Development of urine concentrating ability in pouch young of a marsupial,the tammar wallaby (Macropus eugenii)

Summary During the first 28–30 weeks after birth, pouch young of the tammar wallaby (Macropus eugenii) normally produce urine less than 500 mOsm/kg and elevate their urine concentration by less than 20% when dehydrated by about 10% of body weight. The adult tammar, in contrast, can produce urine in excess of 3,000 mOsm/kg. The aim of this study was to determine when the various processes involved in urine concentration become mature in the tammar.Vasopressin was detectable in the pituitary of week-old tammars and pituitary vasopressin content decreased significantly after dehydration. Plasma vasopressin did not vary with age and dehydration was associated with an increase in plasma vasopressin levels. By 15 weeks of age at least, tammar kidney slices were able to bind vasopressin as indicated by a rise in tissue cAMP level following hormone treatment.The sodium and urea content of the renal medulla increased with age and significant gradients of these solutes were established by 25 weeks of age. Pouch young older than 25 weeks showed increased medullary sodium and urea levels following dehydration.The inability of pouch young less than 20 weeks of age to produce a highly concentrated urine does not result from any inadequacy in perception of osmotic stimuli or release of vasopressin by the pituitary or of binding of hormone by the kidney. Rather, it appears to be largely attributable to an insufficient medullary hypertonicity, particularly with respect to urea, which is consequent upon structural immaturity of the loop of Henle.Abbreviations cAMP cyclic AMP adenosine 3,5-monophosphate - AVP arginine vasopressin - LVP lysine vasopressin     

Fast and Accurate Registration of the Proximal Femurs in Bilateral Hip Joint Images by Using the Random Sub-Sample Points

Background and ObjectiveAs is known, point clouds representing the objects are frequently used in object registration. Although the objects can be registered by using all the points in the corresponding point clouds of the objects, the registration process can also be achieved with a smaller number of the landmark points selected from the entire point clouds of the objects. This paper introduces a research study focusing on the fast and accurate rigid registration of the bilateral proximal femurs in bilateral hip joint images by using the random sub-sample points. For this purpose, Random Point Sub-sampling (RPS) was analyzed and the reduced point sets were used for an accurate registration of the bilateral proximal femurs in coronal hip joint magnetic resonance imaging (MRI) slices.MethodsIn registration, bilateral proximal femurs in MRI slices were registered rigidly by performing a process consisting of three main phases named as MR image preprocessing, proximal femur registration over the random sub-sample points and MR image postprocessing. In the stage of the MR image preprocessing, segmentation maps of the bilateral proximal femurs are obtained as region of interest (RoI) images from the entire MRI slices and then, the edge maps of the segmented proximal femurs are extracted. In the registration phase, the edge maps describing the proximal femur surfaces are represented as point clouds initially. Thereafter, the RPS is performed on the proximal femur point clouds and the number of points representing the proximal femurs is reduced at different ratios. For the registration of the point clouds, the Iterative Closest Point (ICP) algorithm is performed on the reduced sets of points. Finally, the registration procedures are completed by performing MR image postprocessing on the registered proximal femur images.ResultsIn performance evaluation tests performed on healthy and pathological proximal femurs in 13 bilateral coronal hip joint MRI slices of 13 Legg-Calve-Perthes disease (LCPD) patients, bilateral proximal femurs were successfully registered with very small error rates by using the reduced set of points obtained via the RPS and promising results were achieved. The minimum error rate was observed at RPS rate of 30% as the value of 0.41 (±0.31)% on all over the bilateral proximal femurs evaluated. When the range of RPS rate of 20-30% is considered as the reference, the elapsed time in registration can be reduced by almost 30-40% compared to the case where all the proximal femur points were included in registration. Additionally, it was observed that the RPS rate should be selected as at least 25% to achieve a successful registration with an error rate below 1%.ConclusionIt was concluded from the observed results that a more successful and faster registration can be accomplished by selecting fewer points randomly from the point sets of proximal femurs instead of using all the points describing the proximal femurs. Not only an accurate registration with low error rates was performed, but also a faster registration process was performed by means of the limited number of points that are sub-sampled randomly from the whole point sets.     

DNA synthesis during larval development and compensatory growth in the mesonephros of Xenopus laevis.

