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Analysis of depressant effect of diazepam on the amplitude of phrenic nerve discharge in rabbits

Zheng wenan, Xu Ningshan, Zhang Jingru

Department of Physiology, Shanghai First Medical College. Shanghai, China

Abstract

Our previous study indicated that in awake rabbits diazepam depressed the amplitude of phrenic nerve discharge, increased respiratory rate, shortened both the inspiratory and expiratory durations (T_(I) and T_(E)) and lowered arterial blood pressure. In the present experiments, the effects of some drugs on the,above-mentioned diazepam actions were further examined in 35 rabbits. GABA caused depression of the amplitude of phrenic discharge and blood pressure, an effect similar to that of diazepam. But, different from diazepam, GABA prolonged both T_(I) and T_(E), and thus decreased the respiratory rate. Pretreatment of either isoniazid, an amino acid decarboxylase inhibitor, or GABA receptor antagonist picrotoxin prevented the depressant effect of diazepam on the amplitude of phrenic discharge. However, the shortening of T_(I) and T_(W) by diazepam was not affected in pretreatment of picrotoxin. When given alone, diazepam produced a fall on blood pressure lasting for more than one hour. In isoniazid or picrotoxin pretreated rabbits, however, diazepam exhibited a transient depressor effect lasting only 2 to 10 minutes. Neither naloxone (an opiate receptor antagonist) or cyproheptadine (a serotonin receptor antagonist) pretreatment affected the depressant effects of diazepam upon the amplitude of phrenic discharge and blood pressure. The results obtained suggest that the depressant effect of diazepam on the amplitude of phrenic discharge is mediated by GABA, while endorphins and serotonin seem not to be involved. Prolongation of the depressor effect of diazepam is possibly attributable to the participation of GABA, since following block of GABA synthesis or GABA receptors diazepam lowered blood pressure only transiently.

Key words: Diazepam;GABA;Isoniazid;Picrotoxin;Naloxone;Cyproheptadine;Phrenic discharge;Blood pressure

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Citing This Article：

Zheng wenan, Xu Ningshan, Zhang Jingru. Analysis of depressant effect of diazepam on the amplitude of phrenic nerve discharge in rabbits. Acta Physiol Sin 1985; 37 (2): (in Chinese with English abstract).