Stereological assessment of normal Persian squirrels (<Emphasis Type="Italic">Sciurus anomalus</Emphasis>) kidney

The functions of the mammalian kidney are closely related to its structure. This suggests that renal function can be completely characterized by accurate knowledge of its quantitative morphological features. The aim of this study was to investigate the histomorphometric features of the kidney using design-based and unbiased stereological methods in the Persian squirrel (Sciurus anomalus), which is the only representative of the Sciuridae family in the Middle East. The left kidneys of five animals were examined. Total volume of the kidney, cortex, and medulla were determined to be 960.75 ± 87.4, 754.31 ± 77.09 and 206.1 ± 16.89 mm³, respectively. The glomerular number was 32844.03 ± 1069.19, and the total glomerular volume was estimated to be 36.7 ± 1.45 mm³. The volume and length of the proximal convoluted tubule were estimated at 585.67 ± 60.7 mm³ and 328.8 ± 14.8 m, respectively, with both values being greater than those reported in the rat kidney. The volume and length of the distal convoluted tubule were calculated at 122.34 ± 7.38 mm³ and 234.4 ± 17.45 m, respectively, which are also greater than those reported in the rat kidney. Despite the comparable body weight, the total number and mean individual volume of glomeruli in the Persian squirrel kidney were greater than those in the rat kidney. Overall, the stereological variables of the kidneys elucidated in this study are exclusive to the Persian squirrel. Our findings, together with future renal physiological data, will contribute to a better understanding of the renal structure–function relationship in the Persian squirrel.     

Morphology of the kidney of the platypus (Ornithorhynchus anatinus: Monotremata)

The platypus kidney shows morphological similarities to those of other mammals. Macroscopically, the cortex is easily distinguishable from the fairly wide medulla. Within the medulla, no clear border is observed between the inner and outer zones. Light and transmission electron microscopically, the glomeruli show quite similar architecture to those of other mammals; however, the glomerular lobulation is very clear. The glomerular tufts are rather simple, but capillary lumen varies widely in size, which is one of the unique features of the platypus kidney. The urinary tubule is generally similar to that of human and other mammals in shape and segmentation; however, the staining specificities of histochemical reactions and the shape of epithelial cells of the Henle's loop differ from those ofother mammals. The most conspicuous features are: 1) although no protein casts are found in the tubular lumina, epithelial cells of the proximal convoluted tubule (PCT) have numerous electron-dense vesicles as in human nephrotic kidneys; and 2) the platypus Henle's loop consists of the thick epithelial cells similar to the mammalian type nephron of birds. As compared to those of other mammals such as humans and rats, our observations suggest that the platypus kidney is less developed, in terms of evolution.© Willey-Liss, Inc.     

PTH sensitive adenyl cyclase activity in different segments of the rabbit nephron

Summary PTH sensitive adenylate cyclase activity was measured in 9 different segments of the nephron, isolated by microdissection from collagenase-treated rabbit kidney slices.The enzyme of the following segments was stimulated by PTH, 1 U/ml: PCT. (proximal convoluted tubule); PR (pars recta); CAL (cortical portion of the thick ascending limb); DCT (distal convoluted tubule); BCT (first, branched portion of the collecting tubule); the segments which did not respond to PTH were: TDL (thin descending limb); MAL (medullary portion of the thick ascending limb); CCT (cortical portion of the collecting tubule distally adjacent to BCT); MCT (collecting tubule from the outer medulla).PTH sensitive adenylate cyclase per mm tubule in PR was half that measured in PCT.Half maximal stimulation corresponded to 50–100 mU/ml PTH (1–2×10^–8M) in both PCT and PR, and to about 350 mU/ml in CAL. PTH (1 U/ml) stimulation factors ranged from 5 to 60 depending on the structures.It is concluded that in addition to PCT and PR, CAL and BCT might be target structures involved in the physiological actions of PTH on the kidney.This work was supported by a grant from the C.N.R.S. to the LRA n^o 219.     

