Application of Hanging Drop Technique for Kidney Tissue Culture.

BACKGROUND/AIMS: The hanging drop technique is a well-established method used in culture of animal tissues. However, this method has not been used in adult kidney tissue culture yet. This study was to explore the feasibility of using this technique for culturing adult kidney cortex to study the time course of RNA viability in the tubules and vasculature, as well as the tissue structural integrity. METHODS: In each Petri dish with the plate covered with sterile buffer, a section of mouse renal cortex was cultured within a drop of DMEM culture medium on the inner surface of the lip facing downward. The tissue were then harvested at each specific time points for Real-time PCR analysis and histological studies. RESULTS: The results showed that the mRNA level of most Na+ related transporters and cotransporters were stably maintained within 6 hours in culture, and that the mRNA level of most receptors found in the vasculature and glomeruli were stably maintained for up to 9 days in culture. Paraffin sections of the cultured renal cortex indicated that the tubules began to lose tubular integrity after 6 hours, but the glomeruli and vasculatures were still recognizable up to 9 days in culture. CONCLUSIONS: We concluded that adult kidney tissue culture by hanging drop method can be used to study gene expressions in vasculature and glomeruli.

[Investigation of renal corticomedullary differentiation with age-related change on non-contrast-enhanced MRI].

OBJECTIVE: To evaluate the relationship between renal corticomedullary differentiation, renal cortical thickness and age-related changes with non-contrast-enhanced steady-state free precession(SSFP) magnetic resonance imaging (MRI) and spatially selective inversion recovery(IR) pulse technology as well as its applied value . METHODS: A total of 76 healthy volunteers had been recruited from August 2014 to June 2015 in First Hospital of China Medical University.All volunteers were divided into three groups: 2-40 years old, 41-60 years old, 61-80 years old. All 76 volunteers underwent non-contrast-enhanced steady-state free precession(SSFP) 3.0 T MRI scan using variable inversion times (TIs)(TI=1 000, 1 100, 1 200, 1 300, 1 400, 1 500, 1 600, 1 700 ms). The renal corticomedullary differentiation was observed and the signal intensity of renal cortex and medulla were measured respectively as well in order to calculate renal corticomedullary contrast ratio. Besides, renal cortical thickness and renal size were measured. RESULTS: All 76 volunteers were successfully performed all the sequences of MRI scan, including 152 useful imaging of kidney in total. The renal corticomedullary differentiation was clearly shown in all subjects. There was negative correlation between the optimal inversion time(TI) and age(r=-0.65, P<0.01). Similarly, negative correlation was observed between renal corticomedullary contrast ratio and age(r=-0.35, P<0.01). The mean renal cortical thickness of all subjects was (5.33±0.71)mm and there were statistically significant difference among those different groups, which was negative-related with age(r=-0.79, P<0.01). There was no statistically significant difference between sexuality and renal cortical thickness.Additionally, renal cortical thickness had no statistically significant difference in both sides of kidneys. CONCLUSION: The renal corticomedullary differentiation is depicted clearly by means of non-contrast-enhanced steady-state free precession MRI with spatially selective inversion recovery pulse technology. The optimal inversion time decreases along with the increase of age. In the meanwhile, the renal cortical thickness could be measured truthfully and accurately.

[THE ROLE OF THE PI3-KINASE IN THE FAST NONGENOMIC ALDOSTERONE EFFECTS IN THE PRINCIPAL CELLS OF THE CORTICAL COLLECTING DUCT OF THE RAT KIDNEY IN THE POSTNATAL ONTOGENESIS].

The involvement of wortmannin (10 -5 M), phosphatidyl inositol 3-kinase (PI3K) blocker, in the implementation of the rapid nongenomic aldosterone (10 nM) effects on the intracellular sodium (Na i +) and the principal cell volume of cortical collecting duct (CCD) of 10-day and adult rat kidney CCD was studied. Using fluorescence microscopy with intracellular dye Na Green and Calcein we found that wortmannin weakened the effect of aldosterone on the Na i + at low sodium in the extracellular medium (14 mM NaCl), and slowed the rate of reduction of the principal cell volume in the presence of aldosterone at the hypoosmotic shock (240/140 mOsm) since 10 days of age. The findings suggest the participation of phosphatidylinositol pathway in the fast nongenomic aldosterone effects (seconds and minutes) at the early stage of postnatal ontogenesis.

