrenergic system has a stimulatory role on the release of TRH as evidenced by the increase in plasma TSH levels. Activation of dopaminergic, noradrenergic and adrenergic systems appears to promote release of hypothalamic GH releasing hormone as reflected in the enhanced concentration of plasma GH, but the precise physiological role of these biogenic amines in modulating the release of TSH and GH hormone remains to be elucidated.