The effects of acute and chronic administration of morphine on the turnover of brain and adrenal catecholamines in rats.

Brain and adrenal catecholamine turnover in adult female rats treated with morphine was investigated. A different time course response of brain and adrenal catecholamines to alpha-methyl-p-tyrosine methyl-ester (AMT) administration in normal rats was observed; the catecholamine turnover rate in adrenal glands appeared to be much slower than in the brain. Acute morphine increased the turnover of brain dopamine and noradrenaline as well as of adrenal catecholamines, whereas chronic morphine treatment induced a decrease in the turnover of brain noradrenaline. Withdrawal induced by nalorphine produced an increase in the utilization of brain noradrenaline and adrenal catecholamines; this effect could be related to the withdrawl stress situation induced by the opiate antagonist. Although the mechanism of morphine action may implicate other neurotransmitters besides catecholamines, our results contribute to evidence that brain and adrenal catecholamines could be involved in the mechanism of morphine tolerance and/or dependence.