The effect of selective noradrenergic denervation on thyrotropin secretion in the rat

The effect of DSP4 [N-(2-chloroethyl)-N-ethyl-2 bromobenzylamine], a neurotoxin which selectively lesions noradrenergic projections from the locus coeruleus, on thyrotropin (TSH) secretion was investigated in the rat. DSP4 treatment (60 mg/kg injected i.p. 10 days prior to experimentation) significantly decreased the noradrenaline (NA) content of the hippocampus, frontal cortex and hypothalamus of the rat brain. DSP4 treatment did not affect the clonidine (250 micrograms/kg, i.p ) or TSH-releasing-hormone (TRH 5 micrograms/kg i.v.) induced stimulation or the isoproterenol induced inhibition of TSH secretion in the rat. These results suggest that the noradrenergic projection from the locus coeruleus to the hypothalamus does not play a significant role in the regulation of TSH secretion. Furthermore, the noradrenergic deficiency did not give rise to the development of the abnormal TSH response to TRH administration which is frequently observed in depression.