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At least 73 records · Page 4Linked to original sources

PubMed1994

Comparison of derivatization procedures for the determination of diuretics in urine by gas chromatography-mass spectrometry.

Three different GC-MS screening procedures, which use different ways of derivatization (methylation), are compared. In the first one, derivatization with iodomethane in acetone and a previous solid-liquid extraction is used; the second one is based on an extractive alkylation method using iodomethane in toluene (liquid-liquid extraction); and the last one is flash methylation by pyrolysis of tetraalkylammonium salts in the injector of the gas chromatograph using trimethylanilinium as the derivatization agent. The speed of the extraction, reproducibility and accuracy have been compared for 20 diuretics including the ones most often used in sports, such as bumetanide, ethacrynic acid, acetazolamide, dichlorphenamide, furosemide, hydroflumethiazide, hydrochlorothiazide and chlorthalidone; they have also been applied to the two uricosuric agents probenecid and benzbromarone.

Diuretics↗

PubMed1997

Structure and mechanism of carbonic anhydrase.

Carbonic anhydrase (CA; carbonate hydro-lyase, EC 4.2.1.1) is a zinc-containing enzyme that catalyzes the reversible hydration of carbon dioxide: CO2+ H2O<-->HCO3(-)+H+. The enzyme is the target for drugs, such as acetazolamide, methazolamide, and dichlorphenamide, for the treatment of glaucoma. There are three evolutionarily unrelated CA families, designated alpha, beta, and gamma. All known CAs from the animal kingdom are of the alpha type. There are seven mammalian CA isozymes with different tissue distributions and intracellular locations, CA I-VII. Crystal structures of human CA I and II, bovine CA III, and murine CA V have been determined. All of them have the same tertiary fold, with a central 10-stranded beta-sheet as the dominating secondary structure element. The zinc ion is located in a cone-shaped cavity and coordinated to three histidyl residues and a solvent molecule. Inhibitors bind at or near the metal center guided by a hydrogen-bonded system comprising Glu-106 and Thr-199. The catalytic mechanism of CA II has been studied in particular detail. It involves an attack of zinc-bound OH- on a CO2 molecule loosely bound in a hydrophobic pocket. The resulting zinc-coordinated HCO3- ion is displaced from the metal ion by H2O. The rate-limiting step is an intramolecular proton transfer from the zinc-bound water molecule to His-64, which serves as a proton shuttle between the metal center and buffer molecules in the reaction medium.

Animals↗

PubMed1990

Glaucoma in the dog and cat.

Conjunctivitis, mydriasis, corneal edema, lens luxation, buphthalmos, and blindness are caused by elevated IOP in the glaucomas. Primary glaucomas with a bilateral potential for development are noted in two cats and several dog breeds, with secondary glaucomas caused by uveitis and neoplasia common in the cat and dog. Tonometric evaluation is essential for the early diagnosis and management of glaucoma. Medical therapy of topical demecarium bromide and timolol maleate, with systemic dichlorphenamide, are recommended for general glaucoma maintenance therapy in dogs and cats. Transcleral cyclophotocoagulation will surgically reduce IOP in cases in which maximum medication has been reached.

Animals↗

PubMed2004

Carbonic anhydrase inhibitors are specific openers of skeletal muscle BK channel of K+-deficient rats.

Carbonic-anhydrase (CA) inhibitors are used in the treatment of hypokalaemic periodic paralysis (hypoPP) and related channelopathies but their mechanism of action is unknown. Patch-clamp experiments and molecular modeling investigations were performed to evaluate the mechanism of actions of CA inhibitors on skeletal muscle Ca2+-activated-K+ (BK) channel of K+-deficient rats used as animal model of hypoPP. CA inhibitors showing different degree of CA inhibition such as acetazolamide (ACTZ), dichlorphenamide (DCP), hydrochlorthiazide (HCT), etoxzolamide (ETX), methazolamide (MTZ), and bendroflumethiazide (BFT), which lacks inhibitory effects on CA enzymes, were tested in vitro on BK channels. The application of ACTZ, BFT, ETX, and DCP to excised patches activated the BK channel with potency: ACTZ(DE50=7.3x10(-6)M)>BFT(DE50=5.93x10(-5)M)>ETX(DE50=1.17x10(-4)M)>>DCP. In contrast, MTZ and HCT failed to activate the BK channel. Molecular modeling studies showed that the capability of CA inhibitors to open the BK channel was related to the presence in their structures of an intra-molecular hydrogen bond with calculated inter-atomic distances ranging between 1.82 A degrees and 3.01 A degrees and of an aromatic ring poor of electrons. ACTZ, BFT, ETX, and DCP showed these pharmacofores, while MTZ and HCT did not. Our data indicate that the activation of BK channel is a property of CA inhibitors that interact with the channel subunit/s and that this effect is not related to their capability to inhibit the CA enzymes.

Animals↗

PubMed2003

Generation and evaluation of a CYP2C9 heteroactivation pharmacophore.