Insulin receptors along the rat nephron: [125I] Insulin binding in microdissected glomeruli and tubules

Binding of [¹²⁵I] Tyr A¹⁴ human insulin ([¹²⁵I] insulin) was measured at 4°C in glomeruli and pieces of tubule microdissected from collagenase-treated rat kidneys. For glomeruli and all segments tested, total and non specific binding increased linearly with glomeruli number or tubular length. When determined with 4.0 nM labelled hormone, the distribution of specific binding sites (expressed as 10^–18 mol [¹²⁵I] insulin bound per glomerulus or mm tubule length) was as follows: glomerulus, 2.5±0.3; proximal convoluted tubule (PCT), 12.6±0.6; pars recta (PR), 4.0±2.3; thin descending limb (TDL), 0.6±0.2; thin ascending limb (TAL), 0.6±0.2; medullary thick ascending limb (MAL), 0.8±0.1; cortical ascending limb (CAL), 2.1±0.1; distal convoluted tubule (DCT), 5.6±1.1; cortical collecting tubule (CCT), 3.2±0.3 and outer medullary collecting tubule (MCT), 2.3±0.1. Specific [¹²⁵I] insulin binding to glomeruli and tubule segments was time- and dose-dependent, saturable, reversible after elimination of free labelled ligand, and inhibited by unlabelled human insulin. When analysed in Scatchard and Hill coordinates, the binding data revealed a negative cooperation in the interaction processes between [¹²⁵I] insulin and glomerular and tubular binding sites, with apparent dissociation constants and Hill coefficients of the following values: glomerulus, 0.6 nM and 0.60; PCT, 10.0 nM and 0.55; MAL, 4.3 nM and 0.80; CAL, 2.0 nM and 0.74; CCT, 7.6 nM and 0.80 and MCT, 1.0 nM and 0.57 respectively. The stereospecificity of nephron binding sites was assessed in competitive experiments showing that unlabelled bovine and procine insulins were as efficient as human insulin for displacing [¹²⁵I] insulin, whereas A and B chains of insulin and unrelated peptide hormones were almost inactive. These results indicate that the detected [¹²⁵I] insulin binding sites may correspond to physiological insulin receptors.Abbreviations used [¹²⁵I] Insulin [¹²⁵I] Tyr A¹⁴ human insulin - PCT proximal convoluted tubule - PR pars recta - TDL thin descending limb - TAL thin ascending limb - MAL medullary thick ascending limb - CAL cortical ascending limb - DCT distal convoluted tubule - CCT cortical collecting tubule - MCT outer medullary collecting tubule     

Localization of tubular uptake segment of filtered Cystatin C and Aprotinin in the rat kidney

Aim: The renal tubular uptake of ¹²⁵I‐Aprotinin (*Ap) is on average located more superficially than its filtration site, causing transfer of some of *Ap filtered in deep to more superficial cortical zones. ¹²⁵I‐Cystatin C (*Cy) showed less uptake in deep cortical zones than Ap, suggesting a longer and/or a more superficial tubular uptake site. To test that hypothesis and to quantify the outward transfer of the filtered polypeptides, we estimated the tubular uptake pattern of the tracers in perfusion fixed rat kidneys after intravenous injection of *Cy and *Ap. Methods: Autoradiographs were made from 10 μm thick slices of Microfil nephron casts from outer (OC), middle (MC) and inner (IC) cortical zones to quantify cortical border‐crossing *Ap transfer. Single nephron glomerular filtration rate (snGFR) was estimated as the zonal uptake of *Ap corrected for *Ap transfer, divided by its time‐integrated plasma concentration and the zonal number of glomeruli. Results: *Ap and *Cy uptake fell exponentially along the proximal convoluted tubule (PCT), indicating an uptake proportional to luminal concentration. Uptake in IC exceededx that in MC and OC nephrons. The per cent PCT length with *Cy uptake (67.2 ± 1.6) exceeded that of *Ap (54.6 ± 1.8). The zonal border‐crossing PCT length (29–34% of total PCT) from deep to more superficial cortical zones transferred 4–6% more *Cy than *Ap. Conclusion: Greater tubular uptake length of *Cy than of *Ap causes more cortical border‐crossing of *Cy. The zonal snGFR estimated from Aprotinin uptake corrected for border‐crossing agreed well with that obtained with the Hanssen ferrocyanide technique.     

