Medullary Thickness Research Articles

Longitudinal assessment of mouse renal injury using high-resolution anatomic and magnetization transfer MR imaging

The purpose of this study is to evaluate the utility of high-resolution non-invasive endogenous high-field MRI methods for the longitudinal structural and quantitative assessments of mouse kidney disease using the model of unilateral ureter obstruction (UUO). T1-weighted, T2-weighted and magnetization transfer (MT) imaging protocols were optimized to improve the regional contrast in mouse kidney. Conventional T1 and T2 weighted images were collected in UUO mice on day 0 (~3h), day 1, day 3 and day 6 after injury, on a 7T small animal MRI system. Cortical and medullary thickness, corticomedullary contrast and Magnetization Transfer Ratio (MTR) were assessed longitudinally. Masson trichrome staining was used to histologically assess changes in tissue microstructure. Over the course of UUO progression there were significant (p<0.05) changes in thickness of cortex and outer medulla, and regional changes in T2 signal intensity and MTR values. Histological changes included tubular cell death, tubular dilation, urine retention, and interstitial fibrosis, assessed by histology. The MRI measures of renal cortical and medullary atrophy, cortical–medullary differentiation and MTR changes provide an endogenous, non-invasive and quantitative evaluation of renal morphology and tissue composition during UUO progression.

Gastrointestinal and Dental Morphology of Herbivorous Mammals: Where does the Laotian Rock Rat Fit?

We studied dental complexity in Laoncistes aenigmomus to place this unique rodent species into a comparative context. The complexity of cheek teeth of Laoncistes are within the range of that for omnivorous mammals feeding predominantly on plants or that for herbivorous mammals. In a comparative sample of predominantly herbivorous hystricomorph rodents, only the degu (Octodon degus) and the chinchilla (Chinchilla chinchilla) have less complex cheek teeth than Laonastes. We also used ethanol fixed stomachs and a silicone cast of stomach of five Laonastes to study its macroscopic and microscopic gut anatomy. The stomach of Laonastes has four elongated chambers that are partially sacculated. The stomach of Laonastes differs microscopically from the typical rodent stomach: most of the epithelium is glandular, and non-glandular stratified squamous epithelium can be found only in the sulcus that is microscopically homogenous. Microscopic screenings showed that the digesta was similar in all stomach compartments. The mean renal medullary thickness (RMT) in this species is low indicating that its ability to concentrate electrolytes in the urine is low. We discuss the dentition and the stomach morphology of Laonastes in relation to observations on its natural diet.

Fetal kidneys: additional sonographic criteria of normal development

The aim of this study was to establish objective criteria for the evaluation of cortical echogenicity (CE), cortical thickness (CT), and medullary thickness (MT), as well as the corticomedullary ratio (CMR), throughout gestation. In this prospective single-center study, CE, MT, CT, and CMR were evaluated in a group of singleton pregnancies examined by ultrasound during the second and third trimesters. The CE evolved from a hyperechoic pattern compared with the liver or spleen during early second trimester to a hypoechogenic pattern in the third trimester, with no fetus displaying cortical hyperechogenicity after 32 weeks. CT increased from 1.8 to 2.5 mm (p < 0.05) from 21 to 25 to 34 to 37 weeks; MT from 2.7 to 5.1 mm (p < 0.0001), and the CMR decreased from 0.7 to 0.5 (p < 0.001). The CE, CT, and MT evolve with gestation. Cortical hyperechogenicity compared with the liver or spleen after 32 weeks or a CMR above 0.7 in the third trimester should raise the suspicion of a fetal nephropathy.

Ultrasonographic Features of the Chinchilla (Chinchilla lanigera) Kidney

Nine healthy chinchillas (Chinchilla lanigera) were used to characterize the ultrasonographic size and anatomical structure of the kidneys. Sonographic evaluations were performed with the aid of a 12-MHz linear probe. Kidney measurements included total width and length, total organ area, cortex and medullary thickness, and width and length of the renal pelvis. Based on the results of this study, normal chinchilla kidneys are located retroperitoneally, with the right kidney in a more cranial location than the left. Statistical analysis showed that measurements were similar between contralateral kidneys and between sexes. Chinchilla kidneys have a single papilla and a wider renal pelvis compared with the renal pelvis of dogs and cats. Moreover, chinchilla kidneys have a longer medullary area. The data herein may aid diagnosis of renal disease in chinchillas, avoiding misinterpretations of ultrasonic findings involving the kidneys of this species.

