Neurotransmitter Control of Thyrotropin Secretion

Abstract

The central dopaminergic system seems to have an inhibitory influence on the secretion of thyrotropin (TSH) both in humans and rats. This is documented by observations that in humans, especially in subjects with primary hypothy-roidism, the dopamine precursor l-Dopa, dopamine receptor agonist bromocryptine, and dopamine itself decrease plasma levels of TSH and in some instances inhibit TSH secretory response to thyrotropin-releasing hormone (TRH). Conversely blockade of dopamine receptors leads to an elevation of circulating TSH. It is probable the dopaminergic drugs act on the pituitary thyrotrops rather than on the release of hypothalamic TRH. Analogous results were obtained in rats. In contrast, the noradrenergic system, studied mainly in rats, has a stimulatory influence on the secretion of TSH. This view is mainly supported by findings that acute interruption of noradrenergic neurotransmission causes a decrease of serum TSH levels and blocks the cold-induced stimulation of TSH secretion. The role of the central serotonergic system remains undecided because some experimental findings indicate that it has an inhibitory influence but others indicate an opposite function. The remaining transmitter systems have not been studied extensively enough to allow definite conclusions about their roles in the regulation of TSH secretion.

Hypothalamic thyrotropin-releasing hormone mRNA responses to hypothyroxinemia induced by sleep deprivation

“…Abundant evidence shows that dopamine acts on pituitary thyrotrophs (reviewed in Ref. 37). Recent evidence has also linked dopamine to the regulation of the expression of 5Ј-DII mRNA in the ARC-ME via a dopamine-and cAMP-regulated phosphoprotein found in tanycytes (28), which may be relevant insofar as 5Ј-DII mRNA was not found to be robustly increased in this region in the present study.…”

“…Although the PVN had not been explicitly quantitated in that study, the particularly low metabolic rates of adjacent structures indicate a decreased metabolic activity that may reflect tonic inhibition in this region. Another candidate factor, dopamine, exerts inhibitory control on TRH at two central levels, affecting both hypothalamic TRH release (4) and pituitary TSH responses to TRH (37). L-Dopa administration to hypothyroid patients lowers elevated TSH levels without changing the response to TRH (reviewed in Ref.…”

“…L-Dopa administration to hypothyroid patients lowers elevated TSH levels without changing the response to TRH (reviewed in Ref. 37). Abundant evidence shows that dopamine acts on pituitary thyrotrophs (reviewed in Ref.…”

TSH neurosecretory dysfunction (TSH-nd) in Down syndrome (DS): low risk of progression to Hashimoto's thyroiditis

“…Therefore, dysfunctions of the Hypothalamic-Pituitary-Thyroid axis in patients with DS may be associated with primary thyroid diseases or with disorders of TSH secretion dependent on insufficient dopaminergic control of pituitary secretion (19).…”

“…These findings are common in individuals with DS who are over 40 years old, and occur as dementia similar to Alzheimer's disease. Just like the substantia nigra and the ventral tegmental area (important dopamine-producing areas in the brain), the arcuate nuclei of the hypothalamus (dopamine producers that act as inhibitory hormone upon TSH secretion) could also be compromised (19)(20)(21).…”