Acute kidney injury in human leptospirosis: an immunohistochemical study with pathophysiological correlation

Tubulointerstitial nephritis is a common clinicopathological finding in leptospirosis. Clinically, nonoliguric acute kidney injury (AKI), hypokalemia, sodium, and magnesium wasting frequently occur in leptospirosis. The exact mechanisms of renal involvement remain largely unclear. Immunohistochemistry to detect expression of the endogenous sodium/hydrogen exchanger isoform 3 (NHE 3), aquaporin 1 and 2, α-Na⁺K⁺ATPase, and sodium–potassium–chloride cotransporter in its NKCC2 isoform was performed on kidneys removed during autopsy of human leptospirosis cases and kidneys removed during autopsy of human non-leptospirosis cases with and without evidence of acute tubular necrosis (ATN). A decrease in NHE 3, aquaporin 1, and α-Na⁺K⁺ATPase expression occurred in proximal convoluted tubule cells. Expression of aquaporin 1 was preserved along the descending thin limb of the loop of Henle in the outer medulla. α-Na⁺K⁺ATpase expression was essentially preserved in the distal tubules, i.e., the thick ascending limb of the loop of Henle, macula densa, and distal convoluted tubule. Aquaporin 2 expression in the collecting tubules was enhanced compared to those of non-leptospirotic kidneys. NKCC2 cotransport isoform was expressed in the thick ascending limb of the loop of Henle and was essentially preserved in leptospirotic kidneys. Primary injury of the proximal convoluted tubules is regarded as the hallmark of the kidney in leptospirosis. Sodium and water transport are particularly affected with increased distal potassium excretion, hypokalemia, and polyuria. Enhanced expression of aquaporin 2 in medullary collecting tubules is probably an attempt to retain water during the nonoliguric phase of renal failure.     

Distribution of glomerular density in different cortical zones of the human kidney

Our studies have demonstrated that a low glomerular density in renal biopsies is a plausible predictor of a worse renal outcome in patients with primary glomerular diseases. However, there remains a concern regarding the diversity that may exist in the distribution of glomerular density within the same kidney. This study therefore aimed to determine the differences in the glomerular density between anatomically different cortical zones of the human kidney. A total of 89 autopsy kidneys were analyzed to accurately measure the glomerular density in different parts of the renal cortex. As a whole, compared to the glomerular density in the superficial cortex (3.0 ± 0.7/mm²), the average glomerular density in the juxtamedullary cortex (2.2 ± 0.6/mm²) was approximately two‐thirds. The glomerular density showed maximal 3.5‐fold variations between individuals and was inversely correlated with the mean glomerular volume in both cortical areas. A low glomerular density of the superficial cortex was predominantly associated with the increase of global glomerulosclerosis. On the other hand, a low glomerular density of the juxtamedullary cortex was predominantly associated with an increase in the kidney weight. Thus, there are significant zonal differences in the distribution of the glomerular density in human kidneys independent of the potential variations observed between individuals.     

小鼠肾远曲小管三维可视化研究

目的 肾远曲小管（DCT）是肾单位最后一段小管,其与相邻小管的分界及走行的毗邻关系是理解肾形态发生中集合管与肾单位连接方式,以及该段小管参与水盐代谢调节机制的重要结构基础。本实验在肾组织连续切片基础上,采用微细结构三维可视化技术,建立小鼠肾远曲小管的空间走行。 方法 C57/BL/6 J小鼠灌流固定后取肾,垂直于肾长轴切取组织块,树脂812包埋,从肾被膜到肾外髓外带获得2.5 μm厚连续切片720张,获取数字化显微镜图像并通过计算机程序进行配准,追踪来自3只小鼠共90个肾单位远曲小管,观察其空间走行并测量其长度。 结果 肾远曲小管起始于远端小管致密斑后40～180 μm处,上皮由矮柱状或立方陡然变为高柱状,细胞核靠近腔面,走行在皮质迷路其自身的肾小球周围,区域相对独立,末端向被膜方向逐渐移行为连接小管;此处上皮再次变矮,细胞核排列不局限在近腔面。浅层皮质肾单位的远曲小管在回旋返折最高处接触肾被膜1次。远曲小管长度为500～900 μm。 结论 远曲小管较短且盘曲走行,较少与其他小管交错,所以区域较小而独立,可能有助于该节段的吸收功能受激素的精准调节。     

