Jochen Kipnowski

Digoxin-Like Immunoreacting Substance(s) in the Serum of Patients with Chronic Uremia

In patients with chronic uremia we have previously demonstrated a significant inhibition of the Na-K-ATPase enzyme which represents the specific receptor protein for cardiac glycosides. Since an endogenous inhibitor of this enzyme was previously shown to react with a digoxin antibody, in the present study we determined digoxin-like immunoreacting activity(ies) (DLIA) by a radioimmunoassay in 15 nondialyzed patients with chronic renal failure. In native serum, DLIA ranged from 0 to 1.70 ng/ml and was unrelated to the degree of renal failure. After gel filtration of serum, DLIA exclusively eluted in the small molecular weight salt (FIII) and post-salt (FIV) fractions and averaged 0.22 +/- 0.04 and 0.20 +/- 0.05 ng/ml in fractions III and IV, respectively. Total activities ranged from 0.11 to 0.88 ng/ml with a mean of 0.42 +/- 0.06 ng/ml and closely correlated with the degree of renal impairment (p less than 0.001). The results confirm the presence of small molecular weight digoxin-like immunoreacting substance(s) in uremic serum. The variable activities in native serum and the lack of correlation between the degree of renal failure and DLIA in serum fraction IV previously shown to possess the Na-K-ATPase-inhibiting activity, however, indicate that DLIA may not reflect specifically the endogenous sodium pump inhibitor and that unspecific binding to this digoxin antibody of uremic toxins or other endogenous compounds, such as steroids other than aldosterone, may have occurred.

Prostaglandins Participate in the Regulation of NaCl Absorption in the Diluting Segments of the Nephron in vivo: Effects of Furosemide

Various studies point to a role of the renal prostaglandin (PG) system in the regulation of renal NaCl excretion. In the present experiments, distal delivery of proximal tubular fluid (DD) [CH20 + CC1)/GFR x 100] and distal fractional chloride absorption (DFAC1) [CH20/(CH20 + CC1)] were studied in 6 healthy volunteers undergoing sustained water diuresis. Studies of renal function were performed during intravenous infusion of hypotonic (0.45%) saline and during additional treatment with indomethacin, furosemide and furosemide plus indomethacin. Hypotonic saline was infused at increasing rates of 0.09, 0.18, and 0.36 ml min-1 kg-1 body weight each for a 45-min period. DD over all three clearance periods averaged 8.27 +/- 0.71 ml min-1 100 ml-1 glomerular filtration rate (GFR) during saline infusion alone and was unchanged by indomethacin (8.09 +/- 0.63 ml min-1 100 ml-1 GFR). DFAC1 averaged 0.79 +/- 0.02 during saline and significantly increased to 0.87 +/- 0.01 (p less than 0.002) during concomitant indomethacin treatment. Increased NaCl absorption in the diluting segment during indomethacin was paralleled by a decrease in urinary excretion of chloride (UC1V) from 221 +/- 29 during control to 124 +/- 19 muEq/min (p less than 0.025) and in urinary excretion of PGE2 (UPGE2V) from 1.45 +/- 0.12 to 0.51 +/- 0.09 pmol/min (p less than 0.025). Furosemide increased UPGE2V to 2.94 +/- 0.34 pmol/min (p less than 0.05) and UC1V to 2,590 +/- 128 muEq/min (p less than 0.001). This effect was associated with an increase in DD to 26.70 +/- 1.33 ml min-1 100 ml-1 GFR (p less than 0.001) and a decrease in DFAC1 to 0.19 +/- 0.02 (p less than 0.001). Neither DD and DFAC1 nor UC1V were altered during furosemide+indomethacin as compared to furosemide in spite of a marked suppression of UPGE2V to 0.56 +/- 0.13 pmol/min. Our results support the concept that renal PG participate in the regulation of NaCl absorption in the diluting segments of the nephron. Furthermore, the tubular effects of furosemide appear not to be mediated by the PG system.

