Localization of diuretic effects along the loop of Henle: an in vivo microperfusion study in rats.
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In order to clarify the effects on sodium reabsorption in the loop of Henle of methazolamide (a carbonic anhydrase inhibitor), chlorothiazide and the loop diuretics frusemide and bumetanide, superficial loops were perfused in vivo in anaesthetized rats and the individual diuretics were included in the perfusate. Differentiation between effects in the pars recta and in the thick ascending limb of Henle (TALH) was achieved by comparing responses to the diuretics when using a standard perfusate, designed to mimic native late proximal tubular fluid, and a low-sodium perfusate, designed to block net sodium reabsorption in the pars recta. With the standard perfusate, methazolamide caused decreases in sodium reabsorption (J(Na)) and water reabsorption (J(V)); with the low-sodium perfusate, a modest effect on J(Na) persisted, suggesting that carbonic anhydrase inhibition reduces sodium reabsorption in both the pars recta and the TALH. The effects of chlorothiazide were very similar to those of methazolamide with both the standard and low-sodium perfusates, suggesting that chlorothiazide also inhibits sodium reabsorption in the pars recta and TALH, perhaps through inhibition of carbonic anhydrase. With the standard perfusate, both frusemide and bumetanide produced the expected large decreases in J(Na), but J(V) was also lowered. With the low-sodium perfusate, the inhibitory effects of the loop diuretics, particularly those of frusemide, were substantially reduced, while net potassium secretion was found. These observations indicate that a significant component of the effect of frusemide (and possibly of bumetanide) on overall sodium reabsorption is located in the pars recta, and that loop diuretics induce potassium secretion in the TALH. (+info)
The acute effect of chlorothiazide on serum-ionized calcium. Evidence for a parathyroid hormone-dependent mechanism.
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The acute effects of chlorothiazide (CTZ) on total (TSCA) and ionized (SCA-plus 2) serum calcium concentrations were studied in three groups of people: (a) eight subjects with normal parathyroid function; (b) six patients with hypoparathyroidism; and (c) two patients with hyperparathyroidism. Most subjects were studied on four occasions; at least 3 days intervened between studies on an individual subject. During each experiment the subject received an i.v. influsion of 5% dextrose in water at 1 ml/min from 8 a.m. to 4 p.m. Additions to the infusions were (a) none; (b) CTZ to deliver 3.33 mg/kg/h; (c) parathyroid extract to deliver 1 U/kg/h; or (d) both CTZ and parathyroid extract at the rates previously indicated. CTZ, when used, was added to the infusion at 10 a.m., parathyroid extract at 8 a.m. When CTZ was infused, the diuretic-induced losses of Na and water were replaced by i.v. infusion. In normal subjects 2 h after the start of CTZ infusion, there was a transient increase in SCA-plus 2 which coincided in time of day with a transient decrease in SCA-plus 2 in control experiments. At that time of day SCA-plus 2 was 4.18 plus or minus 0.12 mg/100 ml in control experiments and 4.56 plus or minus 0.08 in experiments with CTZ, P smaller than 0.025. The corresponding values for (TSCA) were 9.32 plus or minus 0.15 and 9.80 plus or minus 0.30, P smaller than 0.01. Such differences were not observed in the group with hypoparathyroidism. In the two patients with hyperparathyroidism, CTZ produced sustained increases in TSCA and SCA-plus 2. In normal subjects and those with hypoparathyroidism, CTZ plus parathyroid extract infusion resulted in sustained increases in both SCA-plus 2 and TSCA throughout the periods of observation when compared to experiments in which only parathyroid extract was infused, P smaller than 0.01 in all instances. The results suggest that the acute hypercalcemic action of CTZ requires the presence of circulating parathyroid hormone. (+info)
Clarification of the site of action of chlorothiazide in the rat nephron.
