PLASMA CONCENTRATIONS OF NORADRENALINE AND ADRENALINE AND PLASMA RENIN ACTIVITY DURING EXTRADURAL BLOCKADE IN DOGS

Anaesthetized dogs (pentobarbitone 25 mg kg^–1+ 3 mg kg^–1h^–1) with a Teflon catheter inserted to the femoral arteryfor pressure and heart rate measurement and blood sampling werestudied. Eitradural puncture was carried out at L7-S1 underx-ray control and 2% lignocaine (1 ml min^–1) infused forapproximately 10 min. During extradural block a decrease inarterial pressure was accompanied by a simultaneous decreasein plasma noradrenaline concentration (NA) and a compensatoryincrease in plasma renin activity (PRA), which became significant15 min after commencing the block when the arterial pressurewas at the minimum. Dihydroergotamine (DHE) led to a rapid reversalof the hypotension with no change in heart rate and a decreasein PRA. Hypovolaemia (blood loss 5 ml kg^–1) was inducedbefore and during block, respectively, in two further experimentalgroups. Increased NA and PRA were found under hypovolaemia withoutextradural block, but only PRA increased with hypovolaemia anda block. The effects of DHE in the later studies were comparableto those observed in the initial study.