COCAINE ADMINISTRATION INDUCES HUMAN SPLENIC CONSTRICTION AND ALTEREDHEMATOLOGIC PARAMETERS

Cocaine is a potent vasoconstrictor that has been shown to alter hemog lobin, hematocrit, and red blood cell counts in both animals and human s. The present study evaluated whether cocaine administration induces splenic constriction in men and whether spleen-volume changes temporal ly correlate with altered hematologic parameters. Spleen volume was as sessed at baseline and after cocaine administration (0.4 mg/kg) by usi ng magnetic resonance imaging. A group of five healthy men, aged 31 +/ - 2 (SE) yr and reporting occasional cocaine use (13 +/- 5 lifetime ex posures), participated. Cocaine reduced spleen volume by 20 +/- 4% (P < 0.03) 10 min after drug administration. Spleen volume returned to no rmal (101 +/- 3% baseline) within 35 min after cocaine administration, indicating that the reduction is a transient phenomenon. In subjects administered cocaine from whom blood samples were obtained (n = 3), co caine increased hemoglobin levels, hematocrit, and red blood cell coun t to 104.5 +/- 0.9, 105.6 +/- 1.2, and 106.5 +/- 1.0% of baseline leve ls, respectively (P < 0.03), but it did not alter white blood cell and platelet counts. Placebo administration (n = 5) did not alter hematol ogic parameters. These results suggest that cocaine induces splenic co nstriction in humans, and this may contribute to temporally concordant hematologic parameter changes. These events may help to preserve or i ncrease tissue oxygenation in periods of high oxygen demand and/or inc reased vascular resistance.