Combined treatment of severe essential hypertension with the new angiotensin converting enzyme inhibitor ramipril

Ramipril is a newly synthesized angiotensin converting enzyme inhibitor without a sulfhydryl group in the molecule but with a prolonged duration of action. Efficacy, tolerance and safety of this drug were evaluated in 10 patients with severe essential hypertension. After a treatment period of at least 4 weeks with the conventional antihypertensive drug combination of a diuretic and a beta-blocking agent with the vasodilator dihydralazine, their systolic and diastolic blood pressures averaged 161 +/- 6 and 111 +/- 2 mm Hg, respectively. Because diastolic blood pressure during this drug regimen was still greater than 105 mm Hg in all patients, the patients received ramipril initially at single daily doses of 5 mg in addition to their previous medication. The first dose of 5 mg ramipril resulted in a moderate but significant decrease in systolic and diastolic blood pressure in 9 of the 10 patients to 142 +/- 5 and 104 +/- 4 mm Hg (p less than 0.01), respectively, between 3 and 6 hours after drug administration. In 1 patient blood pressure was unresponsive to ramipril and 1 patient complained of nausea and vomiting within the first week of treatment with ramipril. Within the following 8-week treatment period with a once-daily intake of 5 or, if necessary, 10 mg of ramipril, diastolic blood pressure normalized in the remaining 8 patients to less than 90 mm Hg. Systolic and diastolic blood pressure averaged 130 +/- 5 and 83 +/- 2 mm Hg, respectively, at the end of the 8-week treatment period with ramipril. Severe hypotension and reflex tachycardia were not observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandins and renal NaCl excretion in healthy human subjects: effects of prostaglandin synthesis inhibition with indomethacin.

SummaryThe effect of a single oral dose of 75 mg of indomethacin on renal function and urinary excretion of prostaglandin (PG) E2 was investigated in six healthy volunteers. In the absence of changes in GFR, indomethacin significantly reduced urinary excretion of sodium and chloride for 12 h with a return to control values afterwards. This effect on the renal excretory function was closely paralleled by a decrease in urinary excretion of PGE|12|0 which also returned to control values after 12 h. In a second series of experiments, inhibition of PG synthesis was performed in healthy volunteers during sustained water diuresis to determine the tubular site of altered NaCl absorption using clearance methods. Again, indomethacin induced a significant suppression of urinary excretion of sodium, chloride and potassium without changes in GFR or urinary excretion of phosphate. Indomethacin treatment had no effect on the delivery of chloride beyond the proximal tubule to the distal tubules (distal delivery) but significantly increased the distal fractional absorption of chloride (DFACl). In a third series of experiments, the effect of furosemide on GFR and tubular NaCl absorption was studied without and with concomitant administration of indomethacin. Furosemide induced an almost twelvefold increase in the urinary excretion of sodium and chloride, an approximately threefold increase in urinary excretion of potassium and a significant increase in urinary phosphate excretion. Furosemide also increased distal delivery and decreased DFACl and also increased urinary excretion of PGE2. Concomitant indomethacin treatment significantly suppressed urinary excretion of PGE2 but did not affect any of the furosemide induced changes in renal function. Our results support the concept that PG participate in the regulation of renal NaCl excretion and suggest that the diluting segments of the nephron may be the site of action of renal PG. Furthermore, furosemide stimulates renal synthesis of PGE2 but the tubular effects of this diuretic appear not to be mediated by the renal PG system.ZusammenfassungAn sechs gesunden Versuchspersonen wurde die Wirkung einer oral verabreichten Einzeldosis von 75 mg Indometacin auf die Nierenfunktion und die Urinausscheidung von Prostaglandin (PG) E2 untersucht. Indometacin bewirkte eine signifikante Reduktion der NaCl Ausscheidung über einen Zeitraum von 12 h ohne gleichzeitige Wirkung auf die GFR. Diese Wirkung auf die exkretorische Nierenfunktion war von einer gleichzeitigen Abnahme der Urinausscheidung von PGE2 begleitet, welche ebenfalls nach 12 h wieder auf Kontrollwerte anstieg. In einer zweiten Versuchsserie wurde die Wirkung einer Indometacingabe auf proximale und distale Tubulusfunktion während Wasserdiurese mittels Clearance-Methoden ermittelt. Dabei kam es nach Indometacingabe wiederum zu einer signifikanten Reduktion der Urinausscheidung von Chlorid, Natrium und Kalium ohne Änderungen der GFR oder der Urinausscheidung von Phosphat. Die Indometacingabe hatte keinen Effekt auf die Chloridmenge, die den distalen Tubulus erreicht (distal delivery), führte jedoch zu einem signifikanten Anstieg der distalen fraktionellen Absorption von Chlorid (DFACl). In einer dritten Versuchsserie wurde die Wirkung von Furosemid auf die GFR und die tubuläre NaCl Absorption ohne und mit gleichzeitiger Gabe von Indometacin untersucht. Nach Gabe von Furosemid kam es zu einem fast zwölffachen Anstieg der Urinausscheidung von Natrium und Chlorid, einem etwa dreifachen Anstieg der Urinausscheidung von Kalium und einem signifikanten Anstieg der Urinausscheidung von Phosphat. Weiterhin kam es nach Furosemidgabe zu einem signifikanten Anstieg der “distal delivery”, einer Abnahme der DFACl und einem Anstieg der Urinausscheidung von PGE2. Unter gleichzeitiger Gabe von Indometacin kam es zu einer signifikanten Abnahme der Urinausscheidung von PGE2 ohne daß die Furosemid-induzierten Änderungen der exkretorischen Nierenfunktion dadurch verändert wurden. Unsere Ergebnisse legen eine Rolle des endogenen PG-Systems bei der Regulation der renalen NaCl Ausscheidung nahe und lokalisieren eine solche Wirkung in das Verdünnungssegment des distalen Tubulus. Furosemide vermag die renale Synthese von PGE2 zu stimulieren aber die tubuläre Wirkung dieses Diuretikums scheint nicht über das renale PG System vermittelt zu werden.