Different expressions of large-conductance Ca2+-activated K+ channels in the mouse renal cortex and hippocampus during postnatal development.

Large-conductance Ca(+)-activated K(+) (BKCa) channels are widely distributed in a variety of cells and play a pivotal and specific role in many pathophysiological conditions. However, the function of BK(Ca) channels in the kidney cortex and hippocampus during the postnatal development has not received attention. In this study, to elucidate the role of BK(Ca) channels during the development, it is essential to establish the location and quantitation of expression of BK(Ca). The expressions of BK(Ca) were detected in the kidney and hippocampus on postnatal days (P) 1, 3, 5, 7, 14, 21, 28, and 49 by immunohistochemical and Western blot analysis. Our results showed that expressions of BK(Ca) channels were found in tubules and corpuscles at all time points. The expression was also observed at all developmental stages of the renal corpuscles, such as comma-shaped body, S-shaped body, renal corpuscles of stage III, and renal corpuscles of stage IV. During the development, the expression of BK(Ca) channels was decreased and the most prominent change of BK(Ca) protein level appeared between P14 and P21. In contrast, BK(Ca) channels were expressed in all regions of the hippocampus at every time point with the level increasing during the early development (P1 to P14). The findings of the present study suggest that BKCa channels play an important role during the postnatal development in both the renal cortex and hippocampus.

Age-related change in renal corticomedullary differentiation: evaluation with noncontrast-enhanced steady-state free precession (SSFP) MRI with spatially selective inversion pulse using variable inversion time.

PURPOSE: To evaluate age-related change in renal corticomedullary differentiation and renal cortical thickness by means of noncontrast-enhanced steady-state free precession (SSFP) magnetic resonance imaging (MRI) with spatially selective inversion recovery (IR) pulse. MATERIALS AND METHODS: The Institutional Review Board of our hospital approved this retrospective study and patient informed consent was waived. This study included 48 patients without renal diseases who underwent noncontrast-enhanced SSFP MRI with spatially selective IR pulse using variable inversion times (TIs) (700-1500 msec). The signal intensity of renal cortex and medulla were measured to calculate renal corticomedullary contrast ratio. Additionally, renal cortical thickness was measured. RESULTS: The renal corticomedullary junction was clearly depicted in all patients. The mean cortical thickness was 3.9 ± 0.83 mm. The mean corticomedullary contrast ratio was 4.7 ± 1.4. There was a negative correlation between optimal TI for the best visualization of renal corticomedullary differentiation and age (r = -0.378; P = 0.001). However, there was no significant correlation between renal corticomedullary contrast ratio and age (r = 0.187; P = 0.20). Similarly, no significant correlation was observed between renal cortical thickness and age (r = 0.054; P = 0.712). CONCLUSION: In the normal kidney, noncontrast-enhanced SSFP MRI with spatially selective IR pulse can be used to assess renal corticomedullary differentiation and cortical thickness without the influence of aging, although optimal TI values for the best visualization of renal corticomedullary junction were shortened with aging.

The pine-cone body: an intermediate structure between the cap mesenchyme and the renal vesicle in the developing nod mouse kidney revealed by an ultrastructural study.

