SOME EFFECTS OF MORPHINE ON RESPIRATION AND METABOLISM OF RATS

¹ Department of Pharmacology and Experimental Therapeutics, University of California, San Francisco Medical Center, San Francisco, California

A combined small animal body plethysmograph-metabolism chamber has been found useful for the study of the effects of morphine on respiration and oxygen consumption of rats. Relatively low doses of morphine (5-20 mg/kg) depressed tidal volume, respiratory rate, oxygen consumption and response to 10% CO₂. As the dose was increased (40-160 mg/kg) the stimulant effects of morphine antagonized some of the depressant effects but depression of respiratory rate persisted even at doses which produced tremors and convulsions.

Daily administration of 10 mg/kg of morphine resulted in development of tolerance to the depressant effects of a test dose of morphine on respiratory rate and oxygen consumption after 4 days and on response to CO2 after 8 days. However, some depression of tidal volume persisted for at least 12 days. No tolerance developed to the stimulant effects of morphine as evidenced by increases in minute volume and oxygen consumption following some of the test doses.

This article has been cited by other articles:

				G. Hilaire and B. Duron Maturation of the Mammalian Respiratory System Physiol Rev, April 1, 1999; 79(2): 325 - 360. [Abstract] [Full Text] [PDF]