Autoradiography following tritiated thymidine administration to Xenopus laevis tadpoles of stages 45–48 of larval development has revealed that, as the cells of the mesonephric kidney differentiate during organogenesis, there is a marked decrease in the percentage of cells synthesizing DNA (from 100% at stage 45 to less than 9% at stage 48). In the adult this figure is of the order of 0.1%. This reduced DNA synthetic activity was found to take place in the cells of both the proximal and distal tubules of the nephrons. Special mucous cells which serve as markers of distal tubules were not observed to synthesize DNA after the onset of their differentiation at stage 48 of larval development.Through the partial extirpation of tissue in one kidney of adult Xenopus laevis males, DNA synthesis was reactivated in differentiated cells. The increased DNA synthetic activity following partial unilateral nephrectomy was found to be maximal after 6 days of recovery when 19% of cells synthesize DNA. This increased DNA synthetic activity was found to occur only in the cells of the distal tubules, both mucous and nonmucous cells, while the cells of the proximal tubules did not respond to this reactivation.The apparent inability of proximal tubule cells to synthesize DNA following partial unilateral nephrectomy is discussed.     

The atrial natriuretic peptide (ANP) system in the pronephros and mesonephros of Bufo bufo larvae

In this study on the excretory apparatus of the Bufo bufo larvae, the ultrastructural features and the atrial natriuretic peptide (ANP)-system were examined using cytochemical and immunocytochemical methods. The early embryonic kidney, the pronephros, is replaced by a later stage, the mesonephros. The pronephros degenerates at the time of metamorphosis and the mesonephros becomes the functional kidney in the adult. Both these organs are targets for ANP, demonstrated by the presence of the specific receptors, indirectly highlighted by the cytochemical localization of the guanylate cyclase in the presence of exogenous atrial natriuretic peptide. This study concluded that the mesonephros produces ANP and thus clusters of cells containing ANP-like granules, positive to the anti-α ANP immunolocalization, were present along the mesonephric proximal tubule. The atrial natriuretic peptide system carries out an important osmoregulatory role in the excretory apparatus.     

Roles of sodium and potassium ions on p-aminohippurate transport in rabbit kidney slices.

This investigation was principally undertaken to test the ionic gradient hypothesis as applied to active p-aminohippurate uptake in the rabbit kidney cortical slice preparation. Efflux of p-aminohippurate from the slice was shown to be independent of external Na+ concentration. Transferring slices from a low sodium preincubation to a high sodium incubation medium containing p-aminohippurate increased intracellular concentrations of both Na+ and K+, and p-aminohippurate accumulation occurred. Transferring slices from a low sodium preincubation to a high sodium incubation medium containing ouabain and p-aminohippurate resulted in a net increase in intracellular Na+ concentration but no p-aminohippurate accumulation occurred. Different combinations of preincubation and incubation media gave a high to low array of intracellular Na+ concentrations and these directly reflected their respective p-aminohippurate uptake. These results suggest that the Na+ gradient hypothesis does not adequately explain the transport of organic acids in rabbit kidney. These results also suggest that Na+ possibly has an intracellular role through its stimulation of (Na+ + K+)-ATPase channeled to energizing the p-aminohippurate accumulative mechanism.     

The effects of different concentrations of glycerol and dimethylsulfoxide on the metabolic activities of kidney slices

Kidney slices either were exposed to the cryoprotectants for 1 hr at room temperature and subsequently washed and incubated in fresh KR buffer containing only the radioactive metabolic tracers, or were immediately incubated for 2 hr at 37 °C in KR buffer containing the cryoprotectant and the tracers. Exposure to glycerol by incubation of kidney slices in Krebs-Ringer bicarbonate buffer containing varying concentrations of glycerol from 0 to 70% ($\text{v}\text{v}$) resulted in a pronounced inhibitory effect on the protein synthesizing activity, while thymidine incorporation into DNA and the α-aminoisobutyric acid uptake through the cell membranes were less affected. Exposure of the tissue to buffer containing dimethylsulfoxide (Me₂SO) in concentrations of 10 to 20% ($\text{v}\text{v}$) resulted in a stimulatory effect on metabolism. At higher concentrations, Me₂SO was toxic resulting in damaging effects on protein and DNA synthesis as well as on membrane integrity. The stimulatory effects of exposure to low concentrations of Me₂SO on protein and DNA synthesis in kidney slices were concluded to be the result of an increased transport of precursors through the cell membranes.     

