Neurotransmitter control of thyrotropin secretion in the rat.

In rats adapted to a +30 degrees C temperature for one week, transfer to a temperature of +4 degrees C increased immunoassay-able serum TSH from 150-300 ng/ml to 800-2000 ng/ml in 30 min. Since this response, as well as the level of serum TSH without stimulation, were decreased by reserpine, phentolamine, phenoxybenzamine, disulfiram and diethyldithiocarbamate, noradrenaline may be involved in the stimulation of TSH secretion. TRH-induced TSH increased was not blocked by reserpine. 1-Dopa, a noradrenaline precursor, decreased the TSH response to cold; alpha-methyl-p-tyrosine increased the TSH level. Apomorphine decreased the level of serum TSH and inhibited the response to cold. The possibility of a dopaminergic inhibitory factor released from the hypothalamus is discussed. 5-HT has possibly a role in the regulation of TSH secretion, since its precursor 5-HTP decreased the response to cold. No indication was found that acetylcholine is involved.