Glucagon receptors along the nephron: [125I]glucagon binding in rat tubules

Binding of [¹²⁵I]glucagon was measured in microdissected pieces of tubules from the rat nephron. Specific glucagon binding sites were found only in nephron segments containing a glucagon-sensititive adenylate cyclase activity. At 7.5 nM labelled hormone, higher levels of specific binding (16–27×10^–18 mol mm^–1) were found in the thick ascending limb of the Henle's loop and in the distal convoluted tubule and lower binding levels (2–5×10^–18 mol mm^–) in the collecting tubule whereas specific binding could not be detected in the proximal tubule and in the thin segments of the Henle's loop. In the medullary thick ascending limb, Scatchard analysis of specific [¹²⁵I]glucagon binding indicated an apparent equilibrium dissociation constant of 2.4 nM. The stereospecificity of binding sites in medullary thick ascending limbs and medullary collecting tubules, was assessed by competition experiments using unlabelled glucagon, enteroglucagon and unrelated hormones (vasopressin, calcitonin, parathyroid hormone and insulin); in both segments, glucagon was more active than enteroglucagon in displacing labelled glucagon from its tubular binding sites, whereas all other hormones tested were inactive. These results indicate that tubule binding sites might be the physiological receptors for glucagon involved in adenylate cyclase activation.Abbreviations PCT proximal convoluted tubule - TDL thin descending limb - TAL thin ascending limb - MAL medullary thick ascending limb - CAL cortical ascending limb - DCT distal convoluted tubule - CCT cortical collecting tubule - MCT medullary collecting tubule     

The role of the convoluted segment of the proximal tubule in the disposal of 131I-insulin in the rat kidney

It is generally accepted that in the kidney insulin is metabolized in the proximal tubule, but whether in the convoluted segment, the straight segment, or both has not been established. By means of autoradiography counting of radioactivity, and interrupted flow techniques, the following observations have been made. ¹³¹I-labelled porcine insulin is metabolized exclusively in the convoluted segment of the proximal tubule. Although the glomerular filtrate is the major source of insulin supply to the renal epithelia, the peritubular capillary plexuses provide as much as 30% or more of the total insulin delivered to the renal epithelia. The epithelium of the convoluted segment is capable of sequestering ¹³¹I-insulin from the peritubular capillary plexuses, a phenomenon which has not been established previously.     

Anatomical and functional heterogeneity of nephrons in the rabbit: Microdissection studies and SNGFR measurements

Summary The single nephron glomerular filtration rate (SNGFR) was determined in superficial (S) and juxtamedullary (JM) nephrons of 10 anesthetized rabbits by the¹⁴C ferrocyanide infusion technique. The length of the proximal tubules and the volume of the glomeruli were also determined for the same nephrons. SNGFR was higher in JM than in S: 28.6±3.4 versus 22.6±3.0 nl/min,P<0.001. In JM nephrons, glomeruli were larger than in S: 1.3±0.1 versus 0.9±0.1 nl,P<0.001, whereas there was no difference between proximal tubule length in either category (S, 8.7±0.3 and JM, 8.9±0.5 mm). In 6 out of 8 animals, SNGFR was significantly correlated to glomerular volume. Lack of correlation was observed between SNGFR and length of proximal tubule in all animals but one. These results show that the rabbit, as well as small rodents and the dog, has a higher SNGFR in juxtamedullary than superficial glomeruli. Although this functional difference is not related to the length of the proximal tubule in each individual animal, the ratio between the mean SNGFR value and the mean length of the proximal tubule in superficial rabbit nephrons is similar to the ratio found in other species.     

High‐resolution diffusion tensor imaging of the human kidneys using a free‐breathing,multi‐slice,targeted field of view approach

