Chemical characterization and regulation of endogenous morphine and codeine in the rat.

Data on the tissue distribution of morphine and codeine in rat are presented. The concentration of these two opiate alkaloids seems to be distributed uniformly in the cortex, midbrain, pons/medulla and cerebellum. The spinal cord and the adrenal gland have high levels of morphine and codeine and the adrenal has more codeine than morphine. The major fraction of the alkaloids reside in a synaptosomal fraction and are present in tissues as the sulfate conjugate. The levels of morphine in the spinal cord and the urinary excretion of morphine are elevated in the arthritic rat model. We used extracted alkaloid samples from arthritic rats spinal cord for analysis by mass spectrometry and found molecular ions identical with morphine and codeine. The results are discussed in the light of possible physiological roles of endogenous morphine and codeine.