Renal dimensions at ultrasonography in healthy Ragdoll cats with normal kidney morphology: correlation with age, gender and bodyweight.

Fifty-six healthy Ragdoll cats underwent an ultrasonographical examination of the urinary tract to evaluate if gender, age, bodyweight and presence of a medullary rim sign had a significant influence on renal length and corticomedullary ratio (CM). Individual variation percentage was much more pronounced for renal length in comparison with CM ratio. Mean renal length measured 3.83 ± 0.45 cm (range 2.98-5.09 cm), mean cortical thickness 0.73 ± 0.15 cm (range 0.36-1.18 cm), mean medullary thickness 0.87 ± 0.19 cm (range 0.46-1.39 cm) and mean CM ratio 0.88 ± 0.29 (range 0.29-1.78). Renal length showed a significant positive correlation with bodyweight (P <0.0001), age (P = 0.0073) and male gender (P <0.0001). Therefore, these parameters have to be kept in mind when evaluating renal length on ultrasound. The CM ratio was solely influenced by the presence of a medullary rim sign (P <0.0001). Further research, however, is needed to investigate the usefulness of the CM ratio for the detection of kidney disease by ultrasonography.

PHYSIOLOGICAL DIVERSITY WITHIN AND AMONG WOOD MICE (APODEMUS) SPECIES IN ISRAEL

ABSTRACT Diversity of thermoregulatory variables and relative medullary thickness (RMT) of the kidney were compared among three Apodemus species in Israel, as well as between two populations of A. mystacinus from two different habitats. Significant differences in thermoregulatory abilities were found between the two populations of A. mystacinus, from Mount Carmel and Mount Hermon, as well as among A. mystancinus, A. hermonensis, and A. flavicollis. The highest RMT, 7.40 ± 0.26, was found in A. flavicollis, supporting the idea that this species is excluded by A. mystacinus, (RMT = 6.09 ± 0.41) into relatively more xeric habitats.

Correlation of Inflammation with Adrenocortical Atrophy in Canine Adrenalitis

Hypoadrenocorticism or Addison's disease (AD) is a functional disorder in which insufficient mineralocorticoid and glucocorticoid hormones are produced by the adrenal cortex. Human AD is usually attributed to lymphoplasmacytic adrenalitis with autoimmune destruction of the adrenal cortex. Lymphoplasmacytic adrenalitis is also reported in some descriptions of canine AD; however, the histological aspects of adrenalitis or adrenocortical atrophy have not been well characterized because microscopical examination is not required for diagnosis of AD. In this study, sections of adrenal glands from 33 dogs with adrenalitis were compared with those of 37 dogs without adrenal lesions. The affected dogs were classified clinically as having AD (n = 3), being suspected of having AD (n = 17), not having AD (n = 11) or were unclassified (n = 2). The adrenal inflammation was lymphoplasmacytic in 17 dogs, lymphocytic in four, lymphohistiocytic in one, granulomatous in three and neutrophilic in eight cases. Adrenal glands from control dogs lacked leucocyte infiltration and had a cortical to medullary area ratio of 1.1-7.2. All three dogs with AD, 8/17 dogs with suspected AD and 1/11 dogs without AD had a cortical to medullary area ratio <1.1. Because the area ratio was correlated (r = 0.94) with a linear cortical to medullary thickness ratio, a thickness ratio <1.1 could also indicate severe adrenocortical atrophy. Severe adrenocortical atrophy was associated typically with lymphoplasmacytic infiltration and nearly complete loss of cortical cells; however, the zona glomerulosa was partially spared in three dogs with lymphoplasmacytic adrenalitis and severe cortical atrophy. In contrast, non-lymphoid inflammation was generally part of systemic disease, multifocal and was unaccompanied by severe adrenocortical atrophy.

Effects of Uninephrectomy on Morphological and Histological Measurements of the Remnant Kidney in a Goat (Capra hircus) Model

The objective of this study was to investigate the effects of uninephrectomy (UNX) on compensatory morphological and histological measurements of the remnant kidney in adult female Nubian goats. Animals were either subjected to surgical extirpation of the left kidney or sham operation was performed. The kidneys were weighed and their size was measured, and the morphological and histological measurements were performed. The weight and volume of the remnant right kidney were significantly increased in the UNX compared to sham-operated animals. After three weeks, the volume increased by 83.16 % compared with the volume of the control (sham-operated). After three months of the operation, the volume of UNX increased by 56.45% compared with the volume of the kidney of the control. The relative medullary thickness (RMT) of contralateral kidney increased by 21.88% compared with the value of the kidneys of the control. The diameter of glomerulus increased by 18.19%, proximal tubule 68.56% and the distal tubule by 46.28%, but Bowman space increased by 31.66%. The study indicates that the goat model can be adopted to investigate the effects of nephrectomy.