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The saluretic effect of the thiazide diuretics has been attributed to inhibition of sodium reabsorption in the distal nephron of the kidney. Recent micropuncture studies have shown, however, that chlorothiazide administration can also inhibit sodium reabsorption in the proximal convolution. To clarify the site of the saluretic effect of chlorothiazide, these micropuncture studies examined the effect of chlorothiazide on chloride transport in the nephron. The effect of chlorothiazide on chloride transport was studied because chlorothiazide's effectiveness as a saluretic is largely due to its ability to enhance sodium chloride excretion; if only changes in sodium transport are examined, it would be then difficult to determine if sodium as bicarbonate or as chloride is affected, since chlorothiazide can inhibit carbonic anhydrase. One group of rats was studied before and after 15 mg/kg per h chlorothiazide. For comparison, another group of rats was studied before and after 2 mg/kg per h benzolamide, a carbonic anhydrase inhibitor. Fractional chloride delivery from the proximal tubule was similarly increased in both groups from 59.4 to 71.0% by chlorothiazide administration, Pless than 0.0001, and from 54.3 to 68.2% by benzolamide administration, P less than 0.001. The increased delivery very of chloride from the proximal tubule was largely reabsorbed before the early distal tubule as fractional chloride delivery to this site increased only from 5.08 to 7.40% after chlorothiazide administration, P less than 0.001, and from 4.50 to 6.29% after benzolamide administration, P less than 0.01. Benzolamide had no effect on chloride reabsorption in the distal convoluted tubule. However, chlorothiazide administration resulted in a marked decrease in distal tubular chloride reabsorption, the fraction of filtered chloride present at the late distal tubule incresing from 1.24 to 6.25%, P less than 0.001. Fractional chloride excretion in the urine increased from 0.29 to 3.44%, P less than 0.001, after chlorothiazide, but did not change after benzolamide. The influence of chlorothiazide on proximal chloride transport presumably is related to its ability to inhibit renal carbonic anhydrase. However, it is not the effect of chlorothiazide in the proximal convolution but rather its effect in the distal convoluted tubule which is primarily responsible for its ability to be an effective saliuretic. (+info)
Mechanism of calcium transport stimulated by chlorothiazide in mouse distal convoluted tubule cells.
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Thiazide diuretics inhibit Na+ and stimulate Ca2+ absorption in renal distal convoluted tubules. Experiments were performed on immortalized mouse distal convoluted tubule (MDCT) cells to determine the mechanism underlying the dissociation of sodium from calcium transport and the stimulation of calcium absorption induced by thiazide diuretics. Control rates of 22Na+ uptake averaged 272 +/- 35 nmol min-1 mg protein-1 and were inhibited 40% by chlorothiazide (CTZ, 10(-4) M). Control rates of 36Cl- uptake averaged 340 +/- 50 nmol min-1 mg protein-1 and were inhibited 50% by CTZ. CTZ stimulated 45Ca2+ uptake by 45% from resting levels of 2.86 +/- 0.26 nmol min-1 mg protein-1. Bumetanide (10(-4) M) had no effect on 22Na+, 36Cl-, or 45Ca2+ uptake. Control levels of intracellular calcium activity ([Ca2+]i) averaged 91 +/- 12 nM. CTZ elicited concentration-dependent increases of [Ca2+]i to a maximum of 654 +/- 31 nM at 10(-4) M. CTZ reduced intracellular chloride activity ([Cl-]i), as determined with the chloride-sensitive fluorescent dye 6-methoxy-N-(3-sulfopropyl)quinolinium. The chloride channel blocker 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB, 10(-5) M) abolished the effect of CTZ on [Cl-]i. NPPB also blocked CTZ-induced increases of 45Ca2+. Resting membrane voltage, measured in cells loaded with the potential-sensitive dye 3,3'-dihexyloxacarbocyanine iodide [DiOC6(3)], averaged -72 +/- 2 mV. CTZ hyperpolarized cells in a concentration-dependent and reversible manner. At 10(-4) M, CTZ hyperpolarized MDCT cells by 20.4 +/- 7.2 mV. Reduction of extracellular Cl- or addition of NPPB abolished CTZ-induced hyperpolarization. Direct membrane hyperpolarization increased 45Ca2+ uptake whereas depolarization inhibited 45Ca2+ uptake. CTZ-stimulated 45Ca2+ uptake was inhibited by the Ca2+ channel blocker nifedipine (10(-5) M). We conclude that thiazide diuretics block cellular chloride entry mediated by apical membrane NaCl cotransport. Intracellular chloride, which under control conditions is above its equilibrium value, exits the cell through NPPB-sensitive chloride channels. This decrease of intracellular chloride hyperpolarizes MDCT cells and stimulates Ca2+ entry by apical membrane, dihydropyridine-sensitive Ca2+ channels. (+info)
Fluid transport in a cultured cell model of kidney epithelial cyst enlargement.
