The effect of morphine upon CSF opioids in dogs

Cerebrospinal fluid opioid activity was measured in dogs before and after morphine administration in order to investigate whether morphine results in an increase in CSF endogenous opioid levels. CSF was fractionated on a gel filtration column, and these fractions were assayed using a radioreceptor assay. Several peaks of opioid activity were seen in dog CSF both before and after morphine treatment. The predominant change in opioid peak patterns was the appearance after morphine treatment of a large peak in the elution position of morphine itself. Radiotracer studies verified that micromolar concentrations of morphine were present in CSF, which is enough morphine for potent binding activity. In addition to the increased activity in the elution position of morphine, several peaks of endogenous opioid activity showed increases after morphine treatment which were statistically significant.