The partial opiate receptor agonists, dezocine and ciramadol act as μ receptor antagonists at the feline ileocecal sphincter

The effects of two novel synthetic narcotic agonist/antagonists dezocine and ciramadol were examined at the ileocecal sphincter (ICS) in the intact anesthetized cat. Changes in blood pressure were seen with higher doses of both dezocine and ciramadol. No ICS pressure changes were seen in the ICS to dezocine and an increase in ICS pressure was seen only to the highest dose of ciramadol examined (10 mg/kg). The antagonist action of the two drugs were examined against submaximal doses of the μ receptor agonist morphine sulfate, ∂ receptor agonist methionine enkephalin and the k-receptor agonist dynorphin. Both drugs inhibit the ICS response to morphine sulfate. No inhibition of the responses to methionine enkephalin or dynorphin were seen with dezocine and only partial inhibition of the ICS response to dynorphin was seen with ciramadol.