A COMPARISON BETWEEN THE HYPOTHERMIA INDUCED BY INTRAVENTRICULAR INJECTIONS OF THYROTROPIN RELEASING HORMONE, NORADRENALINE OR CALCIUM IONS IN UNANAESTHETIZED CATS

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Abstract
1 The hypothermia produced by intraventricular injections of thyrotropin releasing hormone (TRH) in unanaesthetized cats has been investigated. 2 TRH is more potent than either noradrenaline or calcium ions. It is estimated that the equi‐potent molar ratio for TRH: noradrenaline: calcium is 1:900:27,000. 3 TRH injections also produce profuse salivation, tachypnoea, cutaneous vasodilatation and frequently defaecation and vomiting. It is considered that the increased respiration is a major cause of the hypothermia. 4 Prior administration of phentolamine antagonized noradrenaline‐induced hypothermia but did not affect hypothermia produced by TRH or calcium ions. Pretreatment with α‐methyltyrosine did not affect the hypothermia induced by TRH, calcium ions or noradrenaline. 5 The calcium antagonists verapamil and xylocaine did not antagonize hypothermia induced by an injection of calcium ions. 6 The constituent amino acids of TRH did not produce hypothermia either individually or collectively. Thyroxine sodium produced a rise in temperature that was slow in onset, consistent with its known metabolic effects. TSH produced a small hypothermia unrelated to dose.