thiourea and acetamide

As an extension of our analysis of the effect of halogenation on thiourea TRPV1 agonists, we have now modified selected 4-hydroxy(or 4-amino)-3-methoxyphenyl acetamide TRPV1 agonists by 5- or 6-halogenation on the aromatic A-region and evaluated them for potency for TRPV1 binding and regulation and for their pattern of agonism/antagonism (efficacy). Halogenation shifted the functional activity at TRPV1 toward antagonism with a greater extent of antagonism as the size of the halogen increased (I>Br>Cl), as previously observed for the thiourea series. The extent of antagonism was greater for halogenation at the 5-position than at the 6-position, in contrast to SAR for the thiourea series. In this series, compounds 55 and 75 showed the most potent antagonism, with K(i) (ant)=2.77 and 2.19nM, respectively, on rTRPV1 expressed in Chinese hamster ovary cells. The compounds were thus ca. 40-60-fold more potent than 6'-iodononivamide.

Topics: Acetamides; Animals; Benzamides; Capsaicin; CHO Cells; Cricetinae; Cricetulus; Halogenation; Rats; Structure-Activity Relationship; Thiourea; TRPV Cation Channels

Gulf toadfish (Opsanus beta) use a unique pulsatile urea excretion mechanism that allows urea to be voided in large pulses via the periodic insertion or activation of a branchial urea transporter. The precise cellular and subcellular location of the facilitated diffusion mechanism(s) remains unclear. An in vitro basolateral membrane vesicle (BLMV) preparation was used to test the hypothesis that urea movement across the gill basolateral membrane occurs through a cortisol-sensitive carrier-mediated mechanism. Toadfish BLMVs demonstrated two components of urea uptake: a linear element at high external urea concentrations, and a phloretin-sensitive saturable constituent (K(m) = 0.24 mmol/l; V(max) = 6.95 micromol x mg protein(-1) x h(-1)) at low urea concentrations (<1 mmol/l). BLMV urea transport in toadfish was unaffected by in vitro treatment with ouabain, N-ethylmaleimide, or the absence of sodium, conditions that are known to inhibit sodium-coupled and proton-coupled urea transport in vertebrates. Transport kinetics were temperature sensitive with a Q(10) > 2, further suggestive of carrier-mediated processes. Our data provide evidence that a basolateral urea facilitated transporter accelerates the movement of urea between the plasma and gills to enable the pulsatile excretion of urea. Furthermore, in vivo infusion of cortisol caused a significant 4.3-fold reduction in BLMV urea transport capacity in lab-crowded fish, suggesting that cortisol inhibits the recruitment of urea transporters to the basolateral membrane, which may ultimately affect the size of the urea pulse event in gulf toadfish.

Topics: 4-Chloromercuribenzenesulfonate; Acetamides; Animals; Batrachoidiformes; Biological Transport; Cell Membrane; Crowding; Epithelial Cells; Gills; Hydrocortisone; Kinetics; Methylurea Compounds; Phloretin; Sodium-Potassium-Exchanging ATPase; Temperature; Thiourea; Urea

The possible presence of a urea transporter in the kidney of the gulf toadfish (Opsanus beta) and further characterization of the pulsatile facilitated transporter previously identified in its gills were investigated by comparing the extra-renal and renal handling of two urea analogues with the handling of urea. Toadfish were fitted with caudal artery and indwelling urinary ureteral catheters and injected with an iso-osmotic dose of (14)C-labelled urea analogue (acetamide or thiourea) calculated to bring plasma analogue concentrations close to plasma urea concentrations. Branchial permeabilities to urea, acetamide and thiourea were similar during non-pulsing periods and all increased during pulse events, although urea permeability was greater than analogue permeability during pulses. The incidence and magnitude of acetamide and urea pulses at the gills were significantly correlated, acetamide pulses being 35-50 % of the size of urea pulses. However, the thiourea and urea pulses at the gills were only weakly correlated, thiourea pulses being less than 16 % of the size of urea pulses. Thiourea inhibited branchial urea excretion by reducing the pulse frequency. The renal handling of thiourea and urea were similar in that both substances were more concentrated in the urine than in the plasma, whereas acetamide was found in equal concentrations in the urine and plasma. Urea and thiourea were secreted 2-3 times more effectively than Cl(-) and water, whereas acetamide was secreted at a similar relative rate. The differential handling of the urea analogues by the gills and kidney indicates the presence of a different, possibly unique, transporter in the kidney. The movement of thiourea and urea into the renal tubule against an apparent concentration gradient suggests the presence of an active transport mechanism.

