Site and mechanism of the action of diuretics

The mechanism of action of diuretics can be established by studying the molecular mechanism of action, the site of action within the nephron, and the relationship between the pharmacokinetics of the diuretic and its effect. The molecular mechanism of action is known for diuretic agents such as acetazolamide (carbonic anhydrase), theophylline (phosphodiesterase), digitalis glucosides (Na-K-ATPase), spironolactone (aldosterone antagonism) and dopamine (specific receptors?). The "receptor" for the clinically most important diuretics, i.e. loop diuretics, thiazides, and other potassium-sparing diuretics is, however, unknown. It appears from recent studies of the ion transport in the diluting segment that there probably is a sodium-chloride co-transport in this segment and that loop diuretics specifically inhibit the active chloride transport. The main site of diuretic action is well established for the different groups of diuretics: carbonic anhydrase inhibitors act on the proximal tubulus, loop diuretics on the diluting segment, thiazides on the cortical diluting segment/distal tubulus, and potassium-sparing agents on distal tubulus/collecting ducts. Moreover, some diuretics have additional tubular sites of action. It is also important to realize that other effects of diuretics, e.g. inhibition of the tubuloglomerular feedback mechanism or renal and extra-renal hemodynamic effects, can modify the tubular diuretic effect. Finally, the renal handling of diuretics is of importance to the diuretic effect by determining the concentration of the drug at the "receptor" sit (s). It is emphasized that knowledge of the different aspects of the mechanisms of action of diuretics is a prerequisite for rational use of diuretics, clinically as well as experimentally.

Influence of food intake on electrocardiograms of healthy male volunteers

OBJECTIVE

To study the influence of food intake on electrocardiogram (ECG) variables (heart rate, QT-, QTc-, PR-intervals, QRS-time) and morphological alterations of the T-waves in 12 healthy male volunteers.

METHODS

The study was of open, three-period crossover design. On each occasion, all subjects fasted from midnight. During two of the study periods, the subjects were given a standardised meal at 1.5 h and 5.5 h after the baseline assessments, respectively, whereas, during the third period, they remained fasting for the entire study period of about 9 h. ECG and blood pressure were recorded at baseline and thereafter every hour for 8 h.

RESULTS

No ECG changes were observed following the fasting condition, whereas a clear change in ECG and an increased heart rate were recorded in response to the meal intake during the other two periods. The most prominent ECG effect was the change in the size and shape of the T-waves, which were described as flattened to biphasic and, occasionally, negative. These alterations were most pronounced in the precordial leads V4 to V6 in the ECG recording immediately following the meal intake, with a gradual return to baseline conditions over 4-5 h. Moreover, a transient increase of supine systolic blood pressure was also recorded in response to the meal intake.

CONCLUSIONS

The intake of a meal can cause clear and consistent ECG changes in healthy male subjects, comprising increases in heart rate as well as alterations in the size and shape of the T-waves (flattened to biphasic and, occasionally, negative). Also, a post-meal increase in the supine systolic blood pressure was recorded.

Conjunctival oxygen tension is influenced by plasma and blood volume, and flow through the external carotid artery

An investigation of the feasibility and validity of measurement of the conjunctival oxygen tension as a monitor of peripheral circulation, blood and extracellular fluid volume and cerebral circulation was carried out in 7 healthy volunteers and 5 unconscious critical care patients with proven total cerebral infarction. The healthy volunteers were subjected to changes in hydration achieved by the administration of furosemide and subsequent rehydration by administration of normal saline. Conjunctival oxygen tension was found to be a sensitive indicator of changes in the degree of hydration presumably by its ability to detect changes in peripheral circulation depending upon circulating blood and extracellular fluid volume. A drawback is that other stimuli of the sympatho-adrenergic system such as temperature and pain, interfere with measurement in the conscious volunteer. In patients with presumed total brain infarction the conjunctival PO2 cannot be used as a reliable monitor of cerebral blood flow because of varying perfusion of the palpebral conjunctiva from the external carotid artery in the occasional patient.

Tolerability of remoxipride in the long term treatment of schizophrenia. An overview

506 patients with schizophrenia, diagnosed according to Diagnostic and Statistical Manual of Mental Disorders (DSM-III) criteria, were included in a long term treatment programme with remoxipride, a selective dopamine (D2)-receptor antagonist. This overview includes pooled data from all patients who have been treated long term with remoxipride in clinical trials, focusing on patients treated for more than 6 months (n = 283). Remoxipride was administered in daily doses of 75 to 600mg. The assessment tools were Brief Psychiatric Rating Scale (BPRS), Clinical Global Impression (CGI), Simpson and Angus scale, Abnormal Involuntary Movements Scale (AIMS) for abnormal involuntary movements, adverse events/symptoms using a 26-item checklist, clinical chemistry, and haematology and cardiovascular investigations. The majority of patients had a long duration of illness (median 11 years). 67% of patients (340/506) withdrew from treatment before 12 months and 44% (223/506) stopped treatment before 6 months. The median BPRS total score decreased during the first 3 months from 23 to 12, and this level of improvement was maintained throughout the 12-month period. Treatment-emergent adverse events reported by more than 5% of the patients were insomnia, tiredness, drowsiness and tremor in the group treated for 6 to 12 months. No symptoms, including checklist extrapyramidal symptoms (EPS), were reported by more than 5% of patients treated for 12 months. Low frequencies of EPS according to the Simpson and Angus scale were seen in patients treated for more than 6 months (n = 147). A small but statistically significant reduction of the mean total AIMS score from baseline to last rating was observed. There were infrequent changes in heart rate, resting diastolic blood pressure and electrocardiogram (ECG). Clinical chemistry and haematology data showed no evidence of clinically significant changes over time during the 12 months of treatment. Among 506 patients, 7 suicides and 7 suicide attempts occurred during the study period. Other serious adverse events were abnormal liver function test (2 cases), gastrointestinal, urinary retention, status epilepticus (psychotic polydipsia), granulocytopenia (1 each) and myocardial infarction (5 cases). Remoxipride is of potential value as a drug which is both effective and well tolerated in the long term management of patients with schizophrenia.

