M. Wolgast

Blood Flow in the Rabbit Tracheal Mucosa under Normal Conditions and under the Influence of Tracheal Intubation

Isotope la belled microspheres were used to study the capillary blood perfusion of the rabbit tracheal mucosa. Under resting conditions the perfusion was about 0.3 ml/min ® g (i.e. about 60% of the relative cerebral blood flow). Irritation of the tracheal mucosa by an endotracheal tube caused a steep rise in blood flow, tenfold or more. This was probably due to relaxation of the arterioles caused by a release of histamine‐like substances.

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.

Experimental Obstructive Hydronephrosis in Newborn Rats: II. Long-term Effects on Renal Blood Flow Distribution

Partial obstruction of one ureter was created in newborn rats. The weights and blood flows (using the 86Rb-extraction method) of the cortex and outer and inner medulla were examined nine weeks later, i.e., in the adult. The obstructed pelvis was found to be enlarged 7-fold. The whole kidney blood flow on the hydronephrotic side was reduced by 10%; this was compensated by an increase on the contralateral side. There was a tendency to redistribution of flow from the cortex to the outer medulla; no other effects on regional flow were observed. The weight of the hydronephrotic kidneys was the same as that of the kidneys in control rats; hence no apparent atrophy was present. In contrast, the contralateral intact kidney was hypertrophied. The weight distribution of the different regions remained unaltered. Thus, the inner medullary weight was unaffected also on the obstructed side, although it showed considerable deformation. In the discussion, it is proposed that atrophy of the hydronephrotic kidney was probably present, but it was not detected because of the biological variation and the small number of observations. This presumed atrophy was uniform in all the regions and parallel with the reduction of whole kidney blood flow; hence the regional flows were relatively unaffected. It is concluded that unilateral partial obstruction in the newborn rat causes (i) discrete, parallel reductions of hydronephrotic kidney weight and flow, which are (ii) unrelated to the size of the obstructed pelvis and (iii) completely compensated by increases in the contralateral intact kidney.

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.

Extensive tubular secretion and reabsorption of creatinine in humans.

The validity of creatinine as a marker for the glomerular filtration rate was studied in 8 healthy volunteers in different stages of hydration and during large variations in urinary flow rates. The urine flow was 8.4 ml/min in a dehydrated state (due to furosemide infusion; 8 mg/h) and raised to 23.2 ml/min after rapid rehydration. The creatinine to inulin clearance ratio changed considerably from 1.47 in rehydrated state, indicating a substantial tubular secretion of creatinine, to 1.05 in dehydrated state, indicating a reabsorption of creatinine almost equal to secretion. Thus, substantial tubular secretion and reabsorption of creatinine, changing in relative importance in relation to the degree of hydration, make creatinine clearance an unreliable marker for the glomerular filtration rate.

Influence of renal nerve activity on arteriolar resistance, ultrafiltration dynamics and fluid reabsorption

In anaesthetized 300 g rats, the influence of sympathetic nerve activity on the renal hemodynamics, glomerular filtration and fluid reabsorption was studied with direct stimulation at frequencies of 2 Hz and 5 Hz. The single nephron plasma flow at control conditions was 164 nl/min decreasing to 138 nl/min during 2 Hz and 68 nl/min during 5 Hz, reaching complete glomerular ischemia at about 10 Hz. At 2 Hz, the pressure drop over the two arterioles remained essentially unchanged, indicating an equal response to sympathetic discharge. At higher frequencies the afferent tone showed a more marked increase. The glomerular ultrafiltration decreased in parallel to the blood flow. The filtration fraction remained thereby constant at about 0.33. The fractional proximal fluid reabsorption up to the puncture site in early distal tubules showed a clear increase; the Tf/P-Inulin increasing from 6.0 to 7.1 and 7.2 for 2 Hz and 5 Hz, respectively. The absolute reabsorption decreased, however, and indeed not far from the decrement in glomerular filtration.It is concluded that sympathetic nerve activity acts in the direction of fluid conservation, by reducing the glomerular filtration and increasing the fractional reabsorption. The hemodynamic effects will play the dominant role even at 2 Hz stimulation.

