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 A 1 receptors during systemic hypoxemia by using the specific A 1 -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 (ϩ44%) and GFR (ϩ19%), despite a significant decrease in renal blood flow (RBF) (Ϫ22%) and an increase in renal vascular resistance (RVR) (ϩ37%). In hypoxemic conditions, diuresis (Ϫ19%), GFR (Ϫ26%), and RBF (Ϫ35%) were decreased, whereas RVR increased (ϩ33%). DPCPX administration hindered the hypoxemia-induced decrease in GFR and diuresis. However, RBF was still significantly decreased (Ϫ27%), whereas RVR increased (ϩ22%). 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 A 1 -mediated afferent vasoconstriction. During a hypoxemic stress, the A 1 -specific antagonist DPCPX only partially prevented the hypoxemiainduced 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 A 1 receptor. Adenosine is ubiquitous in the kidney. Intrarenal adenosine vasoconstricts the preglomerular vessels via the A 1 receptors, while dilating the efferent arterioles via the A 2 receptors. It thus affects GFR as well as RBF and its distribution within the kidney. In addition to its vascular actions, intrarenal adenosine modulates renal mechanisms, including TGF, renin release, and the tubular handling of electrolytes and water. Intrarenal adenosine also appears to be an important hemodynamic mediator in some models of vasomotor nephropathy, such as those induced by intramuscular glycerol injection (1), contrast media (2), cisplatin (3), or hypoxemia (4).In animal models as in humans, hypoxemia can lead to functional renal insufficiency (5-7). In the newborn rabbit, acute normocapnic hypoxemia induces renal hypoperfusion with decreased GFR and RBF (4, 7-9). The underlying mechanism of this hypoxemia-induced vasomotor nephropathy still remains controversial. The chemoreceptor-mediated reflex and/or the activation of vasoactive factors such as angiotensin II (AII) (9), endothelin (10), nitric oxide (8), or bradykinin (11) have been suggested to play a role.We previously demonstrated that the administration of theophylline, a nonspecific antagonist to adenosine receptors, ameliorates the hypoxemia-induced renal hemodynamic changes seen in the newborn rabbit model (4). Moreover, in neonates with respiratory distress syndrome (12)
The purpose of this study was to establish the effects of intravenous dimethyl sulfoxide (DMSO), a solvent used in a wide variety of products (medicines), on kidney function in the newborn rabbit. Three groups of anesthetized, ventilated, normoxemic 4- to 8-day-old New Zealand White rabbits received a 90-min intravenous infusion of DMSO at a dose of 1.11 (group 1), 16.5 (group 2) or 111 μg/ kg/h (group 3). The only change observed in the animals of group 1 was a significant increase in filtration fraction (FF; p < 0.001), whereas no change at all was observed in the renal functional parameters of the animals of group 2. The highest dose of DMSO (group 3), however, caused a very significant (p < 0.001) decrease in renal blood flow (RBF) and a rise in renal vascular resistance (RVR), FF and urine volume (UV). Glomerular filtration rate (GFR) and systemic parameters such as pH, mean arterial blood pressure and heart rate did not change. The rise in GFR, RVR, UV (group 3 vs. 2) and FF (groups 3 vs. 2 and 2 vs. 1) was dose-dependent. No significant dose-dependent decrease in RBF was found. To the best of our knowledge, there are no previous reports on the effect of DMSO on renal function in the solvent doses used in this study. We ascribe the reported effects to the ‘immaturity’ of the newborn rabbit kidney. Consequently, this agent should be used with great caution in developmental studies.
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