Improvement of renal preservation by adding lidoflazine to University of Wisconsin solution. An experimental study in the rat

The purpose of this study was to investigate the possibility of improving the organ preservation properties of the University of Wisconsin (UW) solution by adding the calcium entry blocker lidoflazine. We also investigated the possibility of decreasing the cold ischemia and reperfusion damage by pretreatment with lidoflazine of the donor and/or recipient. The protective effects of lidoflazine treatment were estimated by measuring the amount of trapped erythrocytes in the rat renal medulla after 48 h of cold storage, subsequent transplantation, and 20 min of reperfusion. Lidoflazine (20 mg/liter) added to the UW solution decreased the amount of erythrocyte trapping from 14.8 +/- 3.1% in controls to 8.6 +/- 1.7% (P less than 0.01). The flow rate of the flush-out solution during the harvesting procedure was also significantly (P less than 0.01) increased when lidoflazine was included in the UW solution (1.10 +/- 0.21 ml/min vs 0.75 +/- 0.22 ml/min). Administration of lidoflazine (0.28 mg/kg body wt) to the donor and/or the recipient did not further reduce the postischemia/reperfusion damage as estimated by the degree of erythrocyte trapping. In conclusion, the results indicate that the preservation properties of the UW solution can be significantly improved by adding lidoflazine to the solution.

Pharmacokinetics of recombinant human superoxide dismutase in healthy volunteers

We studied the pharmacokinetics and effects of recombinant human superoxide dismutase (rhSOD) in 32 normal human volunteers after intravenous bolus doses from 1 mg/kg to 45 mg/kg in a single-blind, placebo-controlled, crossover design. The drug was well tolerated. Neither cardiovascular nor renal function, such as the echocardiographically determined cardiac index, insulin or para-aminohippurate clearance, or the urinary excretion of beta 2-microglobulin or N-acetylglucosaminidase, was affected. Pharmacokinetic analysis by use of noncompartmental methods showed an overall half-life of rhSOD to be about 4 hours for doses from 3 mg/kg to 45 mg/kg. The peak concentrations ranged from 24 to 837 mg/L, and urinary excretion increased from 3% to 57% of total dose after single intravenous bolus administrations of the drug from 1 mg/kg to 45 mg/kg. The mean renal clearance of rhSOD initially increased with dose then plateaued at the highest dose, whereas the nonrenal clearance decreased with dose to a plateau; total clearance remained essentially constant. The progressive increase in renal clearance may be explained by saturation of the tubular reabsorption and degradation of the protein, a mechanism previously described in animal models.

Enhanced local production of complement components in the small intestines of patients with Crohn's disease

There is evidence that complement components may be formed locally in inflammatory lesions containing monocytes and macrophages. To investigate the role of complement in Crohn's disease we measured jejunal-fluid concentrations of the complement components C4, C3, and factor B by perfusion of a closed segment of the jejunum in 22 patients with Crohn's disease thought to be limited to the terminal ileum. The mean (+/- SEM) jejunal-fluid C4 concentration was 2.0 +/- 0.3 mg per liter, significantly higher than the mean level in 35 healthy controls (0.7 +/- 0.1 mg per liter; P less than 0.001). The mean C3 concentration was 1.0 +/- 0.1 mg per liter in the patients and 0.7 +/- 0.1 mg per liter in the controls (P less than 0.05). The factor B levels were similar in the two groups. Calculated rates of intestinal secretion of these components showed differences of the same magnitude. Leakage of protein from plasma was not increased. The jejunal-fluid:serum ratios of these complement proteins indicated that their appearance in the lumen of the jejunum was due to at least in part to local mucosal synthesis. The increased jejunal secretion of C4, but not C3 or factor B, paralleled the clinical activity of Crohn's disease. Values were normal in first-degree relatives of the patients (n = 13), patients with celiac disease (n = 8), and patients with ulcerative colitis (n = 4). We conclude that increased secretion of complement by clinically unaffected jejunal tissue in patients with Crohn's disease reflects the systemic nature of this disorder and may be due to the stimulated synthesis of complement by activated intestinal monocytes and macrophages.

The jejunal secretion of histamine is increased in active Crohn's disease

Previous studies of mast-cell density and histamine content in biopsy specimens in patients with Crohn's disease have yielded conflicting results. In this in vivo study we have measured the jejunal secretion rate of histamine in patients with Crohn's disease (n = 15) of the terminal small bowel and in healthy controls (n = 24). The secretion studies were performed using a recently developed segmental jejunal perfusion system with a two-balloon, six-channel small tube. The histamine secretion rate was 152 +/- 29 (SEM) ng/cm small intestine per h in patients with Crohn's disease, which meant a significant increase (p less than 0.01) compared with the secretion rate in controls (71 +/- 11 ng/cm per h). Moreover, the secretion of histamine was related to the disease activity. Patients with active disease (n = 8) (i.e., Crohn's disease activity index greater than 150) had a mean histamine secretion rate of 193 +/- 47 ng/cm per h, while patients with inactive disease (Crohn's disease activity index less than 150) had a secretion rate not significantly increased compared with controls (105 +/- 24 ng/cm per h). The present data indicate increased mast-cell involvement of the small intestine in active Crohn's disease of the distal ileum. This finding might reflect the systemic nature of the disease process.

Signs of increased leakage over the jejunal mucosa during gliadin challenge of patients with coeliac disease

Intestinal secretion rates of albumin, hyaluronan, and beta 2-microglobulin (beta 2-micro) were determined under basal conditions and after gliadin challenge of coeliac patients and healthy controls by the use of a jejunal perfusion technique. A new tube system was used where a jejunal segment is isolated between balloons and then perfused with a balanced salt solution. Under basal conditions the secretion rate of albumin was similar in the patients and controls while the secretion rate of the glycosaminoglycan hyaluronan, a high molecular weight connective tissue component, was increased more than two times in coeliac patients. Beta 2-micro was secreted in on average three-fold rates in coeliacs compared with controls. All three substances were secreted at a higher rate in patients with active disease than in those with inactive disease defined by morphological damage in small bowel biopsies. The concentrations in jejunal perfusion fluids relative to serum levels in the coeliac patients were for albumin 0.0007, beta 2-micro 0.10, and for hyaluronan 1.94. Challenge with a single dose of gliadin into the jejunal segment gave within 60 min a significant, about two-fold, increase of the secretion rates of all three measured substances. The appearance of hyaluronan could reflect a gliadin induced mucosal oedema with an enhanced leakage from the interstitial/lymph fluid, rich in this glycosaminoglycan. The observed parallel increases in the jejunal secretion of albumin and beta 2-micro after gliadin challenge are best explained by a similar mechanism.

