Plasma thyrotrophin (TSH) response to intrahypothalamic injection of an alpha 2-adrenergic receptor agonist (clonidine)
Ishikawa, K.; Kakegawa, T.; Suzuki, M.
Acta Endocrinologica 111(1): 25-29
1986
ISSN/ISBN: 0001-5598 PMID: 2868601 Document Number: 281422
To delineate the site at which the central noradrenergic (NE) system may exert its stimulatory influence on the thyrotrophin (TSH) secretion, plasma TSH concentrations were measured before and after clonidine (an .alpha.2-agonist) administration to the hypothalamus of unanaesthetized, unrestrained rats. When the animals received a simultaneous injection of clonidine (0.2 .mu.g) and phenoxybenzamine (2.0 .mu.g) into the dorsomedial nucleus (DMN)/the paraventricular nucleus (PVN), a significant rise in TSH levels was observed. Injection of the mixture into the anterior hypothalamus, posterior hypothalamus, ventormedial hypothalamus, and arcuate nucleus had no influence on the plasma TSH concentration. Clonidine (10.0 .mu.g/100 g body weight) and phenoxybenzamine (100 .mu.g/100 g body weight) injected into the jugular vein also caused a prompt increase in the plasma TSH concentration. In rats with an intact small hypothalamic island, the TSH response to the iv injection of the drugs was considerably diminished. These data support the view that NE receptors in the DMN/PVN are of importance in exerting an NE-stimulatory influence on the TSH secretion, probably through the TRH neurons.