H. R. Ulfendahl

Hydrostatic pressures within the vascular structures of the rat kidney

SummaryThe pressure conditions at the distal end of the interlobular arteries and in the interlobular veins were investigated from the pressures obtained in superficial small arteries and veins, accidentally found on the kidney surface, during the subsequent blockade of the blood stream in the down-stream and up-stream direction, respectively.The results suggested a hydrostatic pressure in the distal end of the interlobular arteries of about 85 mm Hg under normotensive conditions-a pressure which remained fairly constant when the perfusion pressure in the renal artery was decreased within the autoregulation range. The results indicate a considerable pressure drop of about 40 mm Hg along the interlobular arteries. During hypotension this pressure drop decreased, implying a decreased resistance in the interlobular arteries, i.e.a typical autoregulative response.The pressure in the interlobular veins amounted to about 5 mm Hg, which is a few mm Hg higher than that in the renal vein and about 7 mm lower than that in the peritubular capillary network. The results suggest a flow resistance located somewhere between the peritubular capillaries and the intrarenal veins. This resistance is not influenced by vasoactive substances but it is decreased when the systemic venous pressure is raised above 10 mm Hg. The resistance seems to act in the direction of protecting the peritubular capillaries from minor changes in the central venous pressure.

Intrarenal oxygen tension measured by a modified Clark electrode at normal and low blood pressure and after injection of x-ray contrast media

Abstract The oxygen tension (pO2) in the rat kidney was studied using a Clark microelectrode with a guard cathode behind the sensing cathode. The mean (± SEM) outer tip diameter of the electrodes used was 5.5 ± 1.9 μm. The zero-pO2 current amounted to 12.5 ± 0.9 pA at 37°C; at air saturation it was 252 ± 22.9 pA. Rats with a systolic blood pressure (BP) above 80 mmHg (where 1 mmHg = 133 Pa) showed an average pO2 in the cortex of 45 ± 2 mmHg and in the outer medulla of 31 ±1 mmHg. In rats with a BP below 80 mmHg a paradoxically high outer medullary pO2 of 40 ± 4 mmHg was found, while the pO2 in the cortex was 27 ± 4 mmHg. Changes in pO2 were also noted in the renal cortex and outer medulla after intravenous injections of the x-ray contrast medium diatrizoate (370 mg iodine/ml). In rats with normal BP, injection of diatrizoate caused a slight fall in pO2 in the renal cortex, from 42 ± 4 to 38 ±4 mmHg. In the medulla pO2 decreased significantly from 34 ± 6 to 20 ±4 mmHg. Ringer’s solution did not induce any changes.

Effect of intravenous contrast media on proximal and distal tubular hydrostatic pressure in the rat kidney.

The effect of i.v. injection of contrast media (CM, 1 600 mg I/kg b.w.) on proximal and distal tubular hydrostatic pressure (PTHP, DTHP) in the rat was investigated using a micropuncture technique. The PTHP and DTHP after injection of diatrizoate, iohexol, ioxaglate, or mannitol returned to control values within approximately 20 min. However, following iotrolan injection PTHP was still elevated above control levels after 35 min while DTHP remained elevated throughout the experiment (50 min). Iotrolan has a lower osmotic potential than the other CM when given in equivalent iodine doses. The concentration of iotrolan may thus increase more along the tubules than the other CM and consequently lead to a higher viscosity of urine, resulting in increases in PTHP and DTHP. The high intratubular pressure induced by iotrolan may explain our previous findings of reduced single nephron glomerular filtration rate caused by this CM.

Hydrostatic pressure in the subcapsular interstitial space of rat and dog kidneys

SummaryExperiments were performed in rats and dogs in order to reevaluate the concept of a high renal interstitial pressure. Assuming that the renal subcapsular pressure represents the pressure 2 of the superficial interstitium, catheters were implanted in the subcapsular space and the pressure was continuously recorded with a transducer of a very low volume displacement. In 17 rats a mean subcapsular pressure of 3.8 cm H2O±2.0 was measured, while 6 dogs had an average subcapsular pressure of 10.8 cm H2O±3.0. The subcapsular pressure was found to increase during renal venous constriction and ureteral pressure elevation, procedures which are very likely to lead to a rising renal interstitial pressure.To demonstrate a functional communication between the subcapsular and the deep renal interstitium I131-labelled albumin was injected into the subcapsular space of 5 rats, while the hilar lymph was collected through a cannulated lymph vessel. It was found that already in the first collection period of 20 min duration a considerable I131 activity was present in the lymph which consisted mainly of albumin-bound iodide. It is concluded that the low subcapsular pressure is probably valid for the entire renal interstitial compartment.