Challenge with gliadin induces eosinophil and mast cell activation in the jejunum of patients with celiac disease

PURPOSE

The aim of this study was to clarify the role of eosinophils and mast cells in the small bowel in celiac disease.

PATIENTS AND METHODS

Patients with celiac disease (n = 10) were investigated by perfusion of a closed jejunal segment. The concentrations of certain granule constituents from eosinophils, eosinophil cationic protein (ECP), and from mast cells/basophils, histamine, were measured and the jejunal secretion rates of these cellular markers were calculated.

RESULTS

Compared with findings in healthy control subjects (n = 14), increased secretion rates were observed under basal conditions in patients with histopathologically active celiac disease. Gliadin, administered by perfusion to the jejunal segment, induced a fourfold increase in ECP secretion and a twofold increase of histamine secretion in patients with celiac disease (n = 7), but did not influence the secretion rates of these substances in healthy controls (n = 3). The secretion rate of ECP started to increase 20 minutes after challenge of the perfused segment with gliadin and reached maximum levels 40 minutes later. The secretion rate of histamine started to increase 40 minutes after gliadin administration. Concurrently with these inflammatory events, the secretion of albumin was doubled as a sign of increased mucosal leakage.

CONCLUSION

These data indicate that eosinophils and mast cells are both involved in the early gliadin-induced reactions of the small intestine, and suggest that these cells are effector cells participating in the celiac lesion of the mucosa.

Tissue distribution of 125I-labelled carbonic anhydrase isozymes I, II and III in the rat

Carbonic anhydrase (CA) isozymes CA I and CA II were isolated from rat erythrocytes, and CA III from rat skeletal muscle. They were purified to homogeneity and labelled with 125I using the Bolton-Hunter method. The tissue distribution of these [125I]CA isozymes was studied in rats with whole-body autoradiography at various times after an intravenous injection. The distribution pattern showed a remarkable organ specificity. CA I and CA III were to a great extent localized to the renal cortex. This is compatible with renal uptake, secondary to glomerular filtration, of these isozymes. This would be expected from the renal handling of proteins with the following characteristics: molecular weight of 29,000; iso-electric points, pI, around 7.2 and 6.5 respectively. However, CA II of similar molecular shape and size, with a pI of 6.8, remained in the blood and was preferentially localized to the liver. Further studies are needed to clarify why such similar proteins are targeted to different organs.

A new technique for segmental jejunal perfusion in man

A multichannel tube with two occluding balloons was developed for measurements of the secretion of different endogenous substances into a defined segment of the small intestine. The tube was inserted under fluoroscopic guidance with the aid of a guide wire and was in position in the proximal jejunum after 45-90 min. The overall success rate of the complete procedure was 90%. The system prevented contamination of the perfusate from gastric and pancreatic secretion. Major dilution of the intestinal secretion was avoided due to high recovery of the perfusion fluid. The jejunal secretion rates of high and low molecular weight substances, i.e., albumin, beta 2-microglobulin, hyaluronan, and histamine, were tested. The recovery of the effluent fluid and the volume marker 14C-PEG 4000 exceeded 95% and was also stable over the perfusion period. The mean secretion rates in 23 healthy controls of albumin (635 micrograms/cm/h), beta 2-microglobulin (0.87 microgram/cm/h), hyaluronan (1061 ng/cm/h), and histamine (70 ng/cm/h) were also stable during the perfusion period. Ten healthy controls were studied under steady state conditions for 3 h. The concentrations in jejunal perfusion fluid relative to serum levels were for albumin 0.06%, indicating the degree of passive leakage from the plasma compartment to the intestinal lumen. The appearance of the low-molecular weight protein beta 2-microglobulin in perfusion fluid was on average 3% of its circulating levels, suggesting that the concentrative transport from plasma is dependent on the molecular size. The jejunal fluid concentrations of histamine and hyaluronan exceeded their respective concentrations in plasma, indicating that local intestinal secretion/synthesis is mainly responsible for their appearance in jejunal fluid. In summary, the technique is simple, rapid, atraumatic, safe, and reproducible and, potentially, can accurately reflect biochemical processes in the small intestine.

The effect of type of preservation solution and hemodilution of the recipient on postischemic erythrocyte trapping in kidney grafts. An experimental study in the rat

The role of recipient hemodilution for postischemic renal medullary red cell trapping was investigated after different periods of cold storage in a conventional cold storage solution (Sacks'). At all cold storage times investigated (4, 12, 24, and 48 hr) medullary red cell trapping was reduced by isovolemic hemodilution, with about 50% reduction of recipient hematocrit. Trapping was also reduced when a modification of a new preservation solution (University of Wisconsin solution [UW]) was used and compared with flush-out and storage in a standard preservation solution (Sacks'). The combination of hemodilution and preservation in modified UW solution had additional capacity to reduce medullary red cell trapping. Thus, even after 48 hr of cold storage, only a moderate trapping was observed. The results also indicate that measurements of medullary red cell trapping offers an accurate method of grading postischemic renal damage.

Organ flush out solutions and cold storage preservation solutions: effect on organ cooling and post ischemic erythrocyte trapping in kidney grafts. An experimental study in the rat

Three flush out and cold storage solutions were tested for flow rate during flush out, ability to decrease organ temperature, degree of tissue edema and degree of preservation damage of the kidney as measured by the amount of post transplantation erythrocyte trapping in the renal medulla. The solutions tested were a modification of a new perfusion solution (University of Wisconsin; mUW), a standard preservation solution (Sacks') and an extracellular histidine solution (Frödin-Wolgast; FW). The flow rate was significantly higher for FW compared to mUW and Sacks' and consequently a more rapid decrease of organ temperature was achieved. The results also show that edema formation as well as the amount of erythrocyte trapping was lower in kidneys stored in mUW, indicating that mUW is better cold storage solution than Sacks' or FW.

