Neonatal ACE inhibition in rats interferes with lung development.

The renin-angiotensin system (RAS) is developmentally up-regulated and it is essential for kidney development in several species. Given the fact that the rat lung undergoes postnatal development, the mammalian lung possesses the highest angiotensin-converting enzyme (ACE) levels and ACE activity increases during the first weeks postpartum, we tested the hypothesis that ACE inhibition influences postnatal lung development. Rats were given the ACE inhibitor enalapril (10 mg kg-1) from 0 to 9 days of age and their lungs were examined at day 4 and 9. Lung structure was evaluated by means of light microscopy, and surface tension of bronchoalveolar lavage fluid was measured by means of a Wilhelmy balance. Neonatal ACE inhibition lowered the surface tension of bronchoalveolar lavage fluid and caused widening of respiratory airspaces and thinning of alveolar septa. Our results suggest that early postnatal ACE inhibition in rats interferes with lung development

The renin-angiotensin system in renal tubulogenesis. Experimental studies in the rat

The kidney and the renin-angiotensin system (RAS) are vital regulators of blood pressure and salt-water balance. In order to appropriately regulate circulatory homeostasis, the kidney must undergo normal development, in which the RAS plays a crucial role. The main effector peptide of the RAS is angiotensin II (ANG II), which governs mammalian nephrogenesis predominantly through stimulation of ANG II type 1 (AT1) receptors. Perinatal lack of AT1 receptor stimulation leads to long-term renal damage that is characterized by tubulointerstitial inflammation/fibrosis, papillary atrophy and renal vascular changes. Irreversible morphologic abnormalities are associated with a pronounced disability in urine concentration. The inadvertent use of angiotensin-converting enzyme (ACE) inhibitors or AT1 receptor blockers in pregnant women causes neonatal oliguria and renal tubular dysplasia. These findings highlight the pivotal role of the RAS in human nephrogenesis. Generally, the present study attempted to construct the sequence of early morphologic-mechanistic events in the developing kidney of the rat subjected to neonatal pharmacologic blockade of the RAS, focusing on the role of the RAS in tubulogenesis. Specifically, this study: 1) determined the time course of tubular structural and inflammatory changes in the developing renal medulla; 2) identified genes involved in the RAS-mediated developmental process of the renal medulla; 3) characterized developmental defects of the thick ascending limb of Henle (TALH); and 4) characterized developmental defects of the tubules at a subcellular level. The following methods were employed in the present study: light and electron microscopy; stereological analysis; DNA microarrays, Western blotting and immunohistochemistry; flow cytometry and spectrophotometric analysis. The present study demonstrated that pharmacologic interruption of AT1 receptor signaling in the newborn rat induces irreversible medullary tubular changes, firstly, and triggers an inflammatory response, secondly. Perturbed tubulogenesis is associated with, and may partly result from, alterations in the assembly of extracellular matrix and nephrovascular development. Neonatal lack of ANG II stimulation causes phenotypic changes in the developing TALH. Developmental defects in the TALH provide an explanatory support for the reduced sodium reabsorption and disability to concentrate urine in adult rats subjected to neonatal inhibition of the RAS. Furthermore, early structural and functional changes in the mitochondria of the developing tubular cells devoid of ANG II stimulation provide the propensity for the tubular developmental defect. Altogether, this thesis presents an advanced pathogenetic insight into the RAS-mediated renal tubulogenesis in the rat

Neonatal losartan treatment suppresses renal expression of molecules involved in cell-cell and cell-matrix interactions

Lack of neonatal angiotensin II type 1 receptor (AT(1)) stimulation produces renal abnormalities characterized by papillary atrophy and impaired urinary concentrating ability, but the mechanisms involved are still unclear. DNA microarray was used to identify genes that are differentially expressed in renal medulla in response to neonatal treatment with AT(1) receptor antagonist losartan (30 mg/kg per d), which commenced within 24 h after birth. The data showed that losartan treatment for 48 h downregulated 68 genes, approximately 30% of which encode various components of cytoskeleton and cytoskeleton-associated proteins, extracellular matrix, and enzymes involved in extracellular matrix maturation or turnover. With the use of immunohistochemistry and Western immunoblot, the microarray data were confirmed and it was demonstrated that losartan suppressed renal expression of syndecan 2, alpha-smooth muscle actin, MHC class II, and leukocyte type 12-lipoxygenase by day 4. In addition, losartan inhibited medullary expression of integrin alpha6 and caused relocalization of integrins alpha6 and alpha3. Moreover, losartan inhibited cell proliferation in medullary tubules by day 9, as detected by Ki-67 immunostaining. This study provides new data supporting the contention that a lack of AT(1) receptor stimulation results in abnormal matrix assembly, disturbed cell-cell and cell-matrix interactions, and subsequent abnormal tubular maturation. Moreover, regulation of the expression of leukocyte type 12-lipoxygenase and alpha-smooth muscle actin by the renin-angiotensin system in the immature kidney adds new knowledge toward the understanding of renal vascular development