[Hepato-renal syndrome (author's transl)].

SummaryThe hepato-renal syndrome is defined as potentially reversible functional renal failure associated with acute fulminant hepatitis or, more often, with advanced chronic liver failure. It is characterized by oliguria, azotemia, retention of sodium and water with formation of ascites, and hyponatremia. While urinary sodium concentration of less than 10 mEq/l reflects intact tubular sodium absorption, the kidney lacks the ability for adequate free-water generation. This condition must be separated from specific renal diseases which may arise during the course of intraor extrahepatic diseases and which must be classified accordingly. Pathophysiological aspects of the hepato-renal syndrome include hemodynamic factors, such as changes in intrarenal blood flow distribution in the presence of elevated intrarenal and reduced peripheral vascular resistance. The functional relationship of vasoconstrictor, sodium retaining, and antidiuretic hormones (e.g., renin-angiotensin, aldosterone, and vasopressin) to vasodilator, diuretic, and natriuretic hormonal factors (e.g., prostaglandins, kinins, and natriuretic hormone) may be altered as well. Finally, a pre- and intrahepatic spillover resulting in decreased endotoxin clearance must be considered. Due to the lack of understanding of their complex interactions, so far pharmacological and therapeutic approaches remained ineffective to correct at least some of these factors. Today, recovery from hepato-renal syndrome will, therefore, mainly depend on the course of the underlying liver disease.ZusammenfassungDas hepatorenale Syndrom wird als potentiell reversibles funktionelles Nierenversagen definiert, das bei fortgeschrittener Leberinsuffizienz auftritt und durch Oligurie, Azotämie, renale Natrium-und Wasserretention sowie Hyponatriämie charakterisiert ist. Die auf weniger als 10 mÄq/l reduzierte Natrium-Konzentration im Urin spricht für eine intake tubuläre Natrium-Resoprtion, während die renale Freiwasser-Bildung eingeschränkt ist. Sonstige im Verlauf von Leber- oder Gallenwegserkrankungen auftretende spezifische Nierenschädigungen dürfen nicht dem Begriff des hepatorenalen Syndroms zugeordnet, sondern müssen als solche gekennzeichnet werden. Pathophysiologisch sind hämodynamische Faktoren, wie Änderungen der intrarenalen Blutstromverteilung bei erhöhtem intrarenalem und vermindertem peripherem Gefäßwiderstand wirksam. Weiterhin dürfte ihm eine Störung des funktionellen Gleichgewichts von vasokonstriktorischen, natrium-retinierenden und antidiuretischen hormonellen Faktoren (z.B. Renin-Angiotensin, Aldosteron und Vasopressin) zu vasodilatorisch, diuretisch und natriuretisch wirkenden Hormonen (z.B. Prostaglandine, Kinine und Natriuretisches Hormon) zugrunde liegen. Schließlich bedingt das prä- und intrahepatische “Spillover” eine unzureichende Endotoxin-Clearance. Bisherige pharmakologische Interventionen zur Beseitigung einzelner Störungen ebenso wie klinischtherapeutische Maßnahmen blieben nicht zuletzt wegen ungenügender Kenntnis der relativen Bedeutung dieser Faktoren erfolglos. Die Prognose des Patienten mit hepatorenalem Syndrom wird daher heute noch vor allem vom Verlauf der zugrundeliegenden Lebererkrankung bestimmt.The hepato-renal syndrome is defined as potentially reversible functional renal failure associated with acute fulminant hepatitis or, more often, with advanced chronic liver failure. It is characterized by oliguria, azotemia, retention of sodium and water with formation of ascites, and hyponatremia. While urinary sodium concentration of less than 10 mEq/l reflects intact tubular sodium absorption, the kidney lacks the ability for adequate free-water generation. This condition must be separated from specific renal diseases which may arise during the course of intra-or extrahepatic diseases and which must be classified accordingly. Pathophysiological aspects of the hepa-to-renal syndrome include hemodynamic factors, such as changes in intrarenal blood flow distribution in the presence of elevated intrarenal and reduced peripheral vascular resistance. The functional relationship of vasoconstrictor, sodium retaining, and anti-diuretic hormones (e.g., renin-angiotensin, aldosterone, and vasopressin) to vasodilator, diuretic, and natriuretic hormonal factors (e.g., prostaglandins, kinins, and natriuretic hormone) may be altered as well. Finally, a pre- and intrahepatic spillover resulting in decreased endotoxin clearance must be considered. Due to the lack of understanding of their complex interactions, so far pharmacological and therapeutic approaches remained ineffective to correct at least some of these factors. Today, recovery from hepato-renal syndrome will, therefore, mainly depend on the course of the underlying liver disease.