Positive cooperativity (auto- and heteroactivation) of drug oxidation, a potential cause of drug interactions, is well established in vitro for cytochrome P450 (P450) 3A4 but to a much lesser extent for other drug-metabolizing P450 isoforms. Using a high throughput fluorescent-based CYP2C9 effector assay, we identified >30 heteroactivators from a set of 1504 structurally diverse compounds. Several potent heteroactivators of CYP2C9-mediated 7-methoxy-4-trifluoromethyl-coumarin metabolism are marketed drugs or endogenous compounds (amiodarone, niclosamide, liothyronine, meclofenemate, zafirlukast, estropipate, and dichlorphenamide, yielding 150% control reaction velocity at 0.04, 0.09, 0.5, 1, 1.2, 1.5, and 2.5 microM, respectively). Some heteroactivators are also known CYP2C9 substrates or inhibitors, suggesting potential multiple binding sites and substrate-dependent effects. v(150%), the concentration of effector giving 150% of control reaction velocity, was used as pharmacophore modeling parameter based on enzyme kinetic assumptions. The generated pharmacophore (training set: n = 36, v(150%) 0.04-150 microM) contains one hydrogen bond acceptor, one aromatic ring, and two hydrophobes. v(150%) values for 94% of the training set heteroactivators were predicted within 1 log unit for the residual (r [log observed v(150%)] versus [log predicted v(150%)] = 0.71; r2 0.50). The model also correctly identifies close to 70% of potent inhibitors (IC50 < 1 microM) as high-affinity CYP2C9 binders, suggesting that heteroactivators and inhibitors share some common structural CYP2C9 binding features, supporting the previously suggested hypothesis that CYP2C9 heteroactivators can bind within the active site.

Aryl Hydrocarbon Hydroxylases↗

PubMed1997

Microinjection studies on the effect of furosemide on the rat nephron.

The tubular site of furosemide (F) action was studied by the technique of diuretic microinjection (MIJ) into proximal tubules of the rat nephron. F was injected into the last proximal superficial loop of 51 proximal tubules, at the concentration of 3 x 10(-4) mol/l in an infusate that contained 14C-inulin. Collections were performed at the early distal tubule before and after MIJ. Single nephron filtration rate (SNGFR) remained unchanged, while the percent of filtered volume reabsorbed up to the site of collection was 85+/-2 before, 79+/-2% after MIJ, p < 0.005. The calculated concentration of F in the collected distal tubular fluid during the post-MIJ measurements averaged 3 x 10(-5) mol/l. This experiment was repeated by injecting F into the early proximal convolutions of 43 nephrons, while the collections were performed at the last proximal segments. In these studies of proximal volume absorption, SNGFR was 34+/-3 before, 35+/-4 nl/min after F (p > 0.6). The respective percent reabsorptions were 70+/-3 and 73+/-3% (p +/- 0.3). In order to determine whether the technique per se was suitable to detect changes in reabsorption, the proximal MIJ study was repeated by using the carbonic anhydrase inhibitor dichlorphenamide 3 x 10(-5) mol/l in the microinjectate: while SNGFR remained unchanged, percent reabsorption fell from 63+/-5 to 45+/-7% during injection of the diuretic, p < 0.03. We conclude that the technique is adequate to examine the effects of drugs, and that F does not reduce proximal volume absorption at concentrations of 3 x 10(-5) mol/l. The loop diuretic decreases distal volume absorption by abolishing the osmotic gradient between blood and tubular fluid along the early distal convoluted tubule.

Animals↗

PubMed1993

Effect of thiazide diuretics against neurally mediated contraction of guinea pig airways. Contribution of carbonic anhydrase.

The effect of thiazide diuretics on neurally and agonist-induced contractile responses of guinea pig airways in vitro were investigated. Tracheal or bronchial strips were suspended in organ baths and isometric tension recorded. Chlorothiazide (CTZ, 10(-4) to 3 x 10(-3) M), hydrochlorothiazide (HCTZ, 10(-3) M), and dichlorphenamide (DCPM, 10(-3) M) significantly potentiated contraction of tracheal strips induced by electrical field stimulation (EFS). They also increased acetylcholine (ACh)- but not carbachol-induced tracheal contraction. In the presence of atropine and propranolol, on the other hand, CTZ and DCPM but not HCTZ significantly inhibited EFS-induced contraction in bronchial strips. We determined whether carbonic anhydrase inhibition could mimic the effects of CTZ and DCPM. Acetazolamide (ATZ), an inhibitor of carbonic anhydrase, had no effect on either EFS- or ACh-induced contraction in tracheal strips but significantly inhibited nonadrenergic, noncholinergic (NANC) contractile responses induced by EFS in bronchial strips. CTZ, DCPM, and ATZ did not affect substance P-induced contractile responses in the bronchi. We conclude that CTZ, DCPM, and ATZ attenuate NANC neurally mediated bronchial contraction by preventing the release of contractile neuropeptides from sensory nerve endings. This effect may occur through inhibition of carbonic anhydrase activity. In addition, thiazide diuretics potentiate contractile responses to ACh in the trachea, probably through inhibition of acetylcholinesterase activity.