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Madin-Darby canine kidney (MDCK) cells, when seeded into collagen gel, from polarized, spherical, epithelial cysts, which grow by a process involving fluid secretion and cell proliferation. These cysts are a useful model for understanding the dynamics of cyst enlargement in renal cystic disease. The hypothesis that MDCK cyst fluid secretion depends upon chloride secretion was tested, and a cell model for this process is presented here. Lumen and epithelial cell volumes were measured by video microscopy in acute experiments. Fluid absorption (-0.073 +/- 0.007 microliters.h-1.cm-2; N = 8) was observed when cysts were superfused with unsupplemented Dublecco's modified Eagle's medium at 36 to 37 degrees C. Fluid secretion (0.221 +/- 0.0016 microliters.h-1.cm-2; N = 25) was seen when 1 mM dibutyryl cAMP plus 0.1 mM 3-isobutyl-1-methylxanthine were added to the superfusate. cAMP-induced fluid secretion was significantly inhibited by basolateral 1 mM ouabain, 0.1 mM furosemide, or 1 mM amiloride. It was not significantly affected by 1 mM chlorothiazide, 0.01 mM bumetanide, or 0.1 mM acetazolamide in the presence of normal bicarbonate/CO2. In the nominal absence of bicarbonate/CO2 fluid secretion was 18% of control. Vasopressin-induced fluid secretion was significantly inhibited by pretreatment of cysts with 0.1 mM 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS). Cyst cell shrinkage in isosmotic chloride-free Ringer's solution (chloride replaced by gluconate) was inhibited by 0.1 mM basolateral DIDS. The results suggest that chloride-bicarbonate exchange in the basolateral membrane of MDCK cyst epithelial cells plays a critical role in cyst fluid secretion. (+info)
Action of chlorothiazide on the distribution excretion and hypotensive effect of pempidine in man.
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When chlorothiazide is given to hypertensive patients who are receiving pempidine a rise in plasma pempidine concentration occurs and this is proportionately greater than the additional fall in blood pressure. After pempidine has been added to human whole blood in vitro or in vivo the ratio of the pempidine concentration in the red cells to that in the plasma falls in the course of 1 hr from an initial value greater than 2 to about 1.2. If chlorothiazide is present also, however, the ratio remains constant at 0.7. Changes in the plasma pempidine concentration in vivo probably result from the binding of pempidine to plasma protein in the presence of chlorothiazide. This has been observed in vitro by a dialysis technique. (+info)
A comparison of the use of Aldactone and Aldactone A in the treatment of hepatic ascites.
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In eight patients with cirrhosis and stable ascites controlled on chlorothiazide and spironolactone, a small particle preparation of spironolactone (Aldactone A) was as effective, at one quarter the dosage, as conventional spironolactone (Aldactone). Plasma spironolactone metabolite levels and urinary excretion of spironolactone metabolite were equivalent with both preparations. The variable dosage requirement of spironolactone in patients with cirrhosis and ascites is discussed in relation to these observations. (+info)
Dangers in the use of some potent drugs.
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The chief dangers reported with some common drugs are reviewed. Hazards of antibiotic therapy include: the increasing incidence of sensitization to penicillin with occasional anaphylactic reactions; aplastic anemia with chloramphenicol, and the poor tolerance of infants for chloramphenicol; staphylococcal enterocolitis; unnecessary "prophylactic" use of antibiotics. Thiazide diuretics may precipitate potassium depletion, skin reactions, pancreatitis, blood dyscrasias, gout, diabetes mellitus and hepatic coma. Reserpine can increase gastric acidity, induce mental depression, and when used with digitalis lead to ventricular premature beats. Hydralazine may aggravate angina pectoris, cause tachycardia, and bring about a syndrome resembling disseminated lupus erythematosus. Guanethidine may result in loose stools, impotence, and postural hypotension. Hazards of phenothiazines include jaundice, parkinsonian states and tremors, convulsions, hypotension, and blood dyscrasias. The butanediols have numerous side effects including gastrointestinal, cutaneous and hypotensive reactions. Prolonged corticosteroid therapy introduces a new danger in surgical treatment. The progesterone-like drugs may induce masculinization of the female fetus. (+info)