Adrenalectomy modifies the effect of intracerebral histamine on the cold-stimulated TSH secretion in male rats.

Cold-stimulated TSH secretion remained normal after adrenalectomy in conscious male Sprague-Dawley rats, but the inhibitory effect of a small dose of histamine (1.0 micrograms/rat into the 3rd ventricle, i.c.v.) on the TSH secretion was abolished. Adrenaline (0.01-1.0 mg/kg s.c.) inhibited dose-dependently the cold-stimulated TSH secretion. However, although adrenalectomy causes a prominent decrease in releasable adrenaline, a larger dose of histamine (2.5 micrograms/rat i.c.v.) decreased the TSH secretion. The effect of histamine was not modified after pretreatment with either corticosterone or dexamethasone, irrespective of whether intact or adrenalectomized rats were studied. Corticosterone decreased and dexamethasone increased the cold-stimulated TSH secretion when given intraperitoneally. Chlorisondamine (10 mg/kg i.p.), a peripheral ganglionic blocking drug, suppressed the TSH cold-response in intact rats. Histamine (1.0 microgram/rat i.c.v.) had no additional inhibitory effect after chlorisondamine. The results suggest that the effect of intracerebral histamine on cold-stimulated TSH secretion is caused neither by stimulation of the hypothalamus-pituitary-adrenocortical axis nor by increased adrenomedullary catecholamine release. Further, the effect of intracerebral histamine is obviously not due to enhanced neurosympathetic activity. The effect of histamine is modified by adrenalectomy, but the adrenal glands are not essential for it.