Attempts to antagonize the effect of histamine on the cold-stimulated thyrotropin secretion in male rats.
Histamine given directly into the 3rd ventricle inhibits the enhancement of thyrotropin secretion induced by cold-exposure (4 degrees, 30 min.) in male rats. This effect was antagonized neither by mepyramine, a H1-receptor antagonist, nor by cimetidine, a H2-receptor antagonist. Histamine would not have an indirect mechanism of action through adrenergic alpha 1- or alpha 2-receptors in rat hypothalamus, since pretreatment with neither phenoxybenzamine nor yohimbine had any effect on histamine suppressed TSH cold-response. Further, it was also tested if histamine could decrease the TSH secretion through cholinergic-, GABA-, serotonergic- or dopaminergic receptors but no results supporting such a mechanism of action were obtained. The effect of histamine was not modified by pretreatment with naloxone or desipramine either. Imidazole acetic acid, IAA, a metabolite of histamine, had no effect on cold-induced TSH secretion. It is concluded that the effect of exogenous histamine on cold-stimulated TSH secretion is not mediated through H1- or H2-receptors. Histamine may decrease brain noradrenergic activity which is important in the generation of TSH cold-response. In addition, the effect of exogenous histamine might be due to decreased endogenous histaminergic activity in rat brain.
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D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D003080:Cold Temperature; D003891:Desipramine / Q000494:pharmacology; D018492:Dopamine Antagonists; D018756:GABA Antagonists; D006632:Histamine / Q000494:pharmacology*; D006633:Histamine Antagonists / Q000494:pharmacology*; D007276:Injections, Intraventricular; D007461:Iodoacetates / Q000494:pharmacology; D019807:Iodoacetic Acid; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D010276:Parasympatholytics / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013238:Stereotaxic Techniques; D013312:Stress, Physiological / Q000378:metabolism; D013972:Thyrotropin / Q000378:metabolism*
D000317:Adrenergic alpha-Antagonists; D018492:Dopamine Antagonists; D018756:GABA Antagonists; D006633:Histamine Antagonists; D007461:Iodoacetates; D010276:Parasympatholytics; D009270:Naloxone; D006632:Histamine; D013972:Thyrotropin; D003891:Desipramine; D019807:Iodoacetic Acid