Plasma elimination kinetics and renal handling of copper/zinc superoxide dismutase in the rat

The renal handling of bovine and human superoxide dismutase (SOD) was investigated in Sprague-Dawley and Munich-Wistar rats. Under normal physiological conditions the half-time of the major rapid component of the plasma elimination curve was estimated at 6.0 +/- 0.5 min, the volume of distribution at 35.7 +/- 3.3 ml kg-1, i.e. the plasma volume and the corresponding plasma clearance at 4 ml min-1 kg-1. After a single intravenous dose, most of the enzyme was distributed to and eliminated by the two kidneys, whereas the non-renal clearance was low, 0.5 ml min-1 kg-1. The single nephron filtration of SOD, as assessed from micropuncture of Bowman's space, was 10.4 +/- 1.0 nl min-1, which was 26 +/- 2% of that for inulin. The total elimination of SOD by glomerular filtration would thereby be 2.5 ml min-1 kg-1, i.e. the glomerular ultrafiltration process would account for the largest part of the elimination of SOD from circulating plasma. After the dosage of 20 mg kg-1, about two-thirds of the injected SOD was excreted as the intact molecule into the urine, whereas one-third was found to be reabsorbed and metabolized by the proximal tubular epithelial cells. In animals suffering from unilateral post-ischaemic acute renal failure, the elimination half-time was 13 +/- 1.9 min, a value which increased by 55 +/- 5 min after bilateral functional nephrectomy. By contrast, the distribution volume remained essentially unchanged.

Effects of cold ischemia and reperfusion on trapping of erythrocytes in the rat kidney

After reperfusion of kidneys subjected to a period of warm ischemia, the medulla displays a vascular congestion of erythrocytes, especially in the inner stripe of the outer zone, a phenomenon referred to as "trapping." This trapping causes reflow alterations, thus contributing to postperfusion medullary ischemia. The purpose of the present investigation was to study whether trapping also occurs after reperfusion of kidneys following varying periods of cold ischemia and to determine if there is any correlation between the degree of cold ischemic injury and the extent of erythrocyte trapping. Rat kidneys stored at +4 degrees C for 0-30 h were transplanted into recipient animals pretreated with a 51Cr-labelled erythrocyte suspension. Twenty minutes after reperfusion, the grafts were removed and microdissected into cortex, outer and inner stripes of the outer medullary zone, and inner zone, respectively. The radioactivity of these specimens was measured, and the erythrocyte content for each specimen was calculated. The results show a maximal trapping for cold ischemia time (CIT) of about 12-15 h. A linear correlation between the amount of trapping and CIT could be found in all parts of the kidney (except for the cortex) for CIT 0-15 h. The best correlation was found in the part where the trapping was most prominent, i.e., in the inner stripe. After CIT of 15 h or more, no correlation could be found. It is suggested, as described in models of warm ischemia, that the obstructions of the capillaries by trapped erythrocytes following reperfusion is of pathophysiological significance for the development of post-transplant acute renal failure.(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue distribution of 125I-labelled bovine superoxide dismutase (SOD) in the rat

Bovine copper/zinc superoxide dismutase (SOD) was labelled with 125I using the chloramine-T method. The tissue distribution of 125I-SOD (dose of SOD 5 mg/kg) was studied with whole-body and microautoradiography at various times after an intravenous injection. The distribution of 125I-SOD showed a remarkable organ specificity in that the localization of the enzyme to the kidneys and the urinary tract completely dominated the autoradiograms. The time pattern of localization of 125I-SOD also gives a clear picture of the renal handling of the enzyme in that, as a consequence of the renal elimination, the enzyme rapidly disappears from the circulation with an elimination half time of about 6 min. Up to 20 min. after the injection, there were high concentrations of 125I-SOD in the renal pelvis, ureter and urinary bladder showing that in addition to renal uptake there was an initial substantial urinary excretion of the enzyme. From the microautoradiography it is clear that the grains were exclusively localized over proximal tubular cells and tended to be concentrated at the luminal rather than the peritubular side of tubule. This would be compatible with renal uptake secondary to glomerular filtration of 125I-SOD, which is what one would expect from the renal handling of a protein with a molecular weight around 31,000 and an isoelectric point around pH 5.4. Pretreatment with a large dose of SOD (88 mg/kg) tended to competitively decrease the renal uptake of labelled SOD after 5 min. and apparently further increase its renal excretion. However, a noticeable renal uptake of 125I-SOD was still apparent.(ABSTRACT TRUNCATED AT 250 WORDS)

Preferential localization of 3H-pentosanpolysulphate to the urinary tract in rats

Endogenous glycosaminoglycans probably have a protective effect in the urinary tract, e.g. against stone formation. The synthetic sulphated polysaccharide pentosanpolysulphate (PPS) has been suggested to exert a similar protective effect e.g. by inhibition of crystallization and bacterial anti-adhesion. We have studied the distribution in rats of tritium-labelled PPS. Chromatography showed this material to contain two distinct peaks with approximate molecular weight around 2.700 (60-70%) and 1.000 (30-40%) daltons. PPS was administered orally and intravenously (5 mg/kg b.wt.) to Sprague-Dawley rats, which were killed 1 and 4 hours later, respectively, and subjected to whole-body autoradiography. Autoradiograms of sections from intravenously injected rats showed an extensive distribution of radioactivity in the whole animal, with a notable labelling of connective tissues, while bone and cartilage had low activity. There was upper intestine activity, suggesting some hepatic excretion. The most conspicuous finding, however, was the high concentration in urine and a preferential localization of activity corresponding to the lining of the urinary tract (pelvis, ureter, and bladder). The distribution was similar, but the activity lower after oral administration. In one experiment, PPS was applied intravesically under anaesthesia, with and without epithelial destruction caused by instillation of 0.4 M HCl. After vigorous rinsing, with saline, the radioactivity was still retained in the bladder wall. In other intravenous experiments, the bladder was extirpated, everted and rinsed in saline or urea of increased osmolality. High amount of radioactivity could be rinsed off by 0.5 M saline. Chromatography of the rinsing solution showed presence of both fractions of PPS previously found in the injection solution.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of ischaemic acute renal failure with superoxide dismutase and sucrose