Nephrogenesis is mainly characterized by the interaction of two distinct renal constituents, the ureteric bud and the metanephric mesenchyme. In this paper we describe by means of light and electron microscopic techniques the morphological events that take place during the early stages of cap mesenchymal formation. Samples of normal renal tissue were excised from newborn NOD mice and processed by standard light and electron microscopy techniques. In all samples examined we detected the presence of several cap mesenchymal aggregates in different stages of differentiation. They varied from small solid nodules with few ovoid cells to bigger pine-cone-like aggregates, characterized by a peculiar distribution and morphology of their cellular constituents. Our data highlight, for the first time, the presence of a specific cap mesenchymal structure, the pine-cone body and show, at ultrastructural level, how each cap aggregate epithelializes proceeding in stages from a condensed mesenchymal aggregate to the renal vesicle, through the intermediate "pine-cone body" stage.

The expression of EPOR in renal cortex during postnatal development.

Erythropoietin (EPO), known for its role in erythroid differentiation, has been shown to be an important growth factor for brain and heart. EPO is synthesized by fibroblast-like cells in the renal cortex. Prompted by this anatomical relationship and its significant impact on the maturation process of brain and heart, we asked whether EPO could play a role during the development of renal cortex. The relationship between the development of renal cortex and the change of EPO receptor (EPOR), through which EPO could act as a renotropic cytokine, became interesting to us. In this study, the day of birth was recorded as postnatal day 0(P0). P7, P14, P21, P28, P35, P42 and mature mice (postnatal days>56) were used as the animal model of different developmental stages. Immunohistochemistry and Western blotting were used to detect the expression of EPOR in mouse renal cortex. Results showed that expression of EPOR decreased with the development of renal cortex and became stable when kidney became mature. The expression of EPOR was detected at the renal tubule of all developmental stages and a relatively higher expression was observed at P14. However, at the renal corpuscle the expression was only observed at P7 and quickly became undetectable after that. All these suggested that a translocation of EPOR from renal corpuscle to renal tubule may take place during the developmental process of renal cortex. Also, EPO may be an essential element for the maturation of renal cortex, and the requirement for EPO was changed during postnatal development process.

Expression of TRPC6 in renal cortex and hippocampus of mouse during postnatal development.

TRPC6, a member of the TRPC family, attracts much attention from the public because of its relationship with the disease. In both the brain and kidney, TRPC6 serves a variety of functions. The aim of the present study was to observe the expression and effects of TRPC6 in renal cortex and hippocampus during early postnatal development of the mouse. In the present study, immunohistochemistry and Western blotting were used to detect the expression of TRPC6 in the mouse kidney and hippocampus of postnatal day 1, 3, 5, 7, 14, 21, 28 and 49 (P1, P3, P5, P7, P14, P21, P28 and P49). Results showed that the expression of TRPC6 was increased in the mouse hippocampus, and there was a significant increase between P7 and P14 during the postnatal development. Meanwhile, the expression of TRPC6 was also detected in glomerulus and tubules, and a decreased expression was found during postnatal maturation of mouse renal cortex. From these in vivo experiments, we concluded that the expression of TRPC6 was active in the developing mouse kidney cortex, and followed a loss of expression with the development of kidney. Meanwhile, an increased expression was found in the hippocampus with the development. Together, these data suggested that the developmental changes in TRPC6 expression might be required for proper postnatal kidney cortex development, and played a critical role in the hippocampus during development, which formed the basis for understanding the nephrogenesis and neurogenesis in mice and provided a practically useful knowledge to the clinical and related research.

Na+,K+-ATPase activity and subunit protein expression: ontogeny and effects of exogenous and endogenous steroids on the cerebral cortex and renal cortex of sheep.