Fractional anisotropy (FA) obtained by diffusion tensor imaging (DTI) can be used to image the kidneys without any contrast media. FA of the medulla has been shown to correlate with kidney function. It is expected that higher spatial resolution would improve the depiction of small structures within the kidney. However, the achievement of high spatial resolution in renal DTI remains challenging as a result of respiratory motion and susceptibility to diffusion imaging artefacts. In this study, a targeted field of view (TFOV) method was used to obtain high‐resolution FA maps and colour‐coded diffusion tensor orientations, together with measures of the medullary and cortical FA, in 12 healthy subjects. Subjects were scanned with two implementations (dual and single kidney) of a TFOV DTI method. DTI scans were performed during free breathing with a navigator‐triggered sequence. Results showed high consistency in the greyscale FA, colour‐coded FA and diffusion tensors across subjects and between dual‐ and single‐kidney scans, which have in‐plane voxel sizes of 2 × 2 mm² and 1.2 × 1.2 mm², respectively. The ability to acquire multiple contiguous slices allowed the medulla and cortical FA to be quantified over the entire kidney volume. The mean medulla and cortical FA values were 0.38 ± 0.017 and 0.21 ± 0.019, respectively, for the dual‐kidney scan, and 0.35 ± 0.032 and 0.20 ± 0.014, respectively, for the single‐kidney scan. The mean FA between the medulla and cortex was significantly different (p < 0.001) for both dual‐ and single‐kidney implementations. High‐spatial‐resolution DTI shows promise for improving the characterization and non‐invasive assessment of kidney function. © 2014 The Authors. NMR in Biomedicine published by John Wiley & Sons, Ltd.     

Acute renal denervation causes time-dependent resetting of the tubuloglomerular feedback mechanism

Renal effects of acute renal denervation (DNX) were studied in anaesthetized rats. In a first series, whole kidney clearance measurements were made 120 and 240 min after unilateral DNX. At 240 min, urine production was 3.59±0.87 μL min^-1 in control kidneys and 7.74±1.97 μL min^-1 in denervated kidneys. The corresponding values for sodium excretion were 0.56±0.17 and 1.41±0.34 μmol min^-1, potassium excretion 0.48±0.08 and 0.97±0.37 μmol min^-1 and glomerular filtration rate (GFR) 0.83±0.08 and 1.05±0.16 mL min^-1, respectively. In a second series, tubuloglomerular feedback (TGF) characteristics were determined with the stop-flow pressure (P_sf) technique. With increasing time, the sensitivity of the TGF mechanism diminished in denervated rats, as indicated by an increased turning point (TP). TP was significantly increased 2 h after DNX from 19.1±1.13 in control to 25.9±1.10 nL min^-1. TP was further increased 4 h after DNX to 37.3±3.12 nL min^-1. However, the maximal TGF response to increased flow in the late proximal tubule was not altered. But, P_st was significantly higher in DNX rats than in the controls (47.4±1.01 vs. 43.0±1.53 mmHg) in spite of a lower blood pressure (107±2.9 vs. 119±2.2 mmHg). We conclude that intact renal nerves are essential for the setting of the TGF sensitivity and hence the regulation of GFR     

硒酸锌金属自显影技术检测游离锌离子在小鼠肾脏的分布

目的研究游离锌离子在小鼠肾脏的定位分布。方法应用硒酸锌金属自显影技术(ZnSeAMG)检测小鼠肾脏内的游离锌离子分布。结果游离锌离子在肾脏内分布广泛,皮质中有大量AMG反应阳性颗粒,髓质中的AMG阳性颗粒较少。其中,近曲小管、远曲小管、近直小管和远直小管上皮细胞近腔侧均分布有大量的棕黑色AMG阳性颗粒,肾小体、细段和集合管上皮细胞中AMG阳性颗粒较少。结论小鼠肾脏内含有丰富的游离锌离子,锌离子可能参与肾脏的功能。     

脑死亡供体肾脏病理改变及移植应用标准评判的探讨

目的探讨脑死亡供体肾脏病理改变及对临床使用的指导意义。方法对13例脑死亡供体26个肾脏进行了穿刺活检,做HE染色、网状纤维染色及PAS染色。结果发现大多数患者均有不同程度的近曲小管坏死,而远曲小管、肾小球、基底膜多无改变。选择肾近曲小管上皮细胞坏死〈50%、肾小球无明显改变、肌酐〈250μmol/L、年龄〈55岁的供体26个肾脏施行了移植,均取得成功。结论脑死亡供体肾脏根据穿刺病理活检改变并结合临床表现可以作为临床移植的评判依据。     