The preventive effects of intravenously administered superoxide dismutase (SOD) and of SOD combined with sucrose on acute renal failure were investigated in rat kidneys exposed to 45 min of warm ischaemia. Superoxide dismutase (20 mg) given just before primary ischaemia and in the early recirculation phase was found to ameliorate the red cell aggregation in the renal medulla, in particular, in the inner stripe of the outer zone the volume of trapped red cells decreased from 11.2 +/- 1.6% in untreated animals to 0.02 +/- 0.001%, thus allowing improved restoration of medullary blood flow. This was also accompanied by an expected restoration of the urine osmolality reaching almost 400 mOsm kg-1 after administration of SOD + sucrose. Superoxide dismutase also restored the capillary macromolecular permeability as evidenced by normalization of plasma to lymph transport of proteins. Micropuncture studies showed that in ischaemically damaged but untreated kidneys the tubules were obstructed and that the proximal tubular pressure rose to such a level that the net driving force for filtration approached zero. This explains the marked decrease in glomerular filtration rate (GFR) from a normal value of about 1 ml min-1 to 0.01 +/- 0.02 ml min-1. After treatment with SOD the tubules were still largely obstructed, resulting in a depression of the net driving force and a decrease in single nephron glomerular filtration rate (SNGFR) to about 11 nl min-1, that is, to only 25% of the normal SNGFR. The total filtration was 0.09 +/- 0.04 ml min-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetic-pharmacodynamic relationship of piretanide in healthy and uremic subjects. Determinants of the diuretic effect of a loop diuretic

The pharmacokinetics of the loop diuretic piretanide and its diuretic effects were studied in 6 healthy volunteers, 12 pre-dialysis (GFR 7-28 ml/min) and 10 dialysis patients (c-creat. 1-7 ml/min). Single doses up to 96 mg i.v. and orally were well tolerated and audiometry showed no hearing changes. Pharmacokinetic data showed rapid and almost complete absorption (bioavailability 92%) and a rapid elimination with renal clearance of 50% of the total 200 ml/min in the normals and renal clearance of about 50% of actual GFR in the patients. Extrarenal clearance was the same in normals and patients. The rapid extrarenal elimination reduces the risk of accumulation in renal patients but also reduces the active fraction of the dosage being cleared by the kidneys. Therefore, a high dosage and high plasma levels of piretanide were necessary for diuretic effect in uremic patients. The relation between the urinary piretanide excretion rate and the chloruretic effect was similar in normals and uremic patients; Cl- excretion increased 40 mMol per mg piretanide excreted.

Some effects of metolazone on electrolyte transport

Metolazone action was studied 1) in vitro on isolated operculum of Fundulus heteroclitus (active chloride transport) using an Ussing chamber (metolazone conc 500 microM) and in vivo 2) using the modified Sperber technique in the hen (metolazone infusion rate 0.75-1.2 micrograms/kg/min) and 3) in healthy volunteers using clearance techniques (metolazone infusion rate 10 mg/h). Metolazone reduced (p less than 0.05) short circuit current potential differences with 20% from average control values (p less than 0.05), while direct current resistance was unchanged. This is comparable to thiazide but much lower than loop diuretic effects. True tubular excretion fraction of metolazone before and after novobiocin (2.7 mumol/kg/min coinfusion averaged 14.1 and 4.5%, resp. (p less than 0.01; n = 8). Thus metolazone is partly eliminated by renal tubular secretion. However, the diuretic effect (sodium, chloride and potassium excretion)--and clearances of Cr51-EDTA and I125-Na-o-iodohippurate--were symmetrical, i.e. independent of metolazone urinary excretion rate, as previously shown for thiazides. Renal clearance of metolazone in healthy volunteers. (HPLC-method) averaged 173 +/- 20 ml/min (n = 8). Probenecid (1 g iv.) significantly reduced the renal clearance of metolazone to 33 +/- 7 ml/min and potassium excretion with maximum 30%, while diuretic and saluretic effects were significantly increased with maximum 30%. Thus, also in humans the diuretic effect of metolazone is not coupled to the urinary excretion rate of the drug, but suggests that its diuretic effect is elicited primarily from the peritubular side of the nephron. Probenecid apparently dissociates sodium from potassium excretion effects of metolazone. This implies a luminal, sodium-independent kaliuretic effect of the drug.

Renal handling and effects of [3H]digoxin and interactions with quinidine in the avian kidney

Renal handling and effects of tritium digoxin and interactions with quinidine in the avian kidney were studied using a modified Sperber technique. Results showed that tritium digoxin was extracted at the peritubular side of the nephron in a process competitively inhibited by increasing amounts of unlabelled digoxin. Light microscope autoradiography showed distinct concentrations of silver grains only over distal tubules in the injected kidney. Inhibition of the proximal tubular transport systems for organic anions and cations, respectively, did not change extraction. Addition of quinidine to the injection solution up to an estimated concentration of 1.4 X 10(-5) M in systemic blood significantly lowered 1 min peritubular extraction of tritium digoxin. However, when the amount of quinidine was further increased, extraction of tritium digoxin augmented significantly. Tritium recovery in urine after renal portal bolus injection of tritiated and unlabelled digoxin already showed a distinct ipsilateral peak 2 min after injection with an equally distinct peak of ipsilateral sodium excretion appearing 1 min later. When quinidine was added to the bolus ipsilateral tritium recovery in urine (0-7 min) was halved, with the true tubular excretion fraction (TTEF) lowered by two-thirds, but without changes in the magnitude of ipsilateral natriuresis. Contralateral natriuresis increased more than four-fold with quinidine in the bolus in spite of unchanged tritium recovery in the urine. Thus, our results show tritium digoxin to be extracted from peritubular blood through a specific process probably localized to the distal nephron of the avian kidney.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum azathioprine and 6-mercaptopurine levels and immunosuppressive activity after azathioprine in uremic patients

