Neutrophilia-inducing activity in plasma of dogs recovering from drug-induced myelotoxicity

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Abstract
A search for factors in plasma which influence the blood neutrophil concentration of dogs is described. Following administration of vinblastine sulfate (VLB), the dog develops neutropenia due to destruction of mitotic cells in the bone marrow and then recovers. Infusion of normal dog plasma and of plasma from VLB-treated dogs taken immediately before or after the post-VLB neutropenic phase had no effect on the neutrophil concentration of normal dogs. However, post-VLB plasma induced neutrophilia in the recipient when taken 6-8 days after VLB, a time during which donor dogs were neutropenic. Plasma from neutropenic, HN2-treated dogs had a similar effect. The neutro-philia-inducing activity (NIA) of 6-day post-VLB plasma was found to be the consequence of an accelerated rate of release of neutrophils from the marrow. The NIA of 6-day post-VLB plasma was qualitatively dissimilar from that of endotoxin, cortisone, or epinephrine. Dogs rendered tolerant to the NIA of endotoxin were still responsive to the NIA of 6 days post-VLB plasma.