摘要:

Although only 10-15% of renal blood flow enters the medulla, renal medullary hemodynamics have been implicated as a key factor for the ability of the kidney to excrete concentrated or diluted urine and to be involved in sodium homeostasis. Due to the obvious importance of medullary hemodynamics, several methods have been developed or modified for estimating regional renal blood flow. The aim of the present paper is to evaluate critically the most commonly used methods available today. Those which are considered in this paper are: (1) albumin accumulation (Lilienfield), (2) rubidium-86 uptake, (3) transit time-indicator dilution, (4) red cell velocity tracking, (5) red cell flux (fluorescently labeled red cells) and (6) laser-Doppler flowmetry. Depending on the method of choice, the reported control values for renal medullary blood flow differ up to tenfold. Overall, it appears that the discrepancies in values obtained from the different methods will not be resolved until the methods are compared directly in the same animal and during different experimental conditions. Furthermore, one needs to understand and describe accurately the involved errors so that proper corrections can be made. It seems likely, however, that the majority of the techniques can be used to study relative changes, but attempts should not be made to draw conclusions about the absolute flow value. In this regard the laser-Doppler method seems to be superior in its simplicity of use and its large advantage of continuous and relatively noninvasive measurement.

ISSN:1420-4096    

DOI:10.1159/000173457

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

Angiotensin II (Ang II) receptor subtypes in the rat kidney were investigated by using type 1 (AT1) and type 2 (AT2) Ang II receptor antagonists to discriminate specific 125I-[Sar1, Ile8] Ang II binding sites with in vitro autoradiography. DuP 753, a nonpeptide Ang II antagonist specific for the AT1 sites, potently displaced binding in glomeruli (Ki = 23.9 ± 3.3 nM) and proximal tubules (Ki = 43.4 ± 17 nM). By contrast, the AT2 antagonists, PD 123177 and CGP 42112A, were very weak in competing for specific 125I-[Sar1, Ile8] Ang II binding sites. AT1 receptors, as determined in the presence of an excess concentration (10 μM) of the AT2 antagonist, PD 123177, account for 95% of total renal Ang II receptors, whereas AT2 receptors, as determined in the presence of an excess concentration (10 μM) of the AT1 antagonist, DuP 753, represent approximately 5% of total 0renal Ang II receptors. In addition, the reducing agent, dithiothreitol, produces a dose-dependent inhibition of Ang II receptor binding with an IC50 of 2 mM, a characteristic of the AT1 receptors. These findings indicate that the AT1 receptor is the predominant subtype at multiple anatomical sites in the rat kidney.

ISSN:1420-4096    

DOI:10.1159/000173458

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

A method for the separation and quantitation of multiple forms of active renin in human plasma is described. Shallow gradient isoelectric focusing of plasma resolved active renin into seven distinct components in each of 10 healthy normal individuals. Plasma renin activity focused at isoelectric points of 5.71,5.57,5.47,5.22,5.08,4.93, and 4.82 with corresponding proportions of 16.3, 15.4, 21.1, 20.3, 14.0, 10.0, and 2.5%. Silicon dioxide treatment of plasma significantly increased the yield of renin in the focusing gels. Although each individual plasma sample contained the same seven renin forms, there was variability in the relative proportions of the multiple renin forms between individuals. This variance was significantly greater than the variance introduced by the determination itself. The same seven active renin forms were also present in human renal cortical tissue. In conclusion, a method for the determination of multiple renin forms in plasma and renal cortical tissue is presented. At least seven active multiple renin forms were resolved in human plasma and renal cortex.