Sites of thyroid hormone action on Na−K-ATPase along the rabbit nephron

Although Ismail-Beigi and Edelman demonstrated in 1971 that thyroid hormones control the activity of Na–K-ATPase in the mammalian kidney, the actual site of this regulation inside the organ was not located. We therefore decided to study the relationship between thyroid hormones and Na–K-ATPase activity in individual nephron segments obtained by microdissection of collagenase-treated rabbit kidneys. For this purpose, the changes in the activity and number of catalytic sites of Na–K-ATPase in response to thyroidectomy or triiodothyronine administration were examined. Eight to 12 days after thyroidectomy, Na–K-ATPase activity had dropped by 40 to 80% in the convoluted and straight portions of the proximal tubules, and in the cortical and outer medullary collecting tubules, but not in the thick ascending limbs of Henle's loops or distal convoluted tubules. The apparent number of catalytic sites for Na–K-ATPase, as measured by specific binding of³H-ouabain, decreased in parallel with Na–K-ATPase activity, and therefore this enzyme's specific activity was not altered. Fourty eight hours after injection of thyroidectomized animals with a single dose of either 100 or 500 g/kg triiodothyronine, Na–K-ATPase activity in target segments was restored to the level measured in control animals. These effects of thyroid hormone were specific for Na–K-ATPase, since the activity of adenylate cyclase, another marker of the basolateral membrane, was not altered by thyroidectomy. The results obtained indicate that triiodothyronine controls Na–K-ATPase activity in specific nephron segments, by altering the number of this enzyme's catalytic sites.Abbreviations PCT proximal convoluted tubule - PR pars recta - MAL medullary thick ascending limb of Henle's loop - CAL cortical thick ascending limb - DCT_b initial bright portion of the distal convoluted tubule - DCT_g granular portion of the distal convoluted tubule - CCT cortical collecting tubule - MCT outer medullary collecting tubule - TX thyroidectomized - T₃ triiodothyronine - AVP arginine vasopressin - PTH parathyroid hormone - ISO isoproterenol     

Atrial natriuretic peptide receptors along the rat and rabbit nephrons: [125I] α-rat atrial natriuretic peptide binding in microdissected glomeruli and tubules

Binding of [¹²⁵I] -rat atrial natriuretic peptide ([¹²⁵I] -RANP) was measured in glomeruli and pieces of tubule microdissected from rat and rabbit nephrons. High densities of specific ANP binding sites were found only in the glomeruli (10–30×10^–18 mol·glom^–1), whereas no specific binding could be detected in the proximal tubule, the thin segments of the Henle's loop, the thick ascending limb, the distal tubule and the cortical and outer medullary collecting tubules. Rising the temperature from 4° C to 35° C resulted in biphasic kinetics of binding, suggesting a temperature-dependent inactivation of labelled hormone by glomeruli. At 4° C, specific binding of [¹²⁵I] -RANP was time and dose-dependent and Scatchard analysis of data indicated an apparent equilibrium dissociation constant of 0.63 nM. Competition experiments revealed the following sequence of stereospecificity for binding to rat glomeruli: RANP 3–28>[¹²⁵I] -RANP=[¹²⁵I] -HANP=-RANP=atriopeptin III > atriopeptin II, whereas binding was unaffected by pharmacological doses of unrelated peptide hormones, prostaglandins, adrenergic agonists, dopamine, histamine and carbamylcholine. The results indicate that glomerular binding sites might be the physiological ANP receptors.Abbreviations ANP atria natriuretic peptide - 0RANP alpha rat atrial natriuretic peptide - PCT proximal convoluted tubule - PR pars recta - TDL thin descending limb - TAL thin ascending limb - MAL medullary thick ascending limb - CAL dortical thick ascending limb - DCT distal convoluted tubule - DCTb distal convoluted tubule bright - DCTg distal convoluted tubule granular - CCT conrtical collecting tubule - MCT outer medullary collecting tubule     

