Circulating leucocytic changes to catecholamines in rats

Intradermal injection of 5 to 10 μg norepinephrine or coli endotoxin was followed 1 to 5 hours later by neutrophilia and lymphopenia in the rat. Administration of a monoamine oxidase inhibitor (tranylcypromine) or of desmethylimipramine, which interferes with the catecholamine-inactivating process, potentiated the neutrophilia producing effect of norepinephrine. Histamine did not produce any changes in the differential leucocyte count when given alone, but did inhibit the neutrophilia normally resulting from norepinephrine treatment. The role of norepinephrine in the delayed phase of the acute inflammatory process is discussed.