Effects of trifluoperazine and verapamil on the hydro-osmotic response to antidiuretic hormone in the urinary bladder of the toad

SummaryTo investigate the role of the intracellular calcium-calmodulin complex in the hydro-osmotic response to antidiuretic hormone (ADH), the effects of trifluoperazine (TFP), a well-established inhibitor of calmodulinmediated functions, and of verapamil (V), a calcium entry blocker, were examined in the urinary bladder of the toad, a model for the late distal tubule and the collecting duct of the mammalian nephron. Preincubation of the hemibladders with TFP at serosal concentrations of 10−5 and 10−4M was without effect on basal water flow but markedly reduced the maximal hydroosmotic response to ADH (50 mU/ml) in a dose-dependent manner as compared to control hemibladders (23.60±1.23 vs. 42.17±4.18mg/min per hemibladder (10−5M TFP) and 5.43±0.59 vs. 52.50±4.67mg/min per hemibladder (10−4M TFP). This inhibitory effect of TFP on the ADH-stimulated osmotic water flow persisted in the presence of naproxen (10−5M), a known inhibitior of prostaglandin synthesis. The hydro-osmotic response to cyclic adenosine 3′,5′ monophosphate (cAMP, 10−3M) was also significantly reduced in TFP-pretreated tissues (11.68 ± 1.84 vs. 32.83 ± 3.14 mg/min per hemibladder), suggesting a post-cAMP inhibitory effect of TFP. V (10−4M) had no effect on basal water flow but significantly reduced the hydro-osmotic effect of 50 mU/ml ADH (15.17 ± 1.05 vs. 38.00 ± 3.39 mg/min per hemibladder). In contrast, cAMP-stimulated osmotic water flow was significantly stimulated in V-treated tissues (48.07 ± 1.95 vs. 27.13 ± 1.50 mg/min per hemibladder). These results are consistent with the view that the intracellular calcium-calmodulin complex modulates the action of ADH on osmotic water flow via a post-cAMP step. Blocking Ca2+-entry into the cell during ADH-stimulated osmotic water flow points to the role of calcium ions as modulators of the action of ADH in addition to the modulating effects of the calcium-calmodulin complex. However, the enhanced water flow response to cAMP in the presence of V suggests that the interaction of Ca2+-ions with the action of ADH occurs at a site prior to cAMP generation.

