Tubular secretion and effects of tienilic acid in the hen

The relationship between renal tubular secretion of the uricosuric diuretic tienilic acid (10 or 30 microgram/kg per min) and its saluretic effects was determined using a modified Sperber technique. A true tubular excretion fraction (TTEF) or 29.9 +/- 4.1% (mean +/- S.D.) was found for tienilic acid, a value significantly (P less than 0.001) reduced by novobiocin to 3.3 +/- 2.8%. This demonstrates active tubular secretion of the diuretic by an organic anion transport system in the hen kidney. Infusion of the diuretic into one leg vein caused a marked ipsilateral excess excretion of chloride, sodium and potassium; these effects were significantly reduced by novobiocin. Thus, in the hen a significant part of the saluretic effect of tienilic acid depends on the active secretion of the drug by tubular cells, as has previously been found for three loop diuretics i.e. ethacrynic acid, furosemide and piretanide. In analogy with these, it is suggested that the saluretic effect of tienilic acid is evoked mainly from the luminal side of the avian nephron. At an infusion rate of 20 microgram/kg per min of tienilic acid, a marked saluresis occurred; there was, however, no effect on the urinary urate excretion.