Type A and B monoamine oxidase activities in the human and rat kidney

The present work has examined the distribution of the two isoforms of monoamine oxidase (MAO), type MAO-A and MAO-B, in the cortex and medulla of the human and rat kidney. Homogenates of renal cortex and renal medulla were prepared in 67 mmoles 1^-1phosphate buffer (pH = 7.2) and MAO activity was determined with [³H]5-hydroxytryptamine ([³H]5HT) and [¹⁴C]β-phenylethylamine ([¹⁴C]β-PEA) as preferential substrates of type A and type B MAO, respectively. K_m and V_max values for the two substrates were also calculated. Both MAO-A and MAO-B are present in the cortex and the medulla of the human and rat kidneys. In the human kidney, MAO-A activity was found to be similar in the cortex (V_max= 142.70±45.05 nmoles mg^-1protein h^-1) and medulla (V_max= 133.91±35.51 nmoles mg^-1protein h^-1); MAO-B activity was found to be higher in the cortex (V_max= 166.19±19.75 nmoles mg¹protein h^-1) than in the medulla (V_max= 92.91±13.22 nmoles mg^-1protein h^-1). In the rat kidney, MAO-A was also found to be similar in the cortex (V_max= 62.35±1.74 nmoles mg^-1protein h^-1) and the medulla (V_max= 59.42±0.97 nmoles mg^-1protein h^-1) and higher than the activity of MAO-B in the two renal areas (cortex, V_max= 31.06±1.09 nmoles mg^-1protein h^-1; medulla, V_max= 14.93±0.97 nmoles mg^-1protein h^-1). No statistically significant differences were found between the K_m values towards [³H]5HT and [¹⁴C]β-PEA in the cortex and the medulla of the human and rat kidneys. The results show that in both renal areas, activity of the enzyme is higher in the human kidney than in the rat kidney. Furthermore, in the human kidney, in contrast with the rat kidney, MAO-B activity closely follows MAO-A activity.     

Adenylate cyclase activity along the rabbit nephron as measured in single isolated segments

Summary A method is described, which allows adenylate cyclase activity measurement in single pieces of various nephron segments. Tubular samples of 0.5 to 2 mm length were isolated by microdissection from collagenase treated slices of rabbit kidney. A photograph of each piece was taken in order to measure its length. After a permeabilisation treatment involving preincubation in a hypoosmotic medium and a freezing step, each sample was incubated for 30 min at 30°C in a medium containing high specific [-³²P]-ATP 3·10^–4 M, final volume 2.5 l.The [³²P]-cAMP formed was separated from the other labelled nucleotides by filtering the incubate on a dry aluminium oxide microcolumn;³H cAMP was added as a tracer for measuring cAMP recovery. The sensitivity of the method was found to be a few fentomoles (10^–15 M) cAMP. cAMP generation increased linearly as a function of the incubation time up to more than 30 min, and as a function of the length of the segment used.Control and fluoride (5 mM) stimulated adenylate cyclase activities were measured in the following segments of the nephron: early proximal convoluted tubule (PCT), pars recta of the proximal tubule (PR), thin descending limb of the loop (TDL), cortical portion of the thick ascending limb (CAL), distal convoluted tubule (DCT), first branched portion of the collecting tubule (BCT), further cortical (CCT) and medullary (MCT) portions of the collecting tubule.Mean control adenylate cyclase activity varied from 7 (PR) to 75 (BCT) fmoles/mm/30 min. Fluoride addition resulted in a 10 (BCT) to 50 (PR) fold increase in enzyme activity.Series of replicates gave a scatter equal to ±20% (S.D. as a per cent of the mean).The method described appears to be suitable to determine which nephron segments contain hormone-dependent adenylate cyclase.This work was supported by a grant from the C.N.R.S. to the L.R.A. 219.     

Immunohistochemical localization of osteoblast activating peptide in the mouse kidney

Osteoblast activating peptide (OBAP) is a newly discovered peptide detected in the rat stomach, which has a major role in osteogenesis. Recently, we revealed its localization in the parietal cells of the rat stomach. There have been no data regarding OBAP expression in the kidney, despite its role in calcium reabsorption in renal tubules. The current study aimed to inspect the expression of OBAP in the kidney of twelve 10-week-old male C3H/HeNJc1 mice using immunohistochemistry, and immunoelectron microscopic localization. The immunohistochemical investigation revealed an OBAP positive reaction mainly in the medulla, which was stronger than the cortex of the kidney and was concentrated in the distal convoluted tubules (DCT), connecting tubules (CT), and the thick limbs of the loop of Henle (HL). Moreover, we clarified that the OBAP was co-distributed with ghrelin and calbindin (markers of the DCT). Interestingly, immunoelectron microscopy demonstrated that OBAP was concentrated in the mitochondrial inner membrane of the DCT and CT. Based on these results, it was concluded that the mitochondria of the DCT, CT, and HL of the mice kidney generate OBAP. Furthermore, our results suggest that OBAP might have a role in the regulation of calcium reabsorption by the renal tubule; however, further investigations are required to clarify this potential role.