We examined the effects of development, exogenous, and endogenous glucocorticoids on Na(+),K(+)-ATPase activity and subunit protein expression in ovine cerebral cortices and renal cortices. Ewes at 60%, 80%, and 90% gestation, newborns, and adults received 4 dexamethasone or placebo injections. Cerebral cortex Na(+),K(+)-ATPase activity was higher (P < .05) in placebo-treated newborns than fetuses of placebo-treated ewes and adults, α(1)-expression was higher at 90% gestation than the other ages; α(2)-expression was higher in newborns than fetuses; α(3)-expression was higher in newborns than 60% gestation; ß(1)-expression was higher in newborns than the other ages, and ß(2)-expression higher at 60% than 80% and 90% gestation, and in adults. Renal cortex Na(+),K(+)-ATPase activity was higher in placebo-treated adults and newborns than fetuses. Cerebral cortex Na(+),K(+)-ATPase activity was higher in dexamethasone- than placebo-treated adults, and α(1)-expression higher in fetuses of dexamethasone- than placebo-treated ewes at 60% and 80% gestation. Renal cortex Na(+),K(+)-ATPase activity and α(1)-expression were higher in fetuses of dexamethasone- than placebo-treated ewes at each gestational age, and ß(1)-expression was higher in fetuses of dexamethasone- than placebo-treated ewes at 90% gestation and in dexamethasone- than placebo-treated adults. Cerebral cortex Na(+),K(+)-ATPase activity, α(1)-expression, ß(1)-expression, and renal cortex α(1)-expression correlated directly with increases in fetal cortisol. In conclusion, Na(+),K(+)-ATPase activity and subunit expression exhibit specific developmental patterns in brain and kidney; exogenous glucocorticoids regulate activity and subunit expression in brain and kidney at some ages; endogenous increases in fetal cortisol regulate cerebral Na(+),K(+)-ATPase, but exogenous glucocorticoids have a greater effect on renal than cerebral Na(+),K(+)-ATPase.

A novel, low-volume method for organ culture of embryonic kidneys that allows development of cortico-medullary anatomical organization.

Here, we present a novel method for culturing kidneys in low volumes of medium that offers more organotypic development compared to conventional methods. Organ culture is a powerful technique for studying renal development. It recapitulates many aspects of early development very well, but the established techniques have some disadvantages: in particular, they require relatively large volumes (1-3 mls) of culture medium, which can make high-throughput screens expensive, they require porous (filter) substrates which are difficult to modify chemically, and the organs produced do not achieve good cortico-medullary zonation. Here, we present a technique of growing kidney rudiments in very low volumes of medium-around 85 microliters-using silicone chambers. In this system, kidneys grow directly on glass, grow larger than in conventional culture and develop a clear anatomical cortico-medullary zonation with extended loops of Henle.

Prominin-2 is a novel marker of distal tubules and collecting ducts of the human and murine kidney.

Prominin-1 (CD133) and its paralogue, prominin-2, are pentaspan membrane glycoproteins that are strongly expressed in the kidney where they have been originally cloned from. Previously, we have described the localization of prominin-1 in proximal tubules of the nephron. The spatial distribution of prominin-2, however, has not yet been documented in the kidney. We therefore examined the expression of this molecule along distinct tubular segments of the human and murine nephron using in situ hybridization and immunohistochemistry. Our findings indicated that human prominin-2 transcripts and protein were confined to distal tubules of the nephron including the thick ascending limb of Henle's loop and the distal convoluted tubule, the connecting duct and to the collecting duct system. Therein, this glycoprotein was enriched at the basolateral plasma membrane of the tubular epithelial cells with exception of the thick ascending limb where it was also found in the apical domain. This is in contrast with the exclusive apical localization of prominin-1 in epithelial cells of proximal nephron tubules. The distribution of murine prominin-2 transcripts was reminiscent of its human orthologue. In addition, a marked enrichment in the epithelium covering the papilla and in the urothelium of the renal pelvis was noted in mice. Finally, our biochemical analysis revealed that prominin-2 was released into the clinically healthy human urine as a constituent of small membrane vesicles. Collectively our data show the distribution and subcellular localization of prominin-2 within the kidney in situ and its release into the urine. Urinary detection of this protein might offer novel diagnostic approaches for studying renal diseases affecting distal segments of the nephron.

Effect of retinoic acid on renal development in newborn mice treated with an angiogenesis inhibitor.

