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

Use of diuretics in the neonatal period

The use of diuretics is extremely frequent in sick neonates, the more so in very premature newborn infants. The use of diuretics in patients whose kidney function is immature necessitates a thorough knowledge of renal developmental physiology and pathophysiology. This review presents the basic aspects of body fluid homeostasis in the neonate, discusses the development of kidney function, and describes the mechanisms involved in electrolyte and water reabsorption along the nephron. Diuretics are then classified according to the site of their action on sodium reabsorption. The use of diuretics in sodium-retaining states, in oliguric states, in electrolyte disorders, and in arterial hypertension, as well as in a few specific disorders, is presented. Common and specific adverse effects are discussed. Recommended dosages for the main diuretics used in the neonatal period are given. New developments in diuretic therapy are briefly mentioned.

Renal effects of adenosine A1-receptor blockade with 8-cyclopentyl-1,3-dipropylxanthine in hypoxemic newborn rabbits

The key role of intrarenal adenosine in mediating the hypoxemic acute renal insufficiency in newborn rabbits has been well demonstrated using the nonspecific adenosine antagonist theophylline. The present study was designed to define the role of adenosine A1 receptors during systemic hypoxemia by using the specific A1-receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). Renal function parameters were assessed in 31 anesthetized and mechanically ventilated newborn rabbits. In normoxia, DPCPX infusion induced a significant increase in diuresis (+44%) and GFR (+19%), despite a significant decrease in renal blood flow (RBF) (-22%) and an increase in renal vascular resistance (RVR) (+37%). In hypoxemic conditions, diuresis (-19%), GFR (-26%), and RBF (-35%) were decreased, whereas RVR increased (+33%). DPCPX administration hindered the hypoxemia-induced decrease in GFR and diuresis. However, RBF was still significantly decreased (-27%), whereas RVR increased (+22%). In all groups, the filtration fraction increased significantly. The overall results support the hypothesis that, in physiologic conditions, intrarenal adenosine plays a key role in regulating glomerular filtration in the neonatal period through preferential A1-mediated afferent vasoconstriction. During a hypoxemic stress, the A1-specific antagonist DPCPX only partially prevented the hypoxemia-induced changes, as illustrated by the elevated RVR and drop in RBF. These findings imply that the contribution of intrarenal adenosine to the acute adverse effects of hypoxemia might not be solely mediated via the A1 receptor.

Increased renal angiopoietin-1 expression in folic acid-induced nephrotoxicity in mice

Growth factors affect epithelial regeneration after acute renal injury, but less is known regarding the expression of vascular growth factors in this setting. A mouse model of folic acid (FA)-induced nephrotoxicity was used to study the expression of angiopoietins (Ang), factors that bind the Tie-2 receptor and modulate endothelial growth. Tubular damage was detected 1 d after FA administration; in the next 14 d, most tubules regenerated but patchy atrophy, with interstitial fibrosis, was also observed. Ang-1 immunostaining was detected between cortical tubules and in the vasa rectae of vehicle-treated animals. FA-induced nephropathy was associated with the acquisition of Ang-1 immunostaining in renal arterial walls and in a subset of injured cortical tubules that failed to stain with periodic acid-Schiff stain, which indicated that they were distal tubules. Renal Ang-1 protein levels were significantly increased after FA administration, compared with time-matched control values, as assessed by Western blotting. Capillaries between regenerating tubules expressed both Tie-2 and platelet-endothelial cell adhesion molecule. A subset of these endothelia expressed proliferating cell nuclear antigen, whereas capillary proliferation was absent in control samples. Therefore, FA-induced nephropathy is associated with increased Ang-1 protein expression in renal epithelia and arteries. In addition, Tie-2-expressing capillaries near damaged cortical tubules undergo proliferation. Further experiments are required to establish whether these events are functionally related.