Erythrocyte and Albumin Distribution in the Kidney Following Warm Ischemia: A Study in Rats

A dark zone of probably stagnant erythrocytes, localised primarily to the inner stripe of the outer medulla, is always found in acute renal failure caused by clamping of the renal artery for 45 min. To test the possible accumulation of red cells, the regional renal red cell content was investigated with 51Cr labelled red cells injected before, during and 10 min after the recirculation. Analyses were made of the volumes of (1) cells remaining from the period of clamping, (2) cells aggregated 0--10 min after recirculation and (3) cells still circulating 10--20 min after recirculation. In the inner stripe the total red cell volume was 21.8 +/- 2.2 microliter . 100 mg-1 (control value 9.3 +/- 0.6), where 26% remained from the period of clamping, 46% had accumulated 0--10 min after recirculation, and only 28% had entered the region 10--20 min after recirculation. The same pattern of response, though less pronounced, was also found in the inner zone. In the cortex the total red cell volume was 6.3 +/- 1.2 microliter . 100 mg-1 (control value 4.4 +/- 0.3), where 24% remained from the period of clamping, 32% were accumulated and 44% remained circulating. The plasma volume as investigated from 131I-labelled albumin was markedly increased in all zones, probably due to extravasation of the tracer. It is suggested that red cell accumulation plays an important role for the medullary ischemia found in ischemic acute renal failure.

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.

Transvascular fluid exchange in the tracheal mucosa.

Abstract The fluid balance of the rabbit tracheal mucosa was investigated with the micropuncture technique and the microsphere method was used for blood flow measurements. Under resting control conditions the blood flow was 0.62 ± 0.41 ml/min · g of tissue; it increased to 3.22 ± 1.55 ml/min · g when the trachea was divided by a midline incision and fixed with two clamps for the micropuncture experiments. The hydrostatic pressure in the early part of the capillary was 28 mm Hg, in the middle part 17 mm Hg, and in the late part 14 mm Hg. The pressure in the dense network of sinusoidal submucosal veins was 12 mm Hg. The interstitial pressure was 3–4 mm Hg. The plasma colloid osmotic pressure, as estimated from protein data, was 21 mm Hg, and that in the interstitium or terminal lymph was 19 mm Hg; thus they were almost identical. This was due to a heavy leakage of protein resulting from the irritation caused by the incision and clamp-fixation and resembled any case of irritation. With a horizontal body posture there is an outwardly directed filtration in all vascular segments. Part of the fluid will form the fluid layer on the tracheal epithelium and the mucus. The rest is drained, together with the proteins, by the richly developed lymphatic system. In an upright body posture, significant resorption will take place via the submucosal venous plexus, with less risk of edema.

Oxygen radicals in postischaemic damages in the kidney.

SummaryOxygen radicals in postischaemic damages in the kidney: M. Wolgast, A. Bayati, O. Hellberg, Ö. Källskog, K. Nygren and G. Öjteg, Inst. of Physiology and Medical Biophysics, University of Uppsala, Sweden; Ischemic acute renal failure is characterized by a severe depression of the glomerular filtration rate (GFR), isosthenuria and deficient potassium secretion, whereas the total renal blood flow may remain largely intact. As to these symptoms, it would seem established that the depression of GFR results from an ischaemia-induced augmented aging and hence rejection of tubular cells, which thence blocks the tubular lumen. As expected this blockade can be prevented by osmotic diuretics. The isosthenuria and the deficient potassium excretion, on the other hand, results probably from a medullary ischaemia, the latter due to the action by oxygen-derived free radicals in the sense the subsequent damage to the capillary membrane leads to a massive extravasation of plasma and consequent intracapillary trapping of red cells. In line with this idea, superoxide-dismutase (SOD) or Allopurinol may ameliorate these changes. In the recovery phase of postischaemic renal failure, the most prominent feature is the blocking of the ascending loop of Henle with Tamm/Horsfall-protein which, if not washed-out during the first week, leads to a complete degeneration of the nephron. Unfortunately, the process would seem to be unaffected by treatment with e.g. osmotic diuretics and SOD or Allopurinol.