RESPIRATORY RESPONSE OF DIAZEPAM IN THE RABBIT

Experiments were carried out on bilaterally vagotomized rabbits under local anaesthesia.The effects ofdiazepam(2 mg/kg,i.v.)on respiration and cardiovas-cular activity were investigated.In the first group of animals which breathednaturally,intravenous administration of diazepam resulted in a reduction in respi-ratory minute volume,decrease in heart rate and arterial blood pressure.Inthe second group,experiments were performed on immobilized rabbits underpositive pressure artificial ventilation.Diazepam caused decreases in both theinspiratory and expiratory durations,thus shortening the respiratory cycle.Mean-while,the oscillatory frequency of high frequency oscillation(HFO)was increased,the amplitude of the phrenic nerve discharge was decreased,and the arterialblood pressure was also lowered.In the third group,when respiration of theanimals had been made either apneustic by decerebration at pontine level orgasping by transection at the medullary striae,diazepam also caused a reduction inthe amplitud f the phrenic nerve discharges,prolongation of the respiratorycycle and lowering of blood pressure.The results obtained indicate that diazepaminhibits the respiratory activity and lowers blood pressure.These effects are pos-sibly mediated mainly by the medulla oblongata.