Failure of the loop diuretic torasemide to improve renal function of hypoxemic vasomotor nephropathy in the newborn rabbit

The use of diuretic therapy in vasomotor nephropathy is a controversial top ic. It is generally agreed that diuretics in this situation enhance urinary output, reduce the degree of volume expansion, and improve cardiac and esp ecially the compromised lung function. It is less clear whether diuretic th erapy improves kidney function. The present study evaluates the effects of intravenous torasemide on renal function in 25 anesthetized ventilated hypo xemic newborn New Zealand White rabbits with vasomotor nephropathy. This we ll-established animal model mimics the renal physiology of the human newbor n and, in particular, that of the premature infant. Three groups of hypoxem ic rabbits were studied. The animals of group 1 (n = 8) received no diureti c therapy (hypoxemic control), and those of group 2 (n = 9) mere given a si ngle intravenous dose of torasemide (1 mg/kg) in a curative fashion 2 h aft er hypoxemia was induced. In the third group of animals (n = 8), torasemide was gh en preventively; a bolus intravenous dose of torasemide (0.2 mg/kg) was given before the induction of hypoxemia and sustained by the addition of 0.2 mg.kg(-1).h(-1) of the drug to the continuous intravenous infusion g iven throughout the entire 3-h hypoxemic period. Hypoxemia alone (group 1) caused acute renal insufficiency with a significant fall in mean arterial b lood pressure, GFR, and renal blood flow; the renal vascular resistance inc reased, and the filtration fraction was unchanged. The curative dose of tor asemide (group 2) induced a significant diuresis and natriuresis with minim al augmentation of urinary potassium excretion, converting mildly oliguric to nonoliguric acute renal insufficiency. In this group of animals, torasem ide did not improve the glomerular dysfunction. The preventive dose of tora semide (group 3) even somewhat worsened the already impaired tend functions without further increasing the diuretic effect of the drug. We conclude th at in hypoxemic newborn animals with renal dysfunction, torasemide is an ef fective potassium-sparing diuretic that unfortunately does not improve rena l blood flow and GFR, The failure of torasemide to attenuate the glomerular dysfunction of hypoxemic vasomotor nephropathy in the newborn rabbit is di sturbing. These data certainly caution against the overzealous use of loop diuretics in hypoxemic oliguric neonates.