Effect of prednisolone on amino acid-induced changes in renal haemodynamics and tubular function

The effect of oral prednisolone treatment on renal haemodynamics, tubular function and various hormones during amino acid infusion was studied in 14 normal men. A balanced amino acid solution was infused for 120 min, before and after 4 days of prednisolone treatment (40 mg day-1). During amino acid infusion before prednisolone glomerular filtration rate, renal plasma flow, urinary sodium excretion, fractional excretion of sodium, lithium clearance, fractional excretion of lithium, serum insulin (s-insulin), plasma glucagon (p-glucagon) and s-growth hormone increased, whereas p-atrial natriuretic peptide, p-aldosterone, p-vasopressin and s-insulin-like growth factor 1 were unchanged, and potassium excretion and fractional excretion of potassium fell. After prednisolone treatment the most important differences during amino acid infusion were a significantly lower fractional excretion of sodium after 120 min (before prednisolone 26%; after prednisolone-7%; p < 0.05), a more pronounced increase in s-insulin after 120 min (before 118%; after 200%; p < 0.05) and a lower s-potassium. In conclusion, amino acid infusion increased fractional sodium excretion in healthy men, and this increase was reduced by prednisolone due to increased reabsorption in the distal tubules. It is suggested that the more pronounced the increases in plasma insulin and the decrease in serum potassium are mediators of the increased distal tubular sodium reabsorption during amino acid infusion during prednisolone treatment.