EFFECT OF SODIUM-BICARBONATE ADMINISTRATION ON RENAL-FUNCTION OF HORSES

Objectives-To describe changes in renal function of horses after; oral and IV administration of sodium bicarbonate (NaHCO3) and to determine whether changes are dose dependent. Animals-6 Standardbred mares. Pro cedure-Blood and urine samples for determination of renal function wer e collected immediately before and at hourly intervals for 12 hours af ter administration of each of 3 oral doses (1,500, 1,000, and 250 mg/k g of body weight, in 3 L of water) and 1 IV dose (250 mg/kg, 5% soluti on) of NaHCO3, or water (3 L orally). Results-NaHCO3 induced increases in urine flow, electrolyte-free water reabsorption; urine concentrati ons of sodium and bicarbonate; fractional excretion of sodium, potassi um, chloride, and bicarbonate; urinary excretion and clearance of sodi um and bicarbonate; urine pH and anion gap; and mean plasma concentrat ion of antidiuretic hormone. NaHCO3 induced attenuation in reduction w ith time of urine excretion and clearance of potassium, chloride, and osmoles, and induced reduction in urine osmolality. Plasma aldosterone and atrial natriuretic peptide concentrations and glomerular filtrati on rate were not modified. Conclusions-Renal responses to NaHCO3 load emphasize conservation of plasma Volume and re-establishment of acid-b ase balance over control of hyperosmolality by means of diuresis, natr iuresis, and increased bicarbonaturia. These responses imply a large f luid shift from the extravascular space to the vascular compartment, w hich was eliminated via diuresis, thus preventing hypervolemia.