Robert F. Pitts memorial lecture. H+ secretion in renal cortical tubules: kinetic aspects

Intraperitoneal Administration of Recombinant Human Erythropoietin

Objective

To determine the efficacy and safety of intraperitoneal administration of recombinant human erythropoietin (rHuEPO) in continuous ambulatory peritoneal dialysis (CAPD) patients compared to subcutaneous rHuEPO.

Design

Prospective analysis of an open, nonrandomized investigation.

Setting

Outpatient CAPD clinics in two university hospitals.

Patients

Nine adult CAPD patients receiving rHuEPO intraperitoneally and 8 patients receiving rHuEPO sub-cutaneously.

Intervention

One hundred units of rHuEPO per kilogram of body weight were administered three times a week for 8 weeks or until the target hematocrit of 35% was reached. Thereafter, dosages of rHuEPO were adjusted for response. Intraperitoneal rHuEPO was administered in 1 L of dialysis solution during the night.

Measurements

Efficacy was assessed by measuring the increase in hemoglobin. Tolerance was assessed by monitoring side effects.

Results

In the first 8 weeks of treatment hemoglobin concentration increased from 64.5±12.9 glL to 98.3±16.1 g/L (p<0.0005) in the intra peritoneally treated group. In the subcutaneously treated group hemoglobin increased significantlyfaster (p<0.05) from 72.5±4.8 g/L to 119.2±11.3 g/L (p<0.0005) in the same period. Antihypertensive medication had to be increased or instituted in most of the patients in both groups. The incidence of peritonitis in the intraperitoneally treated group was not increased when compared to the pretreatment incidence.

Conclusions

Subcutaneously administered rHuEPO is superior to intraperitoneally administered rHuEPO with regard to the required dosages. However, the results of this study show that intraperitoneal administration of rHuEPO might be a convenient and safe alternative when subcutaneous administration is undesirable.

Proteolytic activity and free amino acid concentrations in polymorphonuclear leucocytes

Polymorphonuclear granulocytes (PMN) are valuable tools for evaluating amino acid (AA) metabolism in nucleated cells, although variations of free amino acid concentrations due to the methods used for the separation of the cells and the procedures used for lysis have been reported. Furthermore, analytical variations in PMN AA concentration may be induced by protease activation during preparation, so that free AA detected in cells could originate from proteolysis other than from the physiological metabolic pathways and transport systems. To study this possibility we measured granulocyte protease activity and AA concentrations in cell suspensions processed with and without the addition of antiproteolytic agents. Granulocyte AA concentrations and protease activity in samples treated with antiproteolytics were 8-15 times lower than in samples processed without antiproteolytics. The use of protease inhibitors throughout the sample preparation is necessary for reliable estimation of free AA in granulocytes.

Effect of medium tonicity on transepithelial H(+)-HCO3-fluxes in rat proximal tubule

1. The effect of luminal and capillary perfusion with hypotonic or hypertonic solutions containing 25 mM NaHCO3 or NaH2PO4 plus NaCl, K+, Ca2+, Mg2+ and acetate at an osmolality of 100 or 500 mosmol kg-1 on rat proximal H+ secretion was estimated by monitoring luminal pH with Sb microelectrodes. The results were compared to perfusions with the same ionic concentration in which tonicity was adjusted to 300 mosmol kg-1 with raffinose. 2. The kinetics of acidification of luminally injected bicarbonate buffer permits evaluations of H(+)-HCO3-fluxes as well as stationary pH gradients; the kinetics of alkalinization of luminally injected acid phosphate buffer indicates H(+)-HCO3-backfluxes from blood to lumen. 3. In alkalinization experiments, luminal perfusion with hypotonic solution during presence of blood in capillaries or hypotonic capillary perfusion leads to a decrease of stationary pH, an increase of alkalinization half-time and consequently a decrease of passive H(+)-HCO3-backflux. 4. In alkalinization experiments, during luminal and/or capillary perfusions with hypertonic solutions, no significant differences in the stationary pH, alkalinization half-time and H(+)-HCO3-backflux were found. 5. During acidification experiments, with both hypo- and hypertonic perfusions, no significant differences in stationary pH, acidification half-time and H(+)-HCO3-flux were observed. 6. Luminal perfusion with hypotonic solution increases specific epithelial resistance in the presence of blood in capillaries. Luminal perfusion with hypertonic solution does not change this parameter. 7. Volume changes, measured by the split-drop method, are slow during the first 30 s and do not explain the increased alkalinization half-time during luminal perfusion with hypotonic solution, since this is the period of fastest pH change. 8. Luminal perfusion with hypotonic solution decreases apparent H+ permeability in the presence of blood or hypotonic solution in capillaries. Hypertonic solutions in all experimental conditions had no significant effect on this parameter. 9. The data indicate that decrease of tonicity of fluids in contact with proximal tubule epithelium affects passive H(+)-HCO3-backflux, which proceeds in part through the shunt path, while acidification (H+ secretion), which is transcellular, is not affected by extracellular tonicity.

Long-term effect of amino-acid dialysis solution in children on continuous ambulatory peritoneal dialysis

The study involved eight metabolically stable children, with chronic renal failure on continuous ambulatory peritoneal dialysis (CAPD) whom we followed for 12-18 months. For the first 6 months CAPD was performed with dextrose; for the subsequent 6-12 months the morning exchange was substituted with a 1% amino-acid (AA) solution. The following parameters did not change during the study: serum creatinine, uric acid, inorganic phosphate, serum bicarbonate, potassium, cholesterol, triglycerides, total protein, albumin and transferrin. The only parameter that changed was blood urea nitrogen, which increased moderately. The anthropometric parameters did not show significant variation before and after AA dialysis. The plasma AA profile, which under basal conditions showed lower levels of several essential AAs, improved during the treatment period, with a partial correction of the imbalance. It is possible that this correction of plasma AAs may positively influence the metabolism of some organs such as the brain, muscle and those of the hepatosplanchnic region. The intracellular pool of free AAs, measured in polymorphonuclear leucocytes, was severely altered before the treatment and after 6 and 12 months showed only minor variations. It is possible that some modifications in the proportion of the different AAs in the dialysis solution or an improvement in the concentration or in the number of exchanges per day are necessary in order to change the nutritional status and to modify the intracellular AA pool.

Effect of amphotericin B on renal tubular acidification in the rat

Amphotericin B, a polyene antibiotic known to induce cation-selective pore formation in biological cell membranes, was given to rats by peritoneal injection (10 mg/kg for 21-26 days) or added to luminal perfusates (2 x 10(-5) M). Kinetics of tubular acidification and alkalinization after perfusion with alkaline or acid phosphate Ringer's solution was studied by means of double barrelled antimony/reference microelectrodes in cortical distal tubules. Stationary pH increased both in early and late distal segments. Acidification and alkalinization half-times decreased markedly from 15-18 s to 6-8 s, a value similar to that found in proximal tubule. Net H-ion secretion rates as well as H-ion back-flux approximately doubled after Amphotericin B. Apparent H-ion permeability of distal tubule epithelium measured during perfusion of lumen and peritubular capillaries with phosphate Ringer's solutions doubled both in early and late segments. These data show that amphotericin B produces a distal acidification defect which impairs formation of normal transepithelial pH gradients by increasing H-ion back-flux without reducing rates of net H-ion secretion.