ISSN:1420-4096    

DOI:10.1159/000173459

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

The glomerular permeability of the isolated perfused kidney is manifold higher than in vivo, although structural changes at the glomerular filtration barrier are not described. It has been proposed that in vivo high molecular weight plasma proteins are concentrated at the glomerular endothelium forming an additional filtration barrier (‘concentration polarization’). To test this hypothesis, isolated rat kidneys were perfused with substrate-enriched Krebs-Henseleit solutions containing albumin (50 g/l) or albumin/globulin (40/10 g/l), or with plasma. The pO2 was 675 mm Hg. Furthermore experiments were carried out with the addition of erythrocytes with and without a reduced 02 supply (pO2 35 mmHg). Independent of the composition of the perfusate a continuously increasing glomerular permeability was observed immediately after perfusion was started. After about 10 min, a steady state value for the glomerular permeability was reached. The addition of globulin to the perfusate or perfusion with plasma did not prevent the initial increase of the permeability. However, after addition of 5% erythrocytes to the perfusate the increase of permeability was much less pronounced. Neither the reduction of the O2 supply nor the addition of erythrocytes to a higher concentration than 5% had any further effect on the glomerular permeability. These data show that concentration polarization of high molecular weight proteins does not take place at the endothelium of the glomerulus. Independent of their ability to carry O2 erythrocytes play an important role in the glomerular filtration proc

ISSN:1420-4096    

DOI:10.1159/000173460

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

In the late neonatal period of male Wistar rats (10 days old) concentrations in plasma were higher for 5 of 24 amino acids compared to adult animals (2 months old): β-alanine, tyrosine, glycine, histidine, and the dipeptide anserine. The plasma concentrations of tryptophan, valine and leucine were lower in young than in adult rats. The renal clearances of amino acids were lower in young rats, both in relation to 1 g b.w. and related to 1 g kidney weight. In the latter case the differences became more distinct because the relative kidney weight was higher in young than in adult animals (1.17 ± 0.07 vs. 0.82 ± 0.03 g/l00 g b.w.) and significant age differences in renal water content did not exist. The apparently more effective tubular reabsorption capacity in young rats can be explained as follows: Because of the significantly lower GFR in 10-day-old rats compared with adults (0.46 ± 0.03 vs. 1.10 ± 0.09 ml/ min/1 g kidney), the glomerularly filtered load of amino acids is generally lower in young rats (exceptions: tyrosine glycine). Therefore, the amino acid transporting carrier systems are able to reabsorb the absolutely lower amounts of amino acids from the ultrafiltrate in immature animals. This hypothesis is supported if one relates the renal amino acid clearance to the clearance of inulin. In this way it is possible to show that there are absolutely no differences between both age groups indicating mature transport systems for endogenous amino acids as early as in 10-day-old rats. The urinary excretion of amino acids in young and adult animals was less than 1-5% of the filtered load and age differences were not signifi

ISSN:1420-4096    

DOI:10.1159/000173461

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

Repeated adminisatration of triiodothyronine (T3, 20 µg/l00 g b.w., once daily for 3 days) or dexamethasone (60 µg/l00 g b.w., once daily for 3 days) caused significant changes of amino acid plasma concentrations in young (10 days old) and adult rats (2 months old). After treatment with T3, in young animals concentrations of β-alanine, aspartic acid, glutamic acid, ornithine, asparagine, leucine, taurine, serine, alanine, and glutamine were enhanced, whereas those of tyrosine, arginine, and threonine were significantly diminished. In adult rats only slight changes occurred after both T3 and dexamethasone. In the kidney, the reabsorbed fraction of amino acids was enhanced after both T3 and dexamethasone treatment in young rats, whereas in adult rats the two hormones were without influence on tubular reabsorption of amino acids. Taken together, both different plasma concentrations of amino acids and changes in amounts of amino acids reabsorbed in the tubuli, in adult rats the fractional excretion of amino acids was nearly unchanged following hormone treatment (exception: significant increase in taurine clearance). But in young animals the fractional excretion was reduced in 15 of 22 amino acids after dexamethasone and in 12 of 23 amino acids after T3 treatment, indicating stimulatory effects of both hormones on tubular amino acid carrier systems in immature anima

ISSN:1420-4096    

DOI:10.1159/000173462

出版商:S. Karger AG    

年代:1992

数据来源: Karger