Urine concentrations in the spaces of the sheep renal pelvis

Transcription

1 Urine concentrations in the spaces of the sheep renal pelvis S Faix, M Szanyiova, L Leng To cite this version: S Faix, M Szanyiova, L Leng. Urine concentrations in the spaces of the sheep renal pelvis. Veterinary Research, BioMed Central, 1996, 27 (2), pp <hal > HAL Id: hal Submitted on 1 Jan 1996 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2 Short note Urine concentrations in the spaces of the sheep renal pelvis S Faix M Szanyiova L Leng Institute of Animal Physiology, Slovak Academy of Sciences, Soltesova 4-6, Kosice, Slovak Republic (Received 25 August 1995; accepted 19 December 1995) Summary&horbar; Urine concentrations were measured in samples from the ureter, the pelvic cavity, close to the tip of the papilla, and from the most proximal part of the fornices of sheep kidneys. It was found that the concentration of urea, the osmolality, and the urine-to-plasma ratios of inulin, urea and the osmolality were higher in the ureter than in the pelvic cavity. The same parameters were found to be higher in the pelvic cavity than in the fornices except for the urea concentration which was unchanged. The results of this study revealed the various concentrations of urine in the ureter, the pelvic cavity and the proximal part of fornices of sheep kidney. sheep / kidney / renal pelvis / urine concentration Résumé &horbar; Les concentrations urinaires dans les espaces du pelvis rénal chez le mouton. Les concentrations urinaires ont été mesurées dans des échantillons prélevés au niveau de l uretère, de la cavité pyélique (près de la papille) et de la partie la plus proximale des fornix du rein de mouton. La concentration de l urée, et l osmolalité étaient plus élevées dans l uretère que dans la cavité pyélique. Les mêmes paramètres se sont avérés plus élevés dans la cavité pyélique que dans les fornix, à l exception de la concentration de l urée qui n était pas différente. Ces résultats mettent en évidence les différences de concentration urinaire au niveau de l uretère, de la cavité pyélique et de la partie proximale des fornix du rein chez le mouton. mouton / rein Ipelvis rénal/concentration urinaire * Correspondence and reprints

3 INTRODUCTION The accumulation of urea in the papilla is closely related to the amount of contact between the pelvic urine and the renal papilla (Gerz et al, 1966). The renal papilla of a rat kidney rapidly lose urea and the osmolality there decreases when the pelvis is opened and the papilla are no longer bathed in urine (Chuang et al, 1978). Since the time of these works interest in the role of the renal pelvis in the urinary concentrating mechanism has gradually increased. Recently reported findings of urea reabsorption from the renal pelvis of sheep suggest a considerable recycling of osmotically active substances between the pelvic urine and the medulla (Cirio and Boivin, 1990). In this study we wanted to determine the concentrations of urine in samples from the ureter, in the urine from the pelvic cavity that surrounds the tip of a papilla and in the urine from the most proximal part of the pelvic fornices which are adjacent to the outer medulla of the sheep kidney. MATERIALS AND METHODS Six Merino ewes, weighing from 22 to 26 kg were studied. The animals were fed hay ad libitum and they had free access to water and minerals. Anaesthesia was induced with an intravenous injection of pentobarbital and then maintained with halothane in oxygen. A closed circuit device for the anaesthesia was connected to the animals by an endotracheal tube. The blood presure was measured through a catheter placed in the left carotid artery. The mean arterial pressure was kept within the stable range of kpa (75-95 mmhg). The left saphena vein was used for an infusion of inulin. The solution of inulin consisted of pyrogen-free inulin (Serva) dissolved in a sterile 0.15 M NaCI. The prime dose of inulin solution (5 g/50 ml) was injected into the jugular vein and then continuous infusion (27.1 mg/ 6.5 ml/min) was initiated. In order to ensure an adequate distribution of inulin in extracellular space the first collection period began 60 min after starting the continuous infusion of inulin. Body temperature (38.5 C) was maintained by an electric under-blanket controlled by a rectal thermometer. After the laparotomy, the left kidney, renal pedicle and ureter were gently separated from the peritoneal membranes and the fat. The kidney was carefully mounted in a plastic cup to avoid constriction of the renal vessels. A glass microcapillary (Curtin Matheson Scientific, Inc, USA) with an outer diameter 1.4 mm, inner diameter 1.0 mm and length 60 mm was placed in the ureter across a small incision of the ureter near the renal hillus. A thin polyethylene (PE) microcannula with an outer diameter 0.9 mm, inner diameter 0.8 mm, total length 150 mm and with tip inner diameter mm was then introduced into the glass microcapillary and samples of urine were collected for 5 min. To avoid the different effects of capillarity, the same PE microcannula was used for the entire experiment within a given kidney. The glass microcapillary with PE microcannula was then pushed into the renal pelvis cavity and samples of urine were collected again for 5 min. The samples of urine from the fornices were collected after the polyethylene microcannula was pushed into the fornix of the renal pelvis as far as possible. The depth of insertion of the cannula was controlled through comparison with a second cannula placed on the kidney surface. The position of the tip of internal cannula was also examined after the experiment by the dissection of the kidney. The samples of urine were collected five times from each part of the urinary space. The intervals between the collection period of each sample were 10 min. In this experimental design, the bathing of papilla with urine was not interrupted and urine could flow out only through the PE microcannula. Blood was collected from the left carotid artery. Inulin in both the plasma and urine were determined by the fluorometric methods of Vurek and Pegram (1966). Urea was analysed by the fluorometric method of Leng et al (1986). Osmolality was measured cryoscopically on a Knauer osmometer. The results are presented as means ± SEM. Statistical significance was evaluated by paired t-test. RESULTS The data measured in the different urinary spaces of the sheep kidney are summa-

