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Biomedical subjects

R Greger

Publications and source records attributed to R Greger.

At least 163 records · Page 9Linked to original sources
PubMed1978

Effect of benzolamide on luminal pH in proximal convoluted tubules of the rat kidney.

Luminal pH in early and late proximal tubules was recorded continuously with antimony microelectrodes before and during carbonic anhydrase inhibition. Following i.v. application of benzolamide (25 mumol/kg BW), luminal pH decreased almost immediately in early proximal tubules (deltapH--0.42 +/- 0.06SEM), but increased in late proximal tubules (deltapH +0.27 +/- 0.06). Urinary pH increased (deltapH + 1.6 +/- 0.16) after a delay of some 30 s. Similar results, i.e. decrease of pH in early and increase of pH in late proximal tubules, were obtained, when benzolamide containing solutions were microinfused into early proximal tubules or superfused on the nephron surface. In contrast, luminal pH decreased in late proximal tubules, when benzolamide was microinfused into the same nephron segment. The decrease of luminal pH indicates inhibition of luminally active carbonic anhydrase, leading to delayed buffering of secreted hydrogen ions. The increase of luminal pH in late proximal tubules may be attributed to several factors including increased delivery of bicarbonate, impaired bicarbonate exit at the antiluminal membrane and decreased hydrogen ion formation in the tubular cell due to inhibition of cellular carbonic anhydrase.

Animals↗
PubMed1978

Distal site of calcium reabsorption in the rat nephron.

The site of outflux of 45Ca along the nephron were investigated using microinfusion technique in acutely thyroparathyroidectomized (TPTX), intact and TPTX Wistar rats substituted with parathyroid hormone (PTH). In all three groups 45Ca outflux occurred along the proximal tubule, the loop of Henle and along the distal tubule. After microinfusion into late distal tubules 45Ca recovery in ipsilateral urine was essentially complete for the TPTX group but was only 83 and 65% for the intact and the PTH substituted animals. Increases in microinfusion flow rate from 2--20 nl/min into early and middle distal tubules resulted in increased urinary recovery of 45Ca for all three groups. Similarily, increases in microinfusate Ca concentration from 0.2--2.0 and 5.0 mmol/l resulted in increased fractional urinary recovery of 45Ca both in the presence and absence of PTH. When 45Ca and 3H insulin containing solutions were continuously microinfused into early distal tubules for one hour periods an anticalciuric effect of PTH could be demonstrated. It is concluded that Ca, in addition to its outflux in the proximal tubule and in the loop of Henle, is reabsorbed in the distal tubule accessible to micropuncture. PTH acts anticalciuric at this latter site.

Animals↗
PubMed1978

[Uptake of 2-C14 urate by erythrocytes in hyperuricemia and in gout (author's transl)].

The uptake of 2-C14 urate by erythrocytes was measured in 19 patients with primary hyperuricemia, 6 patients with secondary hyperuricemia, 17 patients with primary gout and 30 controls. The uptake of urate in patients with primary gout was significantly lower than in the controls. In contrast no such difference could be observed in patients with primary and secondary hyperuricemia. The uptake of labeled urate by erythrocytes from gouty patients is especially diminished in the early phase of the uptake kinetics. The possible relevance of this finding for the pathogenesis of urate precipitation in gout is discussed. Further, we consider the application of the tracer urate uptake by erythrocytes as an aid in the early diagnosis of gout.

Erythrocytes↗
PubMed1977

Site of renal phosphate reabsorption. Micropuncture and microinfusion study.

Using modified microinfusion and free flow micropuncture techniques in the same intact and acutely thyroparathyroidectomized (TPTX) Munich-Wistar rats the nephron sites for phosphate reabsorption were reinvestigated. In intact animals, 62% of filtered phosphate was reabsorbed in the proximal tubule but none in the loop of Henle, here defined as the nephron segment between the last accessible proximal and the first distal convolution. Delivery of phosphate to the superficial distal tubule significantly exceeded urinary phosphate excretion but no phosphate reabsorption could be detected in the terminal nephron by distal microinfusions of radioactively labelled phosphate (32P). In TPTX rats, proximal phosphate reabsorption was enhanced and there was marked phosphate reabsorption in the loop of Henle. Similarly, 32P microinfused in the late proximal tubule was almost completely reabsorbed. Again, no phosphate tracer outflux was detected after distal microinfusion. It is concluded that phosphate reabsorption is confined to the proximal tubule and the loop of Henle.

Animals↗
PubMed1977

Stationary microperfusion study of phosphate reabsorption in proximal and distal nephron segments.

Micropuncture studies demonstrate phosphate reabsorption in proximal tubules and between the late proximal and early distal convoluted tubule accessible to micropuncture. To further define the sites of phosphate reabsorption, the stationary microperfusion technique was applied to proximal and distal nephron segments. Phosphate reabsorption was evaluated in superficial loops of proximal tubules, descending segments beyound late proximal tubules accessible to micropuncture, ascending segments up to the point of micropuncture in the distal tubule, and superficial loops of distal tubules of thyroparathyroidectomized rats. Microperfusates of 1.3 or 2.6 nl (100 mmol/1 mannitol, 100 mmol/l NaCL, 32P-phosphate and 3H-inulin) were injected and then withdrawn after contact times of 2--108 s. Phosphate recovery relative to that of inulin was determined. A steep exponential decline of phosphate recovery (R) iwth increasing contact time (t) was observed in the superficial proximal tubule and descending segments. The slopes of the logarithmic regressions (10log R)/t, +/- SEM) were: -1.68 +/- 0.33 and -1.21 +/- 0.24min-1 in superficial proximal tubules and descending segments respectively. In contrast, no significant decline in phosphate recoveries (-0.02 +/- 0.04 and + 0.11 +/- 0.10 min-1) was apparent in the ascending segments and distal tubule. It is concluded that phosphate is reabsorbed in the proximal convoluted tubule and adjacent descending segments of the superficial nephron and that there is no significant phosphate reabsorption in distal convoluted tubules and adjacent ascending segments.

Animals↗
PubMed1977

Factors affecting urate reabsorption in the rat kidney.

1. Urate transport in the rat appears to be saturable. However, affinity of the transport system for urate is very low and transport far from saturated at physiological plasma concentrations. 2. Since increase of the nonionized fraction of uric acid by a factor of five failed to increase urate reabsorption, transport cannot be due to nonionic diffusion but rather involves ionized urate. 3. Increases in luminal flow rate markedly depress urate reabsorption in the loop of Henle, which results in wash out of medullary urate.

Animals↗
PubMed1975

Handling of allantoin by the rat kidney. Clearance and micropuncture data.

Renal excretion of allantoin was measured by tracer techniques. After injection of 2-C14 urate and H3 inulin, clearances of allantoin and inulin were measured and both proximal and distal tubules were micropunctured. In confirmation of earlier results 2-C14 urate injected into an intact animal is very rapidly converted to C14 allantoin: after 15 min more than 90% of urinary tracer is present as allantoin. It was further observed that 1) allantoin clearance is essentially identical with inulin clearance over a wide range of urine flows; 2) no net transport of allantoin occurs in either proximal or distal tubules. Clearly allantoin is handled by the rat kidney like inulin. The total excretion of filtered allantoin unlike that of filtered urate provides an easy and effective mechanisms for animals possessing the enzyme uricase to dispose of their purine loads.

Allantoin↗