Cerebral blood flow and tissue pO2 changes following local met-enkephalin administration in awake, freely moving cats

The effect of locally administered methionine-enkephalin on cerebrocortical blood flow and tissue pO2 was tested in chronic, awake, freely moving cats. Local cortical blood flow was measured with the H2-gas clearance method, and cortical pO2 in the same area was monitored with a polarographic technique using double Pt electrodes. Met-enkephalin was administered with a micropipette technique in 0.1, 0.5, 1.0 and 5.0 mumol/l concentrations in 20 microliters volume. Met-enkephalin caused a marked, dose dependent decrease of the cortical flow as well as of the cortical pO2. Following 5.0 mumol/l met-enkephalin the flow decreased more (x = 30.6%) than did the pO2 (x = 18%). The maximum effect could be observed 2-7 min following administration of the peptide, the duration of the effect was about 20 min. The threshold dose was found around 5-7 X 10(-8) M/l. Met-enkephalin in the above mentioned doses caused no vegetative, motor or behavioural changes in these experiments.