BACKGROUND: A mouse model of impaired renal development was developed and the effect of retinoic acid (RA) was investigated in this animal model. METHODS: An angiogenesis inhibitor (SU1498) was injected s.c. into day 3 C57BL/6 newborn mice to create a model of arrested renal development. RA (2 mg/kg) was injected i.p. for 10 days. Morphometry and immunohistochemistry were done. RESULTS: Mice injected with SU1498 demonstrated deranged renal development in tubular structure and glomerular tuft area. Cortical thickness and area of glomerular tuft were significantly decreased after vascular endothelial growth factor (VEGF) inhibitor, and were significantly restored by RA. The length of capillary loops/glomerulus, the number of podocytes/glomerulus, and density of peritubular capillaries on CD31 immunostaining were significantly decreased by VEGF blocking and recovered by RA. CONCLUSIONS: VEGF plays a major role in renal development, and RA reverses the inhibited development caused by an angiogenesis inhibitor.

The long-term label retaining population of the renal papilla arises through divergent regional growth of the kidney.

Long-term pulse chase experiments previously identified a sizable population of BrdU-retaining cells within the renal papilla. The origin of these cells has been unclear, and in this work we test the hypothesis that they become quiescent early during the course of kidney development and organ growth. Indeed, we find that BrdU-retaining cells of the papilla can be labeled only by pulsing with BrdU from embryonic (E) day 11.25 to postnatal (P) day 7, the approximate period of kidney development in the mouse. BrdU signal in the cortex and outer medulla is rapidly diluted by cellular proliferation during embryonic development and juvenile growth, whereas cells within the papilla differentiate and exit the cell cycle during organogenesis. Indeed, by E17.5, little or no active proliferation can be seen in the distal papilla, indicating maturation of this structure in a distal-to-proximal manner during organogenesis. We conclude that BrdU-retaining cells of the papilla represent a population of cells that quiesce during embryonic development and localize within a region of the kidney that matures early. We therefore propose that selective papillary retention of BrdU arises through a combination of regionalized slowing of, and exit from, the cell cycle within the papilla during the period of ongoing kidney development, and extensive proliferative growth of the juvenile kidney resulting in dilution of BrdU below the detection level in extra-papillary regions.

Glomerular eNOS gene expression during postnatal maturation and AT1 receptor inhibition.

Glomerular maturation increases from immature superficial to advanced juxtamedullary nephrons, while nephrogenesis continues postnatally in porcine kidneys. Endothelial NOS, eNOS, shows significant postnatal renal developmental regulation, perhaps mediated by Angiotensin II (AII). The objective was to compare eNOS mRNA gene expression between superficial and juxtamedullary glomeruli obtained from piglets and adult pigs utilizing laser capture microdissection during basal conditions and, to determine the role of the AII AT1 receptor, AT1, after chronic AT1 inhibition (AT1X) with candesartan. Superficial glomerular eNOS expression was lowest in newborns (NB) and at 7 days, and was highest in 14, 21 day old piglets and adults. Juxtamedullary glomerular eNOS, while similar in NB, 14, 21 day and adult, dipped to the lowest level at 7 days. Juxtamedullary glomerular eNOS expression in the NB was 7 fold greater than in superficial glomeruli. AT1X did not change eNOS expression in adult glomeruli. AT1X significantly reduced NB eNOS expression in both superficial, 90+/-10%, and juxtamedullary glomeruli, 89+/-5% respectively. In conclusion, eNOS gene expression demonstrates significant differences between NB superficial and juxtamedullary glomeruli, significant postnatal developmental regulation of both glomerular locations, and this expression may be mediated in the NB by AII via the AT1 receptor.

Sex-differential expression of ornithine aminotransferase in the mouse kidney.

