Furosemide-induced electrolyte depletion associated with echinocytosis in horses.

Echinocytes have been incriminated in the pathogenesis of exertional diseases in horses. To evaluate the hypothesis that echinocytes are dehydrated erythrocytes, we decreased blood sodium and potassium concentrations in 4 horses by administering furosemide (1.0 mg/kg of body weight, q 12 h) for 2 days and we monitored CBC, serum and erythrocyte sodium and potassium concentrations, and echinocyte numbers. Serum sodium concentration decreased progressively over the 48 hours of furosemide administration, then returned to near baseline concentration at 168 hours. A statistically significant decrease (P < 0.05) in serum potassium concentration was observed at 24, 48, and 72 hours after initial furosemide administration, and remained less than the baseline value at the end of the study. Mean erythrocyte potassium concentration decreased rapidly and remained low at the end of the study. Minimal changes were observed in erythrocyte sodium concentration during the first 72 hours after furosemide administration, but the value was significantly (P < 0.05) increased at 168 hours. Type-I and type-II echinocyte numbers increased by 4 hours after furosemide administration and persisted throughout the study. Type-III echinocytes were not seen in baseline samples, but numbers increased only modestly after furosemide administration. Administration of epinephrine to well-hydrated horses increased echinocyte numbers only minimally, indicating that splenic contraction was not the likely cause for the furosemide-associated increase. To determine whether the decrease in erythrocyte potassium concentration and increase in sodium concentration was caused by furosemide acting directly on the erythrocyte membrane, we quantified erythrocyte potassium and sodium concentrations before and after incubation with furosemide in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)