The pharmacokinetics of azathioprine (AZA) and 6-mercaptopurine (6-MP) was studied in uremic patients after 100 mg AZA intravenously (fifteen patients) and orally (eight patients). 6-MP was analysed with gas chromatography mass spectrometry following extractive alkylation. AZA was determined indirectly assuming quantitative conversion to 6-MP in whole blood. The plasma concentration of AZA fell rapidly after i.v. administration. The mean half-time of elimination for the first rapid phase (t1/2 alpha) was 6.1 min (S.D. +/- 4.1) and for the terminal phase (t1/2 beta) 50 min (+/- 31). The total plasma clearance (Cl) was 6.9 1./min (+/- 3.0). AZA was rapidly converted to 6-MP in vivo, and maximal plasma concentrations of 6-MP were found as early as 5 min after i.v. injection of AZA. The mean t1/2 alpha was 4.6 min (+/- 2.2), t1/2 beta 74 min (+/- 58) and Cl 8.0 1./min (+/- 5.8). The plasma levels of both AZA and 6-MP were either low or undetectable 4-6 h after dose. In erythrocytes AZA levels were low or undetectable indicating rapid conversion to 6-MP in these cells. 6-MP concentration - time curve in erythrocytes was similar to that in plasma, except for a somewhat slower terminal phase of elimination. Oral administration of AZA generated flat plasma curves for AZA and 6-MP. The area under the concentration - time curve (AUC) was considerably smaller than after i.v. administration, 18 and 41% for AZA and 6-MP, respectively. There seems to be little danger of accumulation of AZA/6-MP in uremia. We also studied inhibition of Leucoagglutin (LA) stimulated lymphocyte proliferation by patient plasma at different times in six of the patients following AZA i.v. Sera drawn at 5, 10 and 30 min significantly inhibited the LA-induced proliferation, with an estimated minimum effective concentration of 6-MP in the cultures of about 0.02-0.04 microM. This suggests the possibility of a therapeutic effect even of the low plasma levels of 6-MP obtained after AZA orally. The combined use of sensitive pharmacokinetic and immunological assays as described should be useful in studying the relationship between plasma levels of AZA/6-MP and their immunosuppressive effect and toxicity.

Renal handling of 125I-labelled insulin in the hen

Renal handling of 125I-insulin was studied using a modification of the Sperber technique. Results showed 125I-insulin to be extracted at the peritubular side of the nephron in a process that was competitively inhibited by increasing amounts of unlabelled insulin, but not ACTH, in the injection mixture. When unlabelled insulin instead was injected 30 sec after the labelled insulin it showed significantly less interference with peritubular extraction of 125I-insulin, indicating strong attachment to the cell membrane or possible internalization of 125I-insulin into proximal tubular cells. Light microscope autoradiography 1 min after injection of 125I-insulin showed grains over proximal tubules only. On the ligated side localization was preferably peritubular while on the control side it was luminal. Electron microscope autoradiography showed sparsely distributed grains, however, frequently located over basal parts of proximal tubular cells. Pretreatment with lysine hydrochloride lowered renal extraction of 125I-insulin and increased urinary recovery of iodine label bilaterally. 125I-glucagon and 125I-C-peptide were not extracted from the peritubular circulation. In conclusion, the model has provided evidence of a rapid and significant peritubular extraction of 125I-insulin by proximal tubular cells in a process probably involving specific insulin receptors. Following receptor binding probably only minor amounts of 125I-insulin enters the proximal tubular cells, while the greater part is degraded at the cell surface or released into the circulation.

Acute tolerance to furosemide diuresis in humans. Pharmacokinetic-pharmacodynamic modeling

Furosemide, 40 mg, was given to eight healthy volunteers as an i.v. dose and as oral doses (tablet and solution) with and without food intake. The urine and plasma were sampled frequently and analyzed on their content of furosemide (high-performance liquid chromatography). The urine flow and chloride excretion rate were used as measures of the effect. In spite of a 3-fold difference (28 vs. 9 mg/8 hr, P less than .001) in the cumulative urinary excretion of furosemide between i.v. and postprandial oral administration, no significant difference in the diuretic effect was found (2-2.2 liters/8 hr). The drug excretion-response curves showed parallel shifts depending on mode of administration of furosemide. Clockwise hysteresis, indicating acute tolerance development to the diuretic effect, was seen after the oral doses after food intake. This within-dose development of tolerance was modeled with an extended Hill equation. The tolerance development seems to have a near relationship to acute volume depletion (inadequate substitution of urine losses), probably activating some intrarenal mechanism for extracellular fluid volume preservation. Thus, the time course of furosemide excretion, as well as the degree of renal compensation, determine the renal sensitivity to furosemide. This has important implications for the proper design and interpretation of studies of the excretion-response relationship of diuretics.

Renal tubular accumulation of organic substances: a new in vivo method which differentiates between luminal and peritubular uptake

Using a modification of the Sperber technique we studied cellular uptake of organic substances in the kidney. A test substance was mixed with an extracellular marker (ethylenediaminetetraacetate or inulin), both radiolabelled with an activity ratio close to I, and injected into the renal portal system on one side via a leg vein. The animals were killed 1-10 min after injection and the radioactivity in different organs determined. Results showed significantly higher ipsilateral (injection) to contralateral (control) kidney ratios (substance to marker) at 1 min after injection for 125I-Na-o-iodohippurate (125I-Hipp; P less than 0.001), 14C-tetraethylammonium bromide (14C-TEA; P less than 0.001), 3H-dihydromorphine (3H-DHM; P less than 0.01), and 125I-iothalamate (P less than 0.01), with a progressive decrease in injection kidney ratios for 125I-Hipp and 14C-TEA when death occurred after a longer period. Inhibition of renal tubular transport with novobiocin or mepiperphenidol markedly reduced 1- and 4-min injection kidney ratios for 125I-Hipp and 14C-TEA, respectively. When death occurred after a longer period, ratios in both kidneys increased significantly for 125I-iothalamate. A good correlation was found between peak cellular accumulation in the kidney and excretion efficiency of test substances. Thus, the results indicate that 125I-Hipp, 125I-iothalamate, 14C-TEA, and 3H-DHM were accumulated from the peritubular side of the nephron through the transport systems for organic acids and bases, respectively, and that 125I-iothalamate also showed luminal uptake. In conclusion, this new in vivo technique is simple and well suited for studying renal tubular accumulation of organic substances and offers the advantage of being able to distinguish luminal from peritubular uptake.

Is 125I iothalamate an ideal marker for glomerular filtration?

