Effect of chronic lead exposure on the canine bone marrow.

The effect of chronic oral led acetate administration on canine bone marrow was studied. Two dogs (group 1) were used as controls, 4 dogs (group 2) were given 2 mg of lead/kg of body weight daily, and 4 dogs (group 3) were given 5 mg of lead/kg daily. After a 7-day stabilizaion period, lead dosing was conducted for 91 days (13 weeks), after which half of each group was treated with calcium ethylenediaminetetraacetic acid. All dogs were then observed for another 28 days (4 weeks). Blood lead values and bone marrow cellular changes were monitored once a week during the 126 days (18 weeks) of study. Lead-dosed dogs had lower weight gains than the controls. Clinical signs of toxicosis were observed after 6 weeks in one dog in group 3. Anorexia, body weight loss, CNS depression, muscular weakness, and trembling were seen. Blood lead concentrations increased in all group 2 and 3 dogs. Lead caused increases in bone marrow segmented neutrophils and myeloid series cells, and increased myeloid:erythroid ratios. Blood lead concentrations and myeloid:erythroid ratios decreased after cessation of lead administration.