Tubular Effects of Atrial Extract and of Atriopeptin III in Conscious Rats

To investigate a tubular action of atrial natriuretic peptide (ANP), in the present study the effects of rat atrial extract (AE) and of synthetic rat atriopeptin III (AP III) were assessed in conscious rats during hypotonic saline infusion. Renal plasma flow (RPF) and glomerular filtration rate (GFR) were estimated by the clearances (C) of PAH and of endogenous creatinine, respectively. CPO4 was used as a marker of proximal tubular function. Distal delivery (DD) and distal fractional absorption of chloride (DFACl), a measure of solute absorption in the diluting segments, were calculated from CH2O and CCl. AE and AP III increased RPF in all groups of animals. Low doses of AP III (40 ng/100 g B.W.) significantly increased urine flow rate and CCl, whereas GFR, CNa, CPO4, and CK remained unaltered. The marked natriuresis at high doses of ANP was associated with a rise in GFR and in absolute and fractional CPO4 as well as an increase in DD and CK. AE and AP III (1 microgram/100 g B.W.) decreased DFACl from 0.94 +/- 0.03 and 0.87 +/- 0.03 to 0.80 +/- 0.07 (p less than 0.05) and 0.54 +/- 0.07 (p less than 0.01), respectively. Some of the effects on tubular reabsorptive capacity probably result from medullary wash-out which thereby contributes to the natriuresis by potentiating the rise in the filtered load of sodium at high ANP levels. In the absence of changes in GFR and CPO4, the tubular action of ANP is more accurately reflected by CCl which may result from decreased absorption in the medullary collecting tubule.

Effects of standard diuretics and RPH 2823 on transepithelial Na+ transport in isolated frog skin.

SummaryShort-circuit current (SCC) techniques were used to monitor the effects of various diuretic agents on Na+ transport in isolated frog skin, a model for the late distal tubule and the collecting duct of the mammalian kidney. Acctazolamide, hydrochlorothiazide, torasemide, and ethacrynic acid did not affect sodium transport (as indicated by the SCC) or transepithelial electrical resistance when added either to the apical (outer) or to the inner (basolateral, corial) bathing solution of the tissue. However, Na+ transport was sensitive to amiloride, the triamterene derivate dimethylamino-hydroxypropoxytriamterene (RPH 2823), and to furosemide. Whereas apical amiloride, and RPH 2823 induced a dose-dependent decrease in SCC and increase in transepithelial electrical resistance, apical furosemide resulted in a dose-dependent increase in SCC and a decrease in electrical resistance. None of the three diuretic agents caused a significant change in SCC when applied to the inner bathing Ringers solution. The small furosemide-induced decrease in resistance compared with the huge increase in SCC suggests that furosemide affects Cl− permeability as well as Na+ permeability. Evidence for this notion was achieved by the following findings: (a) The decrease in resistance after furosemide was more pronounced in tissues bathed in Cl−-free solutions compared with Cl−-containing solutions. (b) In contrast, SCC stimulation by apical furosemide is Cl−-ion independent, but strongly Na+-ion dependent. (c) SCC stimulation by furosemide is amiloride-sensitive. With respect to the onset, locus, and reversibility of action, it seems reasonable to assume that amiloride, RPH 2823, and furosemide all influence transepithelial Na+ transport by interacting with the Na+ channel or a regulator site of it within the apical membrane. The stoichiometry of the amiloride (RPH 2823)-receptor site interaction revealed Hill-coefficient(s) of less than 1, indicating a negative cooperativity among the receptor sites. The interaction between Na+ ions and amiloride or RPH 2823 displayed mixed competitive-noncompetitive inhibition. Taken together, these results support the hypothesis that amiloride and Na+ as well as RPH 2823 and Na+ may act at different loci on the apical entry mechanism inRana esculenta skin.