The triiodinated angiographic contrast medium, iothalamate, has (usually labelled 125I) been used extensively as a marker for glomerular filtration. We have studied the renal handling of 125I iothalamate (IOT) in vivo and in vitro in several species. In renal cortical slices from chicken, rabbit, rat, and monkey, the tissue-to-medium ratio of IOT was twice that of 51Cr-EDTA (EDTA) at 37 degrees C; a difference that was abolished at 0 degree C and markedly reduced by added o-iodohippurate or iodipamide. In five chickens the steady-state renal clearance of IOT (CIOT) was twice (P less than 0.05) that of EDTA (CEDTA) or 3H inulin (C1); a difference that was abolished by administration of 100 mg/kg/hr of novobiocin, an organic anion transport inhibitor. CEDTA was similar to C1 before as well as after transport inhibition. Utilizing the Sperber technique the mean apparent tubular excretion fraction (ATEF) of IOT was 8%, while that of EDTA was 1% (P less than 0.01; N = 10). After novobiocin coinfusion (new steady-state) ATEFIOT was significantly reduced (P less than 0.01) and not different from that of EDTA (-1%). In the same animals the total urinary recovery of IOT was 84 and 57% (P less than 0.01) before and after novobiocin, respectively, while corresponding values for EDTA was unchanged by the inhibitor. In seven rats the renal extraction of IOT was reduced from 29 to 17% (P less than 0.05) by coinfusion of probenecid (5 mg/kg/hr). Corresponding extractions were 82 to 34% (P less than 0.005) and 22% (unchanged) for PAH and EDTA, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of furosemide in man after intravenous and oral administration. Application of moment analysis

Furosemide 40 mg was administered to 8 healthy subjects as an i.v. bolus dose, as 1 tablet in the fasting state, and as 1 tablet and a solution after food intake. The i.v. data gave a total body clearance of 162 +/- 10.8 ml/min and a renal clearance of 117 +/- 11.3 ml/min; the volume of distribution at steady state was 8.3 +/- 0.61. Oral administration gave a bio-availability of the tablet (fasting) of 51%. Food intake slightly reduced the bioavailability, but not to a significant extent. There was no significant difference in availability between the tablet and the solution. Moment analysis gave a mean residence time after the i.v. dose, MRTi .v., of 51 +/- 1.5 min. The mean absorption times (MAT) for all oral doses were significantly longer than the MRTi .v., indicating absorption rate-limited kinetics of furosemide. On average, food delayed the absorption by 60 min. The MAT for the tablet in the postprandial state was significantly longer than for the solution, indicating dissolution rate-limited absorption of the tablet.

Steady state pharmacokinetics of trimethoprim 300 mg once daily in healthy volunteers assessed by two independent methods

The steady state pharmacokinetics of trimethoprim was determined after 300 mg orally once daily to 6 healthy volunteers for 9 days. The microbiological assay of plasma level was unreliable at trimethoprim concentrations greater than 4 micrograms/ml, so results from an HPLC-assay are given. Steady state was present after 3 days. The plasma concentration peaked 1 to 4 h (mean 2.0 h) after the dose at a mean of 6.0 micrograms/ml (range 3.1-9.5 micrograms/ml); the minimum value was 1.5 micrograms/ml (range 0.6-2.9 micrograms/ml). The mean AUCss was 77 micrograms/ml X h and the mean plasma clearances was 67 and 74 ml/min on Days 8 and 9. Renal clearance was about 60% of the plasma clearance. The average plasma half life was 10.6 h (range 8.7-15.3 h). Thus, there was considerable interindividual variation in all pharmacokinetic parameters. 72 h after the last dose trimethoprim was detectable in plasma in only 1 of the 6 subjects. The minimum urinary concentration of trimethoprim during treatment was always well above (range 22 to 220 micrograms/ml) the MIC values for most urinary tract pathogens. Therefore, a daily dose of 300 mg trimethoprim results in a therapeutic concentration in urine at steady state that lasts throughout the dosing interval and in most subjects probably lasts also for a further 24 h. Trimethoprim administration raised mean serum creatinine from 67 to 97 mumol/l, probably due to competitive inhibition of the tubular secretion of creatinine.

Coupling between renal tubular secretion and effect of bumetanide

The relationship between renal tubular secretion of bumetanide and its saluretic effect was studied in six healthy subjects before and after probenecid (1 gm IV). Bumetanide was determined in serum and urine by HPLC. Continuous intravenous infusion of bumetanide (200 micrograms/hr) gave an average diuresis at steady state of 15 +/- 3 ml/min. Corresponding plasma concentration, urinary excretion rate, and renal clearance of bumetanide averaged 14.3 +/- 2.3 ng/ml, 64 +/- 31 micrograms/30 min, and 145 +/- 59 ml/min. After probenecid there was a marked change in bumetanide kinetics. Average plasma concentration rose to 41.7 +/- 8.1 ng/ml, whereas renal clearance and urinary excretion rate fell to 15.1% and 29.5% of control. There was also a concomitant decrease in diuresis and saluresis to 47% and about 40% of control. Probenecid also reduced the renal clearance of para-aminohippurate and inulin to 67% and 75% of control. Since the fractional water and sodium chloride excretion was also reduced about 33% and 42%, it is concluded that a large part of the diuretic effect of bumetanide depends on its active tubular secretion. As with furosemide and piretanide, bumetanide diuresis is elicited from the luminal side of the human nephron.

Renal tubular secretion of piretanide and its effects on electrolyte reabsorption and tubuloglomerular feedback mechanism

Piretanide [HOE 118; 4-phenoxy-3-(1-pyrrolidinyl)-5-sulfamoxylbenzoic acid] is a new diuretic with a saluretic effect similar to that of furosemide. The present experiments were undertaken to investigate if transport of piretanide into the tubular lumen determines the diuretic response and what effect piretanide has on the tubuloglomerular feedback control and loop of Henle electrolyte transport. To study the first question, five healthy subjects were investigated. Piretanide, inulin and p-aminohippuric acid were continuously infused. After equilibration, 1 g of probenecid was given which reduced the tubular secretion of piretanide to one-sixth of control level. The reduction in diuresis was 41.4% while it was 59.5, 63.9 and 45.8% for the urinary excretion of chloride, sodium and potassium, respectively. In a second series of experiments in rats a proximal tubular stop-flow pressure response at increased distal delivery of fluid was measured when Ringer's solution, Ringer's solution plus furosemide (10(-4) M) or bumetanide (5 X 10(-5) M) or piretanide (10(-4) M and 5 X 10(-5) M) was added to the tubular perfusion solution. The results indicate that the feedback could be completely blocked by any of these diuretics. The fluid absorption in the loop of Henle was studied in separate experiments and the addition of piretanide (10(-4) M) greatly reduced chloride and absolute fluid absorption from this nephron segment. The present results indicate that tubular secretion of piretanide is important for the diuretic response and that piretanide inhibits the fluid absorption in the loop of Henle and the tubuloglomerular feedback control which would otherwise blunt the diuretic response with a reduction in glomerular filtration rate.

