The behavioural, cardiovascular and respiratory actions of morphine-N-oxide in the dog

A comparison between the actions of morphine and morphine- N-oxide (MNO) on behaviour, blood pressure, heart rate and respiration of both conscious and anaesthetised dogs has been studied. In the conscious dog morphine was more potent than MNO in producing sedation when both drugs were given subcutaneously. MNO had no antimorphine activity. Intravenously administered morphine or MNO caused sham rage, tachycardia and an increased respiratory rate in the conscious dog. Morphine was more potent than MNO in producing these actions. The effects of these drugs on the blood pressure of conscious dogs varied; all doses of morphine caused pressor response, whereas small doses of MNO produced pressor responses while larger doses cause depressor responses. In the anaesthetised dog intravenous injections of morphine or MNO produced biphasic depressor responses, bradycardia and decreased respiratory rate. Any difference in activity between these drugs may be due to morphine having a greater ease of entry into the brain than MNO.