Chronic administration of morphine in cats: effects on adrenal and urinary catecholamines

Adrenaline and noradrenaline levels in the adrenal glands and the excretion of both bioamines in urine of adult cats were investigated after chronic administration of morphine and nalorphine-induced withdrawal. After 7 days of daily consecutive morphine treatment, a significant increase in the adrenal noradrenaline content and a drop in adrenaline content were observed. After 2 weeks of daily injection of morphine, no significant changes were observed in the adrenal catecholamine level. One month of treatment with the opioid caused a significant increase in the adrenal content of both adrenaline and noradrenaline. Urinary excretion of catecholamines was significantly increased during the 4 weeks of treatment. In animals subjected to spontaneous or induced withdrawal with nalorphine, the adrenal content of catecholamines was altered and the ratio adrenaline/noradrenaline in the adrenal gland was shifted towards noradrenaline. A first injection of morphine produced an excitant manic response characterized by hyperexcitement and aggressive behaviour; animals chronically treated with the drug showed a progressively diminished response to this effect of the drug. It is concluded that physical dependence on morphine is reached by cats chronically treated with morphine and that this effect of the drug influences adrenomedulllary function in a different fashion depending on the stage of morphine treatment.