Heroin-Induced Alterations in Leukocyte Numbers and Apoptosis in the Rat Spleen1

The present study assessed the effects of acute heroin treatment on the cellularity of the rat spleen and the rate of splenocyte death by necrosis or apoptosis. The results showed that 1 h after a single injection of heroin, the total number of leukocytes in the spleen was decreased in a dose-dependent manner. Prior injection of naltrexone completely blocked heroinʹs effect, and the heroin-induced decrease in splenic leukocytes was not associated with a heroin-induced increase in circulating leukocytes. A 1-h exposure to heroin did not increase levels of lactate dehydrogenase, a cytosolic enzyme, in supernatants of splenic mononuclear cells cultured for 45 min or 24 h, suggesting that heroin does not increase necrotic death in the spleen. In contrast, a 1-h heroin treatment did increase the percentage of Annexin V+ cells in 0- and 24-h cultures of splenic mononuclear cells, indicating that heroin increases apoptotic death in the spleen. A 3-h exposure to heroin also produced a significant increase in apoptosis in the spleen. DNA fragmentation, a marker of cells in late stages of apoptosis, could not be detected in fresh splenocytes, but was evident in 24-h cultures of splenic mononuclear cells from saline- and heroin-treated rats. These results demonstrate that a single administration of heroin produces a decrease in the number of splenic leukocytes and an increase in the apoptotic death of splenic mononuclear cells.