Acetylcholine↗

PubMed1977

[Increase in the oxygen available to the cerebral cortex after the administration of carbonic anhydrase inhibitors].

Oxygen tension (pO2) in cerebral cortex was measured by polarographic method in unanesthetized rabbits. Intravenous administration (25 mg/kg) of carbonic anhydrase inhibitors (acetazolamide, methazolamide, dichlorphenamide, sulthiame) induced an early important rise of cortical p O2, which is not dependent on increase of p O2 and p CO2 and decrease of pH in arterial blood. High dosage of acetazolamide (250 mg/kg) produced the same effect and did not suppress the increase of cortical p O2 under air-CO2 inhalation. This result suggests that CO2 might act specifically upon cerebral vessels.

Animals↗

PubMedDate not supplied

[Diuretic therapy in heart failure].

Diuretic therapy is a drug therapy that increases urine volume, but not glomerular filtration rate (GFR). The diuretics act predominantly on tubular sites; the drugs that increase GRF are the aminophyllines, the positive inotropy or vasoactive substances that increase afferent arteriolar flux or intraglomerular pressure. We can divide the diuretics into six categories: 1) carbonic anhydrase inhibitors: acetazolamide, dichlorphenamide, methazolamide; 2) osmotic diuretics: glycerol, mannitol, urea; 3) loop diuretics: furosemide, bumetanide, ethacrynic acid, piretanide, torsemide; 4) thiazide and thiazide-like diuretics: chlorothiazide, trichlormethiazide, indapamide, chlorthalidone, metolazone; 5) potassium-sparers: a) kidney epithelial sodium channel inhibitors: amiloride and triamterene; b) aldosterone receptor antagonists: spironolactone, canrenoate potassium, eplerenone; 6) ADH antagonists: lithium salts, demeclocycline and ethanol. Diuretic therapy is useful in treating acute and chronic renal insufficiency, congestive heart failure, cirrhosis, overhydration and hypertension. Diuretic therapy increases urine volume, ion loss (except Na+, K+), and modifies diffusion (dilute urine) and convection mechanisms (reduced tubular absorption). Therefore, diuretics are very useful non-dangerous drugs.

Diuretics↗

PubMed1985

On the pharmacology of L-645,151: a topically effective ocular hypotensive carbonic anhydrase inhibitor.

L-645,151 [(2-sulfamoyl-6-benzothiazolyl)-2,2-dimethylpropionate] is the O-pivaloyl ester of L-643,799 (6-hydroxybenzothiazole-2-sulfonamide), topically administered L-645,151 being a substrate for ocular esterases with the resultant liberation of the active moiety, L-643,799, during penetration of the ocular surface. The minimum concentrations of topically administered suspensions (1 drop of 50 microliters into both eyes) of L-645,151, L-643,799, dichlorphenamide and methazolamide significantly lowering the elevated intraocular pressure (IOP) of the alpha-chymotrypsinized rabbit eye were 0.25, 2, 10 and 5%, respectively. IOP was not significantly decreased by 10% suspensions of acetazolamide or ethoxzolamide. The IOP lowering action of L-645,151 was local as the unilateral instillation of L-645,151 (0.25%) into the contralateral eye was devoid of effect in alpha-chymotrypsinized rabbits. L-645,151 (2%) decreased aqueous humor inflow in both the conscious rabbit and the anesthetized dog. Outflow facility in the conscious rabbit was unaltered by a 10% suspension of L-645,151. Low peak levels (0.52 microgram/g) of L-643,799 were present in rabbit renal cortex after the instillation of L-645,151 (2%) into both eyes; this treatment did not induce diuresis in the conscious rabbit. The corresponding maximum concentration in the iris + ciliary body was 4.01 micrograms/g. These preclinical studies reveal that L-645,151 is the most potent, topically effective ocular hypotensive carbonic anhydrase inhibitor described to date.

Administration, Topical↗

PubMed1994

Comparison of postoperative phacoemulsification results in dogs with and without diabetes mellitus: 153 cases (1991-1992).

Data were collected from the medical records of 123 nondiabetic dogs (182 eyes) and 30 diabetic dogs (57 eyes) in which phacoemulsification surgery was performed. Pre- and postoperative comparisons, including signalment, initial ophthalmic examination findings, surgical variables, and postoperative findings for the short-term follow-up period (mean, 5.75 weeks), between nondiabetic and diabetic dogs revealed that the complication rate was not greater in the diabetic group. Postoperative uveitis was evident with nearly equal frequency (in nondiabetic dogs, 90% or 164 of 182 eyes and in diabetic dogs, 88% or 50 of 57 eyes). In nondiabetic dogs, 1% prednisolone ophthalmic solution and prednisone were administered pre- and postoperatively, and amoxicillin and dichlorphenamide postoperatively. In diabetic dogs, the same treatment regimen, except for treatment with flunixin meglumine IV at surgery and substitution of aspirin for prednisone, was used. When nondiabetic and diabetic dogs were treated according to their respective pre- and postoperative medical regimens, clinical differences in postoperative findings were not apparent.

Adrenal Cortex Hormones↗

PubMed1965