Comparison of renal ultrasonographic measurements between healthy cats of three cat breeds: Ragdoll, British Shorthair and Sphynx.

Healthy cats of three cat breeds -- Sphynx (n = 11), British Shorthair (n = 15) and Ragdoll (n = 15) -- were included in this study. All cats underwent an ultrasonographic examination to assess renal length, cortical thickness, medullary thickness and corticomedullary ratio. Of all ultrasonographic measurements, renal length showed the highest variation. For all ultrasonographic dimensions, individual and kidney side (left vs right) variation were much more pronounced than interbreed variation. Sphynx cats tended to have larger kidneys (4.09 ± 0.33 cm) than British Shorthair (3.77 ± 0.43 cm) and Ragdoll cats (3.87 ± 0.41 cm). British Shorthair cats, however, tended to have a thinner cortex (0.67 ± 0.13 cm) and medulla (0.76 ± 0.18 cm) than Sphynx (0.76 ± 0.14 cm and 0.90 ± 0.25 cm, respectively) and Ragdoll cats (0.75 ± 0.13 cm and 0.91 ± 0.22 cm, respectively). However, statistical tests did not reveal significant differences between these cat breeds. The corticomedullary ratio was similar for the three cat breeds (Sphynx: 0.93 ± 0.43; British Shorthair: 0.91 ± 0.26; Ragdoll: 0.88 ± 0.31). The left kidney (3.83 ± 0.42 cm) was significantly smaller than the right kidney (3.99 ± 0.40 cm) and showed a thicker medulla (left: 0.93 ± 0.21 cm, right: 0.79 ± 0.22 cm), and thus a lower corticomedullary ratio (left: 0.80 ± 0.23, right: 1.01 ± 0.32). For the cortical thickness, no significant difference was observed between the left (0.71 ± 0.14 cm) and right kidney (0.74 ± 0.14 cm).

Cortical bone and ridge thickness of hyperdivergent and hypodivergent adults

The purpose of this study was to assess differences in dentoalvolar cortical bone thickness between hyperdivergent and hypodivergent young adults. Pretreatment cone-beam computed tomography images of 57 patients, including 30 hypodivergent subjects (22 women, 8 men) and 27 hyperdivergent subjects (20 women, 7 men), were analyzed. The data were imported into imaging software (version 10.5; Dolphin Imaging Systems, Chatsworth, Calif); standardized orientations were used to measure buccal and lingual cortical bone thicknesses at 16 interradicular sites of the maxilla and the mandible. Total alveolar ridge thickness and medullary space thickness were measured at the same sites. T tests showed significant (P<0.05) group differences, with hypodivergent subjects having significantly thicker buccal cortices. The lingual cortex of the maxilla was also significantly thicker in the hypodivergent than in the hyperdivergent subjects. Alveolar ridge thickness was significantly greater at all sites of the hypodivergent mandible and at the anterior 2 sites of the hypodivergent maxilla. Medullary thickness was significantly greater only in the hypodivergent mandibles between the first molars and the second premolars, and between the first and second premolars. Buccal cortical bone was significantly thicker than lingual cortical bone in the mandible; lingual bone was significantly thicker in the maxilla. Cortical bone tends to be thicker in hypodivergent than in hyperdivergent subjects. This explains the concomitant differences in alveolar ridge thickness. Medullary space thickness is largely unaffected by facial divergence.

Synergic Effects of Levamlodipine and Bisoprolol on Blood Pressure Reduction and Organ Protection in Spontaneously Hypertensive Rats

Stroke is a major cause of disability and death worldwide. Hypertension is one of the most important risk factors for stroke. The objective of this work was to study the synergic effects of levamlodipine and bisoprolol on blood pressure reduction and organ protection in spontaneously hypertensive rats (SHR). Blood pressure was continuously monitored in conscious SHR. For acute study, a single dose of drugs was administrated via an intragastric catheter. For chronic study (4 months), drugs were delivered via rat chow. A single dose of levamlodipine (from 1 mg/kg), bisoprolol (from 0.125 mg/kg), and their combinations significantly decreased blood pressure. The levamlodipine-induced tachycardia and the bisoprolol-induced bradycardia were temporized by the combination of these two drugs. Upon chronic treatment, this combination also decreased blood pressure variability and reduced organ damage. Levamlodipine and bisoprolol produce synergic effects on blood pressure reduction and organ protection in SHR.