Hormonal regulation of postnatal development of renal tubular transport processes

Renal tubular transport of p-aminohippurate (PAH) is immature at birth. Repeated saturation of transport sites by treatment with various organic anions is without any influence on the postnatal development of kidney transport capacity. Hormonal regulation of postnatal maturation of PAH transport must therefore be taken into consideration. It was tried to stimulate immature PAH transport by treating rats of different ages with thyroid hormones, corticosteroids or testosterone, respectively. In rats with immature kidney function, renal PAH excretion can be stimulated by daily treatment with thyroid hormones. Experiments on renal cortical slices have shown that PAH excretion is preferentially stimulated by an increase of transport capacity. Whereas thyroid hormones stimulate the renal excretion of PAH both in young and in adult rats, dexamethasone treatment is more effective in rats with immature kidney function. Dexamethasone treatment is without any influence on PAH accumulation in renal cortical slices. Kidney weight and the protein content of kidney tissue was increased after dexamethasone treatment. Repeated testosterone administration did not stimulate the PAH transport in rats of different ages. The data have demonstrated the influence of thyroid hormones or of dexamethasone on renal tubular transport processes in rats with immature kidney function. Treatment with such hormones could be useful in the management of renal insufficiency in full-term and pre-term neonates with immature kidney function.     

Transport of threonine and tryptophan by rat brain slices: relation to other amino acids at concentrations found in plasma

Threonine content of brain decreases in young rats fed a threonine-limiting, low protein diet containing a supplement of small neutral amino acids (serine, glycine and alanine), which are competitors of threonine transport in other systems (Tews et al., 1977). Threonine transport by brain slices was inhibited more by a complex amino acid mixture resembling plasma from rats fed the small neutral amino acid supplement than by mixtures resembling plasma from control rats or from rats fed a supplement of large neutral amino acids. Greater inhibition was seen with mixtures containing only the small neutral amino acids than with mixtures containing only large neutral amino acids. On an equimolar basis, serine and alanine were the most inhibitory; large neutrals were moderately so; and glycine and lysine were without effect. Threonine transport was also strongly inhibited by α-amino-n-butyric acid and homoserine, less so by α-aminoisobutyric acid, and not at all by GABA. The complex amino acid mixtures strongly inhibited α-aminoisobutyric acid transport by brain or liver slices but, in contrast to effects in brain, the extent of the inhibition in liver was not much affected by altering the composition of the mixture. Tryptophan accumulation by brain slices was effectively inhibited by other large neutral amino acids in physiologically occurring concentrations. Threonine, or a mixture of serine, glycine and alanine only slightly inhibited tryptophan uptake; basic amino acids were without effect and histidine stimulated tryptophan transport slightly. These results support the conclusion that a diet-induced decrease in the concentration in brain of a specific amino acid may be related to increased inhibition of its transport into brain by increases in the concentrations of transport-related, plasma amino acids.     

黄鳝的泌尿系统及其功能

黄鳝腹腔左侧有盲端的中空管状结构,不是退化性腺,而是十分特化的长管囊膀胱。膀胱内壁具大量发达的绒毛,绒毛表面是移行上皮。在绒毛内部或基部有丰富的血管,因此该管囊膀胱不仅可贮存尿液,而且可能对水分等有重吸收作用。在中肾管与膀胱相接处,膀胱腔背侧出现一条明显的纵行皱襞,即在其横切面上观为巨绒毛。巨绒毛形成的原因,主要是中肾管移入膀胱壁所致。中肾管在巨绒毛内移行一程后才开口于膀胱。因此,黄鳝的生殖腺不是一对,而是一个,位于腹腔右侧。黄鳝肾脏细长,呈“丫”,在腹腔背侧,紧贴脊椎。前端为头肾,无肾单位,仅是造血器官。中肾有类似于哺乳类的肾小体,但数量较少,主要分布在肾脏周缘。肾小管包括颈段、初级近曲小管、次级近曲小管、初级远曲小管和次级远曲小管。两中肾管位于两肾叶腹内侧,其上皮间或是假复层柱状上皮,间或是移行上皮。前者含有许多杯状细胞,并可见到顶浆分泌的现象。中肾的肾小管间组织是大量的红细胞样组织,头肾似具有贮存或释放刚成熟的红细胞的组织结构,因此黄鳝肾脏可能是体内主要的造血器官。     