Iodine concentrations in the rat kidney measured by x-ray microanalysis Comparison of concentrations and viscosities in the proximal tubules and renal pelvis after intravenous injections of contrast media

Purpose: To measure the iodine concentrations in the proximal tubules and renal pelvis after i.v. injections of contrast media (CM) at 1600 mg I/kg b.w., using a micro-puncture technique and X-ray microanalysis Material and Methods: The correlation between the viscosity of each CM and its iodine concentration was evaluated and the viscosity of the fluid in the proximal tubule and renal pelvis was estimated in rats Results: After iotrolan injection, the iodine concentration in the proximal tubular fluid had increased to values about three times higher than those reached with diatrizoate, iohexol and ioxaglate. Similarly, iotrolan tended to produce a higher iodine concentration in the renal pelvis than did the other CM. the urine viscosity in the renal pelvis was much higher after the iotrolan injection than after the other CM injections Conclusion: High urine viscosity after iotrolan injection can at least partly explain our previous findings of a prolonged increase in tubular hydrostatic pressure and a prolonged decrease in the single nephron glomerular filtration rate after administration of this CM

Colloid osmotic pressure of the subcapsular interstitial fluid of rat kidneys during hydropenia and volume expansion

SummaryTo determine the colloid osmotic pressure of subcapsular interstitial fluid in rat kidneys two different methods were used. Collection of subcapsular fluid with glass pipettes or implanted microcatheters and subsequent protein analysis resulted in a protein concentration of 1.8g%±0.6 and 2.0g%±0.8, respectively. Lymph protein concentration was not significantly different from that of subcapsular fluid samples. During extracellular volume expansion both subcapsular and lymph protein concentration fell to 0.42g%±0.23 and 0.7g%±0.5. Application of anin vivo oncometric method resulted in an effective oncotic pressure about twice that estimated from protein determinations. Using average values for intratubular and intracapillary oncotic and hydrostatic pressures a tubulo-interstitial net driving force of 20 mm Hg and an interstitial-capillary net driving force of 13 mm Hg is estimated in hydropenic animals. During volume expansion net transtubular pressure gradient is reduced to about 60–70% of control while the transcapillary gradient is virtually unchanged.

An integrating flame photometer for simultaneous microanalysis of sodium and potassium in biological fluids

Abstract A detailed description is given of a low-cost integrating flame photometer for simultaneous analysis of sodium and potassium. The construction is simple and high sensitivity is achieved without the use of photomultiplier tubes. Undiluted samples of volumes down to 10 −10 liter, containing a minimal amount of 10 −13 mole of potassium and 0.5 × 10 −12 mole of sodium have been analyzed. The sensitivity of the sodium channel can easily be increased. Analysis of 3 × 10 −10 mole of sodium gave a coefficient of variation of ±1.7% and analysis of 10 −11 mole of potassium gave one of ±3.3%. The effects of adding various substances to the samples have been tested. It is shown that different anions may change the results but that this error may be reduced by addition of an optimal amount of ammonium phosphate to the sample. Some organic substances were tested and had in general no effect on the results, as confirmed by analysis of urine. High concentrations of albumin, however, increased slightly the amount of emitted light in the potassium analysis.

Effect of furosemide or mannitol before injection of a non-ionic contrast medium on intrarenal oxygen tension.

Oxygen tension (pO2) in rat renal cortex and outer medulla was studied after an intravenous injection of mannitol or furosemide, followed 10 minutes later by an intravenous injection of the non-ionic X-ray contrast medium (CM) iopromide (370 mg iodine/ml). Ten minutes after mannitol injection, before injection of CM, pO2 in the medulla had decreased from a control level of 32 +/- 3 to 28 +/- 4 mm Hg. The addition of CM caused a further decrease, to 24 +/- 5 mm Hg, which was a significant reduction. Ten minutes after furosemide injection the pO2 in the medulla had increased significantly, from a control value of 32 +/- 2 to 44 +/- 4 mm Hg. Injection of CM caused a significant decrease in pO2 to 37 +/- 3 mm. Ringers solution (n = 6) caused no changes. We conclude that pretreatment with mannitol or furosemide does not prevent the CM-induced decrease in pO2 in the outer medulla.

Effects of High- and Low-Osmolar Contrast Media on Renal Plasma Flow and Glomerular Filtration Rate in Euvolaemic and Dehydrated Rats: A Comparison between Ioxithalamate, Iopamidol, Iohexol and Ioxaglate

The effects of a slow intravenous injection of contrast media (CM) on renal function and haemodynamics were investigated in euvolaemic and dehydrated rats. Iodine-equivalent doses (1600 mg I/kg body weight) of ioxithalamate, ioxaglate, iopamidol and iohexol were used. Glomerular filtration rate (GFR) and renal plasma flow (RPF) were assessed with clearance techniques. In euvolaemic rats no statistically significant decrease in GFR or RPF was found after CM injections. In the dehydrated rats the changes in GFR were more pronounced and this was significantly decreased in the ioxithalamate and iopamidol groups while RPF was still not decreased. This study indicates that dehydration potentiates adverse effects of CM on GFR and that there may be differences between the effects of low-osmolar and high-osmolar CM on GFR and also between different low-osmolar CM.

Microphotometry utilizing a shrinking droplet technique

Abstract A method for spectrophotometric determinations in the submicrogram range is described. By means of a shrinking droplet technique the optical density of small volumes was increased up to 300 times. The samples were shrunk in a Teflon cup by exposure to heated air. Measurements of the diameters of the small spheres formed, when oil was added, made it possible to calculate the volume reduction. The optical density of the sample was measured in a microscope photometer—either directly with the spherical droplets still remaining in the transparent Teflon cup or, with higher precision, after transfer of the sample to a hemocytometer cuvet sealed with oil.