In vivo hamster skeletal muscle preparation: morphine sensitive - naloxone insensitive

The hamster cheek pouch retractor muscle preparation has been evaluated as an assay model for morphine and the opiate antagonist, naloxone. The preparation is in vivo and stimulation of the muscle is reflex. The higher the concentration of morphine injected into the pouch the greater was the average percent reduction in contractile force. Unilateral injections of morphine did not affect the contralateral muscle and so action of the drug was judged to be peripheral and local. The results with naloxone suggested that the opiate receptors in this preparation were relatively insensitive to the drug. The model has potential as an in vivo assay system for testing opiates, opiate agonists and antagonists. It may also prove to be valuable in studying tolerance to opiates and the withdrawal syndrome, as well as serving as a model for pain modulation studies.