Metabolic heterogeneity of the proximal and distal kidney tubules

Proximal and distal tubule suspensions were prepared from kidneys of Sprague-Dawley rats by an isolation procedure on a Percoll^R gradient. The marker enzymes alkaline phosphatase (brush border) and hexokinase (cytoplasmic) as well as p-aminohippurate transport capacity, gluconeogenic activity and electron microscopy were used to characterize the two kidney tubule suspensions. The results of this study indicate that cytochrome P-450 is localized to the proximal tubular cells and that the O-deethylation of 7- ethoxycoumarin was higher in the proximal than distal fraction. Both proximal and distal tubules showed glucuronidation and deacetylation capacities and a relatively equal distribution of non-protein sulfhydryls. These studies demonstrate metabolic heterogeneity of the nephron, the proximal tubule being the main site of renal xenobiotic metabolism. Understanding of metabolic heterogeneity of proximal and distal kidney tubules should provide important information regarding cell specific mechanisms of nephrotoxicity.     

Oxygen consumption in the rectal gland of the dogfishScyliorhinus canicula and the effects of cyclic AMP

Summary Oxygen consumption was measured in slices of dogfish (Scyliorhinus canicula) rectal gland tissue and compared with spleen and kidney. Concentrations of dibutyryl cAMP and theophylline that have previously been shown to stimulate secretion from the perfused gland and to produce a large increase in ouabain binding in this tissue, greatly increased oxygen consumption in the rectal gland but were without effect on oxygen consumption in the spleen and the kidney. Addition of theophylline alone increased rectal gland oxygen consumption and no further increase was detected on addition of cAMP at the concentration used (0.05 mmol l^–1).Ouabain (10^–4 M) significantly decreased oxygen consumption in all three tissues studied and completely abolished the increase in oxygen consumption of the rectal gland produced as a result of the addition of cAMP and theophylline.These findings are discussed in relation to the apparent specific effect of cAMP on the rectal gland and its possible mode of action in this tissue.     

鸡肾发生的组织学观察

采用组织学方法和电镜技术,对9个不同发育时期的鸡(Callus domestiaus)胚胎进行了观察.通过对鸡胚胎肾组织发生过程的观察,探讨鸡胚中肾的发生与退化,后肾的发生、分化规律和特点.结果表明,孵育到第16期在中肾前端附近出现一些中肾小泡.孵育到第18期形成中肾小管.孵育到第26期,中肾小管的盲端内陷,原始的肾小囊和肾血管球形成,中肾小管显著伸长并迂回曲折.孵育到第33～37期,体前后部中肾组织均已形成完整的肾单位.第37～46期体前部至后部的中肾组织依次退化.孵育到第26期从泄殖腔附近发出的输尿管芽向生后肾组织侵入生长,生后.肾组织产生许多生后肾小泡.第33期出现肾小囊和肾小管,肾小管伸长并发生折叠,出现集合小管、近端小管和远端小管的形态分化.第37～46期肾小体逐渐发育成熟,肾小管继续分化出现细段.鸡的中肾具有排泄功能.鸡后肾的发生与分化存在明显的时间差异.肾单位的分化中,同一胚龄肾组织内可存在不同发育阶段的肾小体,集合小管分化较早,诱导近端小管和远端小管分化,细段分化较迟.     

Acclimation of photosynthesis in Zea mays to low water potentials involves alterations in protoplast volume reduction

Effects of water-stress treatment of Zea mays L. plants on protoplast volume and photosynthesis in leaf slices exposed to solutions of different osmotic potential ( _s) were studied. Decreased photosynthetic capacity in the leaf slices at low tissue _w was associated with dehydration-induced protoplast-volume reduction. Leaf slices from plants exposed to in-situ water deficits exhibited greater photosynthetic capacity and relative protoplast volume at low water potential ( _w) invitro than tissue from control plants.In-situ water stress induced osmotic adjustment of the leaf tissue as determined by pressure/volume analysis. It is concluded that plant acclimation to low leaf _w may involve a reduced degree of cell shrinkage at a given _w. This acclimation would allow for the maintenance of relatively higher photosynthetic capacity at low water protentials.Symbols _s Osmotic potential - _w water potential New Jersey Agricultural Experiment Station Publication No. 12149-6-87     

