Effect of morphine on the clearance of endogenous creatinine and blood clinical chemicals in the rat.

The effect of morphine on urine and blood serum concentration of Na+, K+, Cl- and other chemicals was determined using Sprague Dawley rats, previously hydrated with 50 ml/kg of 0.5% NaCl to provoke an increased diuresis. Morphine caused about a 90% decrease in the urine concentration of Na+, K+ and Cl-. This reduction in the urine electrolyte excretion was associated with a small but significant increase in the concentration of the blood Na+ and Cl-. The antidiuresis and the decrease in urine electrolytes caused by morphine was paralleled by a 50% reduction of the endogenous creatinine clearance. An acute dose of 7.5 mg/kg morphine i.p. did not alter the concentration of 13 other clinical blood chemicals with the exception of urea. However, after 18 hr of morphine pellet implantation, a significant increase was found in the blood urea and in the activity of serum transaminases. Lactic dehydrogenases isoenzymes one and two were significantly increased in the blood of rats chronically administered with morphine.