Update in pediatric renal sonography: focus on hyperechoic kidneys

For years, US has been the primary modality for monitoring growth and development of the kidneys before and after birth. Good knowledge of the normal imaging appearances of the kidney is mandatory in order to diagnose renal disease. One of the main objectives of sonography is to detect and evaluate congenital uropathies. The definition of urinary tract dilatation is standardized, and the role of US is essential and clearly defined for this diagnosis. Still, we need long-term follow-up in order to correlate the degree of dilatation and renal function. More recently, thanks to highdefinition transducers, more attention has been given to characterization of nephropathies through more careful analysis of the renal cortex and medulla. Cortico-medullary differentiation (CMD; determined by the different tissue characteristics of the cortex and medulla) is a well-established characteristic of renal sonography in neonates and young children. The CMD can be visualized already around 18–20 weeks’ gestation. In the fetus, the thickness of both cortex and medulla increases progressively throughout pregnancy; yet medullary thickness increases more rapidly than cortical thickness, and therefore the cortico-medullary ratio decreases (from 0.5 around 20 weeks’ to 0.4 around 32 weeks’ gestation). Notably, the overall echogenicity of the fetal renal parenchyma decreases with time. It is hyperechoic relative to the liver or spleen during the second trimester and becomes relatively isoor hypo-echoic after 32 weeks’ gestation. Based on these normal references, it is possible to diagnose various nephropathies prenatally (polycystic kidney diseases, nephrotic syndrome, renal vein thrombosis, etc). After birth, there is a massive fluid overload in the kidneys, and this renders the renal parenchyma relatively hyperechoic. This feature is more marked in prematures, but can be observed in term neonates. As mentioned above, CMD is always visualized. The cortico-medullary ratio should be around 0.38. An abnormal ratio can be observed in various conditions. For instance, in smallfor-dates newborns it is decreased to 0.30, whereas in diseases such as congenital nephrotic syndrome, the pyramids will appear small and irregular and the CMD will be difficult to assess. The sonographic pattern of the CMD has become an essential feature for analysis. The CMD can be increased, absent or reversed, and each pattern will suggest a list of differential diagnoses. Reversed CMD (with hyperechoic medulla) or areas of increased echogenicity in the kidney is referred to as “nephrocalcinosis”, and has been the focus of much research. Medullary nephrocalcinosis is the commonest form; it has been linked to hypercalciuria and metabolic diseases. For some, genetic studies are mandatory in order to distinguish between the diagnostic possibilities. Hyperoxaluria type I, proximal tubular acidosis and Dent syndrome are among other diseases that can be diagnosed by the sonographic patterns. Cortical nephrocalcinosis is less frequent. Distinctive patterns of localized or diffuse areas of calcification may Disclaimer Dr. Fred Avni has no financial interests, investigational or off-label uses to disclose.

Cortical Thickness of the Second Metatarsal After Correction of Hallux Valgus

Hallux valgus is a functional deformity of the first ray. When incorrectly aligned, the first ray is less effective as a support structure, and the stresses then theoretically transfer to the second metatarsal which could lead to increased cortical density. The aim of this study was to evaluate if surgical correction of hallux valgus lead to changes in the cortical density of the second metatarsal. This was a retrospective study involving 13 patients who had surgery for isolated hallux valgus. The average postoperative followup was 16 (range, 11 to 24) months. We analyzed pre- and postoperative radiographs of the feet. We assessed the variations in the medial and lateral cortical thickness, the medullary thickness and the shaft thickness (ST) of the second and fourth metatarsals. A significant reduction of the medial cortical bone thickness of the second metatarsal (MT2) (p < 0.001) and a significant medullary increase of MT2 (p < 0.001) were observed postoperatively. However, no significant difference in the lateral cortical thickness or shaft thickness of the metatarsal was found. A significant reduction of the MCT/ST ratio (p < 0.001) was also observed. Regarding the fourth metatarsal, which was used as a control, no significant change was observed. The isolated cortical variations of the second metatarsal suggests that isolated hallux valgus correction led to a redistribution of the stresses on to the first ray.