Metabolic depression during aestivation in Cyclorana alboguttata

The green striped burrowing frog, Cyclorana alboguttata, spends, on average, nine to ten months of every year in aestivation. Recently, C. alboguttata has been the focus of much investigation regarding the physiological processes involved in aestivation, yet our understanding of this frog's capacity to metabolically depress remains limited. This study aimed to extend our current knowledge of metabolic depression during aestivation in C. alboguttata. C. alboguttata reduced whole animal metabolism by 82% within 5 weeks of aestivation. The effects of aestivation on mass specific in vitro tissue metabolic rate (VO₂) varied among individual organs, with muscle and liver slices showing significant reductions in metabolism; kidney VO₂ was elevated and there was no change in the VO₂ of small intestine tissue slices. Organ size was also affected by aestivation, with significant reductions in the mass of all tissues, except the gastrocnemius. These reductions in organ size, combined with changes in mass specific VO₂ of tissue slices, resulted in further energy savings to aestivating animals. This study shows that C. alboguttata is capable of selectively down- or up-regulating individual tissues, using both changes in metabolic rate and morphology. This strategy allows maximal energy savings during aestivation without compromising organ functionality and survival at arousal.     

Odd-skipped related 1 is required for development of the metanephric kidney and regulates formation and differentiation of kidney precursor cells

Formation of kidney tissue requires the generation of kidney precursor cells and their subsequent differentiation into nephrons, the functional filtration unit of the kidney. Here we report that the gene odd-skipped related 1 (Odd1) plays an important role in both these processes. Odd1 is the earliest known marker of the intermediate mesoderm, the precursor to all kidney tissue. It is localized to mesenchymal precursors within the mesonephric and metanephric kidney and is subsequently downregulated upon tubule differentiation. Mice lacking Odd1 do not form metanephric mesenchyme, and do not express several other factors required for metanephric kidney formation, including Eya1, Six2, Pax2, Sall1 and Gdnf. In transient ectopic expression experiments in the chick embryo, Odd1 can promote expression of the mesonephric precursor markers Pax2 and Lim1. Finally, persistent expression of Odd1 in chick mesonephric precursor cells inhibits differentiation of these precursors into kidney tubules. These data indicate that Odd1 plays an important role in establishing kidney precursor cells, and in regulating their differentiation into kidney tubular tissue.     

On the Production and Disposition of Quinolinic Acid in Rat Brain and Liver Slices

Abstract: The de novo production and subsequent disposition of the endogenous excitotoxin quinolinic acid (QUIN) was investigated in vitro in tissue slices from rat brain and liver. Incubation of tissue with QUIN's immediate bioprecursor 3-hydroxyanthranilic acid (3-HANA) in oxygenated Krebs-Ringer buffer yielded measurable amounts of QUIN both in the tissue and in the incubation medium. Saturation was reached between 16 and 64 μM 3-HANA (166 pmol of QUIN formed per milligram of protein after a 60-min incubation with 64 μM 3-HANA). In the brain, more QUIN was recovered from the tissue than from the incubation medium at all time points examined (5 min to 4 h). In contrast, the tissue-to-medium ratio for QUIN in parallel experiments with hepatic slices was ? 1. The disposition of newly synthesized QUIN was further elaborated in tissue slices that had been preincubated for 60 min with 64 μM 3-HANA. Subsequent incubation of brain tissue in fresh buffer revealed a steady but relatively slow efflux of QUIN from the cellular compartment, with >30% remaining in the tissue after a 90-min incubation. Analogous experiments with liver slices showed that >93% of newly synthesized QUIN had entered the extracellular compartment within 30 min. Striatal and nigral slices obtained 7 days after an intrastriatal ibotenic acid injection showed severalfold increases in QUIN production compared with control tissues, in all likelihood due to astrogliosis and associated large increases in 3-hydroxyanthranilic acid oxygenase activity. In addition, the apparent tissue-to-medium ratio was markedly reduced in striatal slices from lesioned animals. Taken together, these data indicate that both brain and liver cells have a rather limited capacity to retain QUIN, and that 3-hydroxyanthranilic acid oxygenase activity is a critical determinant controlling extracellular QUIN concentrations in both organs. Changes in the activity of QUIN's biosynthetic enzyme in the brain can therefore be expected to influence the possible function of QUIN as an endogenous agonist at the N-methyl-D-aspartate receptor in health and disease.     

