Objective: To study the effects of intracerebroventricular injection of histamine, its H1 and H2 antagonists on body temperature in rabbits.
Design: Experimental study.
Animals: Thirty male New Zealand White rabbits weighing 2.5 - 3 kg.
Procedure: Implantation of a stainless steel guide cannula into the lateral cerebral ventricule , intracerebroventricular injections of histamine (25, 50 and 100 g/rabbit), prometazine (150 g/rabbit), ranitidine (150 g/rabbit) and normal saline (as control) with a 25 p1 Hamilton syringe, measurement of rectal temperature at 15, 30, 45, 60, 75 and 90 minutes past - injection by a digital thermometer. Statistical analysis: Repeated measures one way ANOVA. Duncan’s Measures Relnge test, peireel “t” test.
Results: ICV injection of histamine at dose rates of 50 and 75p g/rabbit decreased the rectal temperature for 30 and 60 minutes post - injection, respectively. Promethazine (150 g/rabbit) had no effect, whereas ranitidine (150 g/ rabbit) increased rectal temperature for 30 minutes post - injection. In addition, pretreatment with promethazine didn’t inhibit the hypothermic effect of histamine but pretreatment with ranitidinc prevented this effect.
Clinical implication: From the results it is concluded that the activation of brain histaminergic system produces a hypothermic effect which is mediated through its central H2 but not H1 receptors in rabbits.
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