Changes of endogenous morphine and codeine contents in the fasting rat.

The alteration of endogenous opiate alkaloids during fasting state was investigated in rats. The concentrations of morphine and codeine in the cortex, midbrain, pons plus medulla, cerebellum, adrenal gland and pancreas were measured using radioimmunoassay for the opiates following high pressure liquid chromatography. The morphine and codeine contents of fasting rats showed maximum elevated levels in cortex, pons plus medulla and pancreas after 2 days of fasting, but after 1 day in midbrain. The opiate content of the cerebellum showed a tendency for a continuous increase during the 4 days. Adrenal glands of fasting rats had elevated levels at days 3 and 4, although there were great fluctuations within the groups.