Control of canine kidney cortex slice volume and ion distribution at hypothermia by impermeable anions

Hypothermia induces swelling of dog kidney cortex slices. Swelling of cells during hypothermia is related to a number of factors including the permeability of Cl⁻. By substituting lactobionate for Cl⁻, while maintaining isoosmotic conditions, swelling is prevented. Lactobionate is an impermeable anion and its presence in the suspending fluid prevents swelling of dog kidney cortex slices in salts of Na⁺, K⁺ or combinations of Na⁺ and K⁺ even in the presence of metabolic inhibitors. By maintaining a ratio of 80 mM lactobionate: 60 mM chloride and an appropriate ratio of Na⁺:K⁺ (80 mM:60 mM), both the total tissue H₂O and ratio of intracellular K⁺/Na⁺ are kept within normal ranges during hypothermic incubation of tissue slices. Kidney cortex slices suspended in this medium at 30 °C respire at a rate 30–40% slower than that of control slices suspended in saline. A similar result is obtained by adding ouabain to slices suspended in saline. This suggests that the Na⁺-pump activity is suppressed under these conditions and results in a reduced energy demand on the cell. These results are discussed in relation to utilizing this type of solution for long-term perfusion preservation of kidneys for transplantation.     

Development and other characteristics of α-methyl-d-glucoside transport by rat kidney cortex slices

α-Methyl-d-glucoside has been shown to be a non-metabolizable sugar which is accumulated against a concentration gradient by a Na⁺-dependent and phlorizin inhibited process by adult rat renal cortical slices incubatedin vitro at 37 °C. (2) The velocity of accumulation increased linearly with substrate concentrations up to 1.5 mM, but at higher concentrations obeyed saturable kinetics with an apparentK_m of about 6 mM. (3) Uptake was enhanced as Na⁺ was increased from 0 to 100 mequiv/l. Higher Na⁺ concentrations caused no further effect. (4) A pH maximum of transport occurred between 7.35 and 8.0. (5) Glucoside uptake was inhibited byd-glucose,d-galactose,d-fructose,d-mannose andd-ribose. The inhibition byd-glucose andd-galactose was competitive with apparentK_t of 24 and 53 mM, respectively. (6) Bothd-glucose andd-galactose accelerated the efflux of α-methyl-d-glucoside from preloaded cells. (7) Kidney cortex slices from 1-day-old rats were unable to accumulate α-methyl-d-glucoside to form a concentration gradient. The ability to concentrate the glucoside increased progressively after birth, reaching near normal in tissue from 15-day-old animals. The data indicate that the transport process in the newborn is rudimentary, failing also to display accelerated efflux phenomenon. (8) α-Methyl-d-glucoside is transported in rat kidney cortex by a mechanism similar in many ways to that ofd-galactose.     

Inhibition by cyclic AMP and dibutyryl cyclic AMP of transport of organic acids in kidney cortex.

1. Cyclic adenosine 3',5'-monophosphate and N-6-2'-O-dibutyryl cyclic adenosine 3',5'-monophosphate decrease the initial entry rate and the steady-state uptake of p-aminohippurate and uric acid by rabbit kidney cortex slices. 2. N-6-2'-O-Dibutyryl adenosine 3'-5'-monophosphate inhibits the tubular transport of p-aminohippurate competitively. 3. Isoproterenol, known to increase cyclic nucleotide concentration of the cortical tubules by activation of adenyl cyclase, decreases p-aminohippurate transport. Antidiuretic hormone which is known to stimulate only medullary adenyl cyclase has no effect on p-amino-hippurate uptake by cortical slices. 4. Theophylline, which inhibits cyclic nucleotide phosphodiesterase and, therefore, enhances the cellular accumulation of endogenous cyclic nucleotide, depresses p-aminohippurate transport.