MORPHINE: DUAL EFFECTS ON PLASMA CATECHOLAMINES

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Abstract
Present studies demonstrate that morphine can increase, decrease, or not affect plasma catecholamines depending on the dose and on the experimental conditions under which it is given. In the conscious dog, morphine (30 mg s.c.) produces a marked elevation of plasma epinephrine but not norepinephrine. In contrast, morphine (15 mg i.v.) prevents the rise of both plasma epinephrine and norepinephrine in the anesthetized, laparotomized dog. Since neither dose of morphine changes plasma catecholamines significantly in the non-laparotomized, anesthetized dog, we suggest (a) that the catechol-lowering effect is due to the analgesic properties of morphine, and (b) that the catechol-raising effect is due to activation of separate central nervous system pathways which are suppressed by barbiturate anesthesia.