Correlation between prenatal urinary matrix metalloproteinase activity and the degree of kidney damage in a large animal model of congenital obstructive uropathy

Background/Purpose We aimed to determine whether the profile of matrix metalloproteinase (MMP) activity in fetal urine correlates with the degree of kidney damage in the setting of congenital obstructive uropathy. Methods Fetal lambs underwent either a sham operation or creation of a complete urinary tract obstruction. Necropsies were performed before term, when urinary MMP profiling was performed by zymography; and kidney damage was assessed histologically by multiple semiquantitative analyses and histomorphometric measurements. Results There was a significant correlation between inner medullary thickness and MMP-9 ( P = .005) and 63-kd MMP-2 ( P = .019) activities. In like manner, the only MMPs associated with kidney fibrosis were MMP-9 and 63-kd MMP-2. Matrix metalloproteinase–9 activity was a highly significant independent predictor of the total combined kidney fibrosis score ( P < .001) as well as of higher fibrosis grades in each of 6 kidney areas analyzed (all with P < .01). The activity of 63-kd MMP-2 correlated significantly with higher fibrosis in select areas. Conclusions In a fetal ovine model, urinary MMP activity correlates with the degree of kidney damage. The presence of MMP-9 (in particular) and that of 63-kd MMP-2 are independent predictors of severity. Prenatal urinary MMP profiling may enhance patient stratification and counseling in the setting of congenital obstructive uropathy.

Variation in urine concentrating ability and water balance of the Black-tailed Tree Rat Thallomys nigricauda, along an aridity gradient

Mechanisms behind variation in physiological traits may assist in explaining how certain traits have evolved. The ability of mammals to concentrate urine has been seen as an adaptation to xeric environments. Urine osmolality and relative medullary thickness (RMT) are two indices which indicate urine concentrating powers. In addition, mammals living in xeric regions have lower water turnover rates (WTR) than their mesic counterparts. The RMT, urine concentrating ability (UCA) and WTR of the Black-tailed Tree Rat, Thallomys nigricauda, were investigated at three study sites along an aridity gradient. We investigated the extent to which these traits are influenced by evolutionary adaptation and/or phenotypic flexibility. There was no significant difference in RMT between sites and no difference in osmolalities when site and season were taken into account. In addition, there was no significant effect of site and season on WTR. This suggests that these traits might have a genetic basis, and reflect an evolutionary adaptation. Lack of differences in the renal traits in T. nigricauda across their range may be interpreted as lack of phenotypic flexibility. However, as a consequence of the degree of individual variation in the parameters measured there appears to be phenotypic flexibility with individuals responding to their specific conditions. This has positive implications for the survival of the species in the light of climate change.

Localization of aquaporin-2, renal morphology and urine composition in the bottlenose dolphin and the Baird’s beaked whale

This study examined the distribution pattern of aquaporin-2 (AQP2), relative medullary thickness (RMT) and urine properties in the bottlenose dolphin Tursiops truncatus and Baird's beaked whale Berardius bairdii. Immunohistochemical studies revealed that AQP2 was localized in the collecting tubules/ducts of both species' renicules, as in terrestrial mammals. The collecting ducts with AQP2 were thinner and arranged more densely in the dolphin than in the whale. RMT values in the renicule were moderate in both species, but were significantly higher in the dolphin (6.0 +/- 0.9) than the whale (4.9 +/- 0.7). Urine of the bottlenose dolphin is comparatively concentrated (osmolality: 1715.7 +/- 279.4 mOsm kg(-1), Na(+): 490.1 +/- 87.9 mmol l(-1), Cl(-): 402.7 +/- 79.6 mmol l(-1), K(+): 80.7 +/- 25.8 mmol l(-1), urea nitrogen: 703.5 +/- 253.9 mmol l(-1)), while urine of the dead Baird's beaked whale is less concentrated (osmolality: 837.5 +/- 293.8 mOsm kg(-1), Na(+): 192.9 +/- 81.5 mmol l(-1), Cl(-): 159.9 +/- 71.4 mmol l(-1), K(+): 44.3 +/- 29.5 mmol l(-1), urea nitrogen: 270.7 +/- 120.3 mmol l(-1)). These data suggest it is possible that the differences in these renal morphological features may be related in some way to the difference in urine composition between the species, although further studies are necessary.

