Skrzypczak W. F., K. Janus, Z. Muszczynski and D. Jankowiak: The effect of spironolactone (Aldactone) on electrolyte balance and renolfuncions of calves. Acta vet. Bmo, 63, 1994: 19-23. A short spironolactone test was carried out in a group of 10 clinically healthy calves at the age of 4 weeks. For 5 days (every 24 hours) the calves were administered Aldactone (Searle), per os, at a dose of 1 mglkg of body weight. Before the test began and 120 and 144 hours after giving the first spironolactone dose, the effective renal blood (ERBF) and plasma (ERPF) flow, and the glomerular filtration rate (GFR) were measured using sodium salt of p-aminohippuric acid and inulin. The levels of sodium, potassium and chlorides in plasma and erythrocytes were also determined. Some changes in the concentration of tested electrolytes were found in both the plasma and the intracellular fluid of erythrocytes. Changes in the renal function of calves were also indicated by an increase in effective renal plasma flow as well as by a decrease in glomerular filtration rate. Spironolactone, electrolyte b(llance, renal.fi!,nction, calves Calf kidneys are functionally efficient in the fIrst month oflife. However, they reveal some features of functional immaturity. These involve lowered effective renal blood (ERBF) and renal plasma (ERPF) flow,low glomerularfiltrationrate and low ability of urine concentration (Mercer etal.1978; Wanner etal.1981; Hartmann et al. 1987; Skrzypczak 1989; Skrzypczak etal. 1989; Skrzypczak 1991). The observed high tabular resorption ofNa, K and Cl in the frrst ~ days of life (Safwate et al., 1980; Skrzypczak, 1991) becomes lower as the age of calves increases (Safwate etal.1982; Skrzypczak 1989). The results of experiments show that, by the third day of life, mechanisms which control sodium resorption become active and kidney tubules respond to aldosterone infusion with the growth ofNa resorption (Safwate et al. 1980; Safwate et al. 1982; Itoh et al. 1985; Safwate 1985). Some authors, however, found a lack of correlation between the plasma renin activity and the aldosterone level, and sodium and potassium concentrations in the blood plasma (Siegler etal.1977; Moncaup etal.1980; Safwate etal.1982). Cabello (1980)evenreportsanegative correlation between plasma levels of aldosterone and sodium. Jankowiak (1989) showed that administering DOCA at a dose of 0.1 mglkg body weight Lm. caused a clearance drop and the urine excretion of sodium, potassium and chlorides also decreased. Safwate (1985) also noticed a lowering of sodium excretion in urine after aldosterone infusion, although he did not observe any changes in potassium excretion. Some authors indicate that there is a possibility of metabolic stimulation of the calf suprarenal glands in the first month of life (McEwan et al. 1968; Baranow-Baranowski etal. 1987). As can be seen from the literature review, there are many issues connected with tubular activity regulation in the postnatal period pertaining to electrolytes resorption which have not been fully explained yet (K a g a w a 1960; Bra u n Ii chand K e r s ten 1972; Cor v 0 I et al. 1981). The objective of this paper was to examine the effect of spironolactone (Aldactone) on electrolyte balance of body fluids and on glomerular filtration rate and effective blood and plasma flow through young calf kidneys. Materials and Methods The experiment was carried out on a group of 10 clinically healthy calves of cb. breed at the age of 4 weeks. They were kept in a calf-pen under constant, optimal conditions. Their left and right jugular vein had been catheterized and they had been weighed before the experiment began. Prior to the treatment period, the effective renal plasma (ERPF) and blood (ERBF) flow and the glomerular filtration rate (GFR) were defined. The levels of sodium, potassium and chlorides in blood plasma and erythrocytes were examined. To assess ERPF and GFR, sodium salt of p-aminohippuric acid (Serva-GmbH) and inulin (Sigma Chern. Co.) were used respectively. The clearance of these substances was measured using Bettge' s method. On the basis of ERPF and haematocrit, the amount of ERBF was defined and the filtration fraction (FF) was calculated. In order to block aldosterone activity, a short spironolactone test was conducted. The calves were administered 1 mglkg body weight of Aldactone (Searle) per os for 5 days. After 120 and 144 hours from giving the first dose of Aldactone, new examinations of ERPF, GFR values and Na, K and Cllevels in plasma and whole blood were carried out.