Opiates Stimulate Low Km GTPase in Brain

Abstract
Low Km GTP hydrolysis in rat brain is stimulated in a concentration‐dependent manner by the opiate alkaloid etorphine, and by the opioid peptide d‐Ala2‐leucine‐enkephalinamide. The opiate antagonist naloxone inhibits the maximal d‐Ala2‐leucine‐enkephalinamide stimulation of the GTPase, also with concentration dependency. The magnitude of maximally stimulated, opioid‐sensitive, GTP hydrolysis is differentially distributed across brain regions. Opioid‐stimulated GTPase may represent one means of identifying a specific type of opioid receptor.