Relationships between renal morphology and diet in 26 species of new world bats (suborder microchiroptera)

The renal morphology of 24 species of mormoopid and phyllostomid bats feeding on six different diets was examined to test evolutionary changes in several structural traits presumably led by dietary shifts from ancestral insectivorous diets. The kidneys of a fish-eating vespertilionid and an insect-eating emballonurid were also examined but not included in the phylogenetic comparison. The length, width, and breadth of the kidneys were used to calculate relative medullary thickness (RMT). Tissues were processed for stereological analysis, and the volumes of the kidney, nephron components, and vasculature were determined. RMT did not correlate with body mass in either animal-eating or plant-eating phyllostomid and mormoopid bats. The shift from insectivory to frugivory and nectarivory was accompanied by a reduction in RMT, a reduction in the percent of renal medulla, and an increase in the percent of renal cortex. No changes in these traits were observed in bats that shifted to carnivorous, omnivorous or sanguinivorous habits. No changes were observed in renal vasculature, in the percentage of cortical and medullary nephron components or of capillaries surrounding the nephrons in any feeding group. Vespertilionid and emballonurid species had similar values in all traits examined as compared to insectivorous phyllostomids and mormoopids. Our data suggest that diet does not influence a single area of the nephron, but rather the entire nephron such that the relative amounts of renal cortex and medulla are affected.

Diet salinity and vasopressin as reproduction modulators in the desert-dwelling golden spiny mouse ( Acomys russatus)

The time for reproduction in mammals largely depends on the availability of water and food in their habitat. Therefore, in regions where rains are limited to definite seasons of the year, mammals presumably will restrict their breeding correspondingly. But while mammals living in predictable ecosystems would benefit by timing their season to an ultimate predictable cue, such as photoperiod, in unpredictable ecosystems (e.g., deserts) they will need to use a more proximate signal. We suggest a mechanism by which water shortage (low water content in plants) could act as a proximate cue for ending the reproductive season. The golden spiny mouse ( Acomys russatus), a diurnal rodent living in extreme deserts, may face an increased dietary salt content as the summer progresses and the vegetation becomes dry. Under laboratory conditions, increased diet salinity lead to reproductive hiatus in females, notable in imperforated vagina, and a significant decrease in the ovaries, uteri, and body masses. In females treated with vasopressin (VP), a hormone expressed during water stress, the uteri and body masses have decreased significantly, and the ovaries exhibited an increased number of atretic follicles. VP has also led to a significant decrease in relative medullary thickness (RMT) of the kidney. It is thus suggested that VP could act as a modulator linking the reproductive system with water economy in desert rodents, possibly through its act on the energetic pathways.

Renal Structural Adaptations among Three Species of Peccary

Several morphological characteristics of the kidney were studied to determine the degree of interspecific and intraspecific adaptation that might occur within 3 species of peccary from arid, semi-arid, and moist habitats.Paired kidney samples were collected from collared (Tayassu tajacu), Chacoan (Catagonus wagneri), and white-lipped (T. pecari) peccaries from habitats varying in water availability. Two indexes for renal concentrating ability, the relative medullary thickness and relative medullary area, exhibited higher values for animals from arid and semi-arid habitats than for those from moist habitats. Relative kidney mass also was higher for collared peccaries from dry environments. It was concluded that renal structures are flexible in response to environment variation, and the differences observed were related to the adaptability of renal concentrating structures.

Inter- and intraspecific variation in the use of marine food resources by three Cinclodes (Furnariidae, Aves) species: carbon isotopes and osmoregulatory physiology

The avian genus Cinclodes (Furnariidae) includes species that inhabit both inland and marine shores. We compared the carbon isotopic composition and osmoregulatory capacities of field caught individuals of three Cinclodes species in Chile. Cinclodes nigrofumosus is a resident of coastal shores, whereas C. oustaleti and C. patagonicus inhabit both coastal and inland environments. The tissues of C. nigrofumosus exhibited distinctively marine delta(13)C values, whereas those of C. oustaleti and C. patagonicus were intermediate between marine and terrestrial values. The differences in carbon isotopic composition among these three species were paralleled by differences in osmoregulatory characteristics. The species that carbon isotopes revealed to be strictly marine, C. nigrofumosus, had relatively larger kidneys with a higher fraction of total renal tissue occupied by medullary cones than its congeners C. oustaleti and C. patagonicus. Cinclodes nigrofumosus individuals also produced more concentrated urine. In addition to interspecific differences in osmoregulation, we found intraspecific differences. Cinclodes nigrofumosus collected at an arid site with limited or no available fresh water exhibited larger kidneys and higher relative medullary thickness than individuals collected at a mesic site. Cinclodes nigrofumosus, like all passerines, lacks functional salt glands. This species appears to be unique among passerines in its ability to live in extreme arid coastal environments and to cope with a marine diet that imposes high osmotic loads.