The mouse kidney expresses the gene of ornithine aminotransferase (Oat). Previous works suggest that Oat is differentially expressed in female and male mouse kidney (Alonso E, Rubio V. Biochem J 259: 131-138, 1989; Levillain O, Diaz JJ, Blanchard O, Dechaud H. Endocrinology 146: 950-959, 2005; Manteuffel-Cymborowska M, Chmurzynska W, Peska M, Grzelakowska-Sztabert B. Int J Biochem Cell Biol 27: 287-295, 1995; Natesan S, Reddy SR. Comp Biochem Physiol B Biochem Mol Biol 130: 585-595, 2001; Yu H, Yoo PK, Aguirre CC, Tsoa RW, Kern RM, Grody WW, Cederbaum SD, Iyer RK. J Histochem Cytochem 51: 1151-1160, 2003). This study was designed to provide a detailed description of the sexual dimorphism of Oat expression in the mouse kidney and to test the influence of sex hormones on its regulation. Experiments were performed on male and female Swiss OF1 mice during their postnatal development, at adulthood, and in orchidectomized and ovariectomized mice. Kidneys, dissected renal zones, and mitochondria were used to analyze OAT mRNA and protein levels and measure OAT activity. The results revealed that before puberty, Oat expression was similar between female and male kidneys whereas from puberty until adulthood Oat expression increased in the female kidney, becoming approximately 2.5-fold higher than in the male kidney. This sex-differential expression of Oat was associated with a sex-specific distribution of Oat along the corticopapillary axis and within the nephron. OAT was three- to fourfold more expressed in the female than the male cortex. In males, Oat was highly expressed in the medulla, mainly in the thick ascending limbs. Renal Oat distribution in orchidectomized mice resembled that in the females. Ovariectomy did not influence Oat expression. Sex differences are explained by the physiological increase in plasma testosterone in males. Expression of medium-chain acyl-CoA synthetase protein confirmed this finding. We report sexual dimorphism of Oat expression in the mouse kidney and show that Oat is naturally downregulated in the presence of testosterone.

Protein kinase B, P34cdc2 kinase, and p21 ras GTP-binding in kidneys of aging rats.

Renal nephropathy present in male Wistar rats more than 13 months of age was reported as an indication that the rats were in renal failure. In this study, the renal tissue damage at 14 months of age in male Munich Wistar rats was similar to that reported for Wistar rats, indicating that Munich Wistar rats could be another model for study of kidney function in the aging rat. The usual renal response to injury involves increased cell division and/or reparative processes that involve tyrosine kinase activity (TyrK) and/or guanosine triphosphate-binding (G) protein signal trans-duction pathways. This study reveals the presence of renal tissue damage coinciding with significantly reduced activity of Ras, Akt, and p34cdc2 kinase, the signaling proteins that regulate cell division and/or growth, in renal cortical tissues of aging rats compared to young rats (P < 0.005, P < 0.005, and P< 0.001, respectively). These results suggest that proteins involved in signal transduction pathways associated with cell replication are downregulated in the aging kidney cortex at a time when renal cellular damage is also present.

Morphometric index of the developing murine kidney.

Mammalian kidney morphogenesis begins when the ureteric bud (UB) induces surrounding metanephric mesenchyme to differentiate into nephrons, the functional units of the mature organ. Although several genes required for this process have been identified, the mechanisms that control final nephron number and the localization of distinct tubular segments to cortical and medullary zones of the kidney remain poorly understood. This finding is due, in part, to the lack of quantitative studies describing the acquisition of mature renal structure. We have analyzed the following parameters of the developing murine kidney throughout embryogenesis: nephron and UB tip number, distance between UB branch points and total kidney, and cortical and medullary volume. Results of this morphometric analysis reveal previously unrecognized changes in the pattern of UB growth and rate of nephrogenesis. In addition, this morphometric index provides a much-needed reference for accurately describing renal patterning defects exhibited by genetically altered mice.

Rat renal cortical OAT1 and OAT3 exhibit gender differences determined by both androgen stimulation and estrogen inhibition.