4 rized in table 1. The urea concentration and osmolality were significantly higher in the ureter than in the pelvic cavity. At the same time the urine osmolality in the samples from the pelvic cavity were found to be significantly higher than in the fornices while the differences in urea concentration were not significant. Likewise the highest values for urine-to-plasma ratios of inulin, urea and osmolality were determined in the ureter and the lowest ones in the fornices with all these differences being significant. The differences in the fractional urea delivery, referring to the fractions of filtered urea reaching the place of sample collection, were not significant. The urine flow rate measured in contralateral kidneys was stable throughout the whole experiment (0.54 ± 0.14 ml-min-1). DISCUSSION It appeared that the renal pelvis plays an important role in the final concentrating of urine. Our results demonstrated differences in the values of the concentrations of urea, inulin and osmolality between the samples from the two parts of urinary spaces of the kidney (pelvic cavity and fornices) and from the ureter. The findings of lowest concentrations of urea and osmolality in urine of the fornix could be explained by diffusion of solutes via thin pelvic epithelium to surrounding tissue of the outer medulla or by water efflux from the tissue. The reduced inulin urine-to-plasma ratio in the urine of fornix indicates, rather, water leak from the outer medullary tissue. This is supported by the fact that the papilla and urine flowing out of Bellini ducts are known to have considerably higher osmolality than the outer medulla. Our experimental approach allowed the continuous bathing of the papilla with urine in such a way that the concentrating ability of the kidneys was conserved. Urine could only flow out through a microcapillary with a constant resistance. Knepper and Stephenson (1986) found that the final urine osmolality was the same as the osmolality of the core or interstitium at the papillary tip in rats. Unfortunately, the Bellini ducts of the sheep crest kidney are not available to micropuncture or microcatheterization due to their anatomical structure. The results presented here suggest that the urine flowing out of the sheep Bellini

5 ducts does not have the same concentration as the final urine in the ureter. It appears that urine flowing out from the Bellini ducts is modified by exchange processes through the epithelium which covers the sheep renal pelvis. Ruminants are known to have specially well-developed fornices in the renal pelvis reaching the outer medulla, the tissue zone with a lower osmolality as was found in the papilla (Pfeiffer, 1968). In conclusion, the demonstrated various concentrations of urine in the ureter, the pelvic cavity and the proximal part of fornices suggest a considerable ability of the sheep renal pelvis to modify the final urine concentration. ACKNOWLEDGMENT This study was supported by the Granting Agency for Science of the Slovak Republic, Grant 1322/95. REFERENCES Chuang EL, Reineck HJ, Osgood RW, Kunau RT Jr, Stein JH (1978) Studies on the mechanism of reduced urinary osmolality after exposure of the renal papilla. J Clin Invest 61, Cirio A, Boivin R (1990) Urea recycling from the renal pelvis in sheep: a study with 14 C-urea. Am J Physiol 258, F1196-F1202 Gerz KH, Schmidt-Nielsen B, Pagel D (1966) Exchange of water, urea and salt between the mammalian renal papilla and the surrounding urine. Fed Proc 25, 327 Knepper MA, Stephenson JL (1986) Urinary concentrating and diluting processes. In: PhysiologyofMembrane Disorders, 2nd edn (TE Andreoli, DD Fanestil, JF Hoffman, SG Schultz, eds), Plenum, New York, Leng L, Szanyiova M, Faix S, Varady J, Boda K (1986) Simple fluorometric ultramicroassay for urea in tubular fluid of the kidney. Pflbgers Arch Eur J Physiol 406, Pfeiffer EW (1968) Comparative anatomical observations of the mammalian renal pelvis and medulla. JAnat102, Vurek G, Pegram S (1966) Fluorometric method for the determination of nanogram quantities of inulin. Anal Biochem 16,