Nitrogen-Induced Bradycardia in Anesthetized Rats

Abstract

In order to differentiate the overall effect of pressure and the type and partial pressure of the component gases of the gas mixture 10 anasthetized, male Wistar rats average weight 400 g. and aged 6 months were exposed to 4 conditions of gas pressure and composition in a pressure chamber for periods of 2 hours on separate occasions. Heart rate, ECG, respiration, rectal temperature, chamber pressure and temperature, O2 and CO2 partial pressures were measured continuously. Both the character and time of onset of the developed bradycardia in the 4.2 ata condition differed from the other conditions. Manipulation of the composition of the gaseous environment at the point of the maximally developed bradycardia while keeping the overall pressure constant always produced a sustained tachycardia. Pharmacological interventions with vagus blocking (atropline) and a beta blocking drug propranalol were also studied.