Determinants of access of diuretics to their site of action

For consideration of the determinants of access of diuretics to their site of action to be meaningful, one must understand molecular modes of action of diuretics and the anatomic site of effect along the nephron in addition to determinants of the renal handling of diuretics. Although the molecular mode of action is known for a number of drugs, such as the inhibition of carbonic anhydrase by acetazolamide, that for loop diuretics remains obscure. Sites of diuretic action along the nephron have been well delineated through collation of results from in vitro and in vivo techniques in a variety of species. Loop diuretics clearly block chloride reabsorption throughout the thick ascending limb of the loop of Henle. Access of diuretics to their renal tubular sites of action varies among drugs. Important determinants are plasma protein binding, active tubular secretion, nonionic diffusion, and intrarenal metabolism.

Diuretic effect and pharmacokinetics of tizolemide in subjects with normal and decreased renal function

Tizolemide, a new sulphonamide diuretic, has alkaline properties and is cleared by a tubular transport system which differs from the PAH-excreting system which transports thiazide diuretics. The effect of this drug on the excretion of sodium and other electrolytes, and its pharmacokinetics, were evaluated in 5 healthy volunteers and in 10 patients with renal disease who had GFRs ranging from 5-98 ml/min. The saluretic effect of tizolemide was compared with that of placebo. The increase in sodium and chloride excretion after a single dose of 50 mg i.v. was clearly dependent on residual renal function but could be observed in all except one patient. It remains to be assessed whether a full diuretic effect can be achieved in patients with renal insufficiency if higher doses are used. The plasma half-life was 3.0 hours in healthy subjects but increased in patients with renal insufficiency to a maximum of 52 hours. In normal subjects total plasma clearance (611 ml/min) mainly depended on the renal clearance (564 ml/min) which decreased in proportion to GFR, whereas non-renal clearance remained unchanged. The large apparent volume of distribution of the drug (166 l/1.73 m2 BSA) did not increase significantly in uremia. Clinical trials with this drug in patients with reduced renal function must take into account the expected prolongation of its half-life.

Total serum IgE in uremia and after renal transplantation

Uremic patients on maintenance hemodialysis, but without clinical evidence of atopy or diabetes mellitus, had serum levels of total IgE significantly lower than in healthy controls matched for age and sex. Patients with uremia due to diabetic nephropathy had higher IgE levels than the reference group. No correlation was found between total IgE levels and length of dialysis treatment. After renal transplantation, the IgE levels decreased on average to 31% of the pretransplant values over a 60-day observation period. Bacterial or viral infections or episodes of kidney rejection had no apparent influence on the IgE synthesis in the patients with transplant. No correlation was detectable between pretransplant IgE levels and six-month survival of the kidney graft. The low IgE concentrations in uremia are suggested to reflect altered T-cell regulation of the IgE production. The raised IgE levels in diabetic patients could not be explained by specific reagins against insulin, but may have reflected an influence of abnormal carbohydrate metabolism on IgE synthesis. The fall in IgE levels following transplantation is proposed to be attributable to the combined corticosteroid-azathioprine treatment.

Renal tubular secretion and effects of chlorothiazide, hydrochlorothiazide and clopamide: a study in the avian kidney

The relationship between renal tubular secretion and saluretic effects of two thiazides (chlorothiazide and hydrochlorothiazide) and clopamide was studied using a modified Sperber technique. The distribution of carbonic anhydrase in the avian kidney was studied by a histochemical method. The modified Sperber technique allows an absolute estimation of the tubular excretion efficiency of a substance, as determined by its True Tubular Excretion Fraction (TTEF). The TTEF values were for chlorothiazide 59%, hydrochlorothiazide 22% and clopamide 10%. Thus, they were all actively secreted by renal tubular cells; most likely through organic anion transport since novobiocin markedly reduced the TTEF values. After infusion of the diuretics into the renal portal system on one side there was only a small ipsilateral excess natriuresis and chloruresis, in spite of their different tubular excretion efficiencies. For hydrochlorothiazide, and especially for chlorothiazide the saluretic effect therefore appears to be largely independent of the tubular fluid concentration of the diuretic and primarily evoked from the peritubular side of the avian nephron. This is a sharp contrast to the primarily luminally induced saluretic effects of furosemide, ethacrynic acid and piretanide. Only chlorothiazide caused an ipsilateral excess excretion of potassium and bicarbonate, probably due to inhibition of carbonic anhydrase since similar effects were seen after acetazolamide. This effect was coupled to tubular secretion of the diuretic, and probably reflects an inhibition of carbonic anhydrase in cortical distal tubules, where the enzyme is present in the apical region of most cells and could be reached by chlorothiazide present in the tubular fluid.

Effects of bendroflumethiazide on urate metabolism during treatment of patients with renal stones

Treatment with bendroflumethiazide (2.5 mg, twice daily with potassium supplements) in 63 patients with calcium-containing renal stones for a minimum period of 1 year (average duration of treatment 2.6 years) increased the serum urate values in all patients with an average of 90 mumol./l. (conversion factor: 1 mmol. urate = 183 mg.). Despite this the mean urinary urate excretion was unchanged. In the individual patient a systematic effect of therapy was evident since in patients with low pretreatment values the thiazide increased the urate output while in those with the highest levels before therapy it caused a reduction. In most patients there was a reduction of the urate clearance during therapy, which was most evident in those with the highest pretreatment clearance values. In patients with incomplete types of renal acidification defects the same effects were seen on urate metabolism during thiazide treatment as in the other, idiopathic, stone formers. Although the possible role of urate in calcium stone formation has not been definitely settled this study shows that thiazides do not cause hyperuricosuria and hence their beneficial effects on calcium excretion are not counteracted.