In rats, the secretion of p-aminohippurate (PAH) by the kidney is higher in males (M) than in females (F). The role of the major renal PAH transporters, OAT1 and OAT3, in the generation of these gender differences, as well as the responsible hormones and mechanisms, has not been clarified. Here we used various immunocytochemical methods to study effects of gender, gonadectomy, and treatment with sex hormones on localization and abundance of OAT1 and OAT3 along the rat nephron. Both transporters were localized to the basolateral membrane: OAT1 was strong in proximal tubule S2 and weak in the S3 segments, whereas OAT3 was stained in proximal tubule S1 and S2 segments, thick ascending limb, distal tubule, and in principal cells along the collecting duct. Gender differences in the expression of both transporters in adult rats (M > F) were observed only in the cortical tubules. OAT1 in the cortex was strongly reduced by castration in adult M, whereas the treatment of castrated M with testosterone, estradiol, or progesterone resulted in its complete restitution, further depression, or partial restitution, respectively. In adult F, ovariectomy weakly increased, whereas estradiol treatment of ovariectomized F strongly decreased, the expression of OAT1. The expression of OAT3 in the M and F cortex largely followed a similar pattern, except that ovariectomy and progesterone treatment showed no effect, whereas in other tissue zones gender differences were not observed. In prepubertal rats, the expression of OAT1 and OAT3 in the kidney cortex was low and showed no gender differences. Our data indicate that gender differences in the rat renal cortical OAT1 and OAT3 (M > F) appear after puberty and are determined by both a stimulatory effect of androgens (and progesterone in the case of OAT1) and an inhibitory effect of estrogens.

Low endogenous glucocorticoid allows induction of kidney cortical cyclooxygenase-2 during postnatal rat development.

In postnatal weeks 2-4, cyclooxygenase-2 (COX-2) is induced in the rat kidney cortex where it is critically involved in final stages of kidney development. We examined whether changes in circulating gluco- or mineralocorticosteroids or in their renal receptors regulate postnatal COX-2 induction. Plasma corticosterone concentration peaked at birth, decreased to low levels at days 3-13, and increased to adult levels from day 22. Aldosterone peaked at birth and then stabilized at adult levels. Gluco- and mineralocorticoid receptor (GR and MR) mRNAs were expressed stably in kidney before, during, and after COX-2 induction. 11 beta-hydroxysteroid dehydrogenase 2 was induced shortly after birth and was widely distributed in the whole collecting duct system in the suckling period and then returned to an adult pattern. Supplementation with corticosterone (20 mg.kg-1.day-1) or GR-specific dexamethasone (1 mg.kg-1.day-1) during low endogenous corticosterone suppressed renal COX-2 mRNA and protein and led to a restricted distribution of COX-2 immunolabeling. The ability of glucocorticoids to affect COX-2 was reflected in colocalization of GR-alpha and COX-2 immunoreactivity and mRNAs in thick ascending limb of Henle's loop. The MR antagonist potassium canrenoate (20 mg.kg-1.day-1) enhanced COX-2 expression from days 5 to 10, but low MR-specific concentrations of DOCA (1 mg.kg-1.day-1) had no effect on COX-2. Renomedullary interstitial cells expressed GR-alpha and COX-2. Dexamethasone suppressed COX-2 in these cells. Thus low plasma concentrations of corticosterone allowed for cortical and medullary COX-2 induction during postnatal kidney development. Increased circulating glucocorticoid in the postnatal period may damage late renal development through inhibition of COX-2.

Cell proliferation and morphometric changes in the rat kidney during postnatal development.

We have investigated the temporal maturation of the rat kidney during the postnatal developmental period. As a result, we observed the following: an active process of cortical cell proliferation and differentiation occurs as late as day 20. The medulla is the most immature zone at birth and displays the greatest morphological changes during this period. At birth, no distinction exists between inner and outer medulla, and the outer and inner strip of the outer medulla can be distinguished as late as day 30. Remodeling of the ECM surrounding collecting ducts occurs in the medulla twice, stopping at day 11 and it occurs in the papilla three times, stopping at day 20. The increase of kidney size is temporally different for each kidney zone. The cortex and the papilla acquire the morphological appearance of the adult kidney before the medulla does. Consequently, the medulla remains at the highest degree of immaturation among the kidney zones for a relatively long postnatal period.