Topics: Acetamides; Animals; Biological Transport, Active; Branchial Region; Carrier Proteins; Fishes; Kidney; Membrane Glycoproteins; Membrane Transport Proteins; Thiourea; Urea; Urea Transporters

We tested the hypothesis that urea transport in rainbow trout (Oncorhynchus mykiss) embryos is dependent, in part, on a bidirectional urea-transport protein. Acute exposure to phloretin and urea analogs [acetamide, thiourea, 1,(4-nitrophenyl)-2-thiourea] reversibly inhibited urea excretion from the embryos to the external water. Unidirectional urea influx was inhibited by acetamide and thiourea, with IC(50) values of 0.04 and 0.05 mmol l(-1), respectively. Influx of urea from the external water to the embryo tended to saturate at elevated external urea concentrations (V(max)=10.50 nmol g(-1) h(-1); K(m)=2 mmol l(-1)). At very high urea concentrations (20 mmol l(-1)), however, a second, non-saturable component was apparent. These results indicate that urea excretion in trout embryos is dependent, in part, on a phloretin-sensitive facilitated urea transporter similar to that reported in mammalian inner medullary collecting ducts and elasmobranch kidney.

Topics: Acetamides; Animals; Biological Transport; Oncorhynchus mykiss; Phloretin; Thiourea; Urea

The thick ascending limb of Henle's loop (TALH) is thought to be involved in the regulation of the renal urea gradient.. We have characterized the uptake of urea (oil density centrifugation and 2-compartment-culture) and volume regulation (impedance measurement) in highly differentiated cells derived from rabbit outer medulla.. TALH cells exposed to 600 mOsm/liter (300 mM urea) shrunk to 72 +/- 5% of the isoosmotic volume. Due to a regulatory volume increase (RVI), the cell volume was almost completely regained at 92 +/- 6% after five minutes. The uptake of 14C-urea in the presence of urea concentrations up to 600 mM did not show any saturation. In the presence of phloretin the urea uptake decreased to 69 +/- 14%. The transport was sodium and chloride independent. Changing the membrane potential caused an increase of regulatory volume increase and urea uptake. Hyperosmolarity induced by sucrose (300 mM) and NaCl (150 mM) caused a decrease of urea uptake to 70 +/- 14% and 53 +/- 11%, respectively. The permeability coefficient (P) in a two compartment culture was P = 1.7 . 10(-6) +/- 0.39.10(-6) cm/second, suggesting a relatively low permeability.. Due to the low permeability, it seems impossible to achieve a physiologically significant participation of the TALH in the urea circulation within the nephron. However, the results of this study provides significant hints about the existence of a specific urea transport mechanism that enables the cell to adapt rapidly to different osmolarities.

Topics: Acetamides; Animals; Biological Transport; Cell Line; Cell Polarity; Diffusion Chambers, Culture; Ionophores; Kidney Medulla; Loop of Henle; Methylurea Compounds; Osmolar Concentration; Potassium Chloride; Rabbits; Thiourea; Urea; Valinomycin

To provide further background data on the wing spot somatic mutation and recombination assay, 10 selected carcinogens (acetamide, acrylamide, benzo(a)pyrene, cyclophosphamide, diethylstilbestrol, 4-nitroquinoline N-oxide, propyleneimine, safrole, thiourea, and o-toluidine) were tested in this assay. 72-h-old third-instar larvae, trans-heterozygous for 2 recessive wing cell markers: multiple wing hairs (mwh) and flare3 (flr3) were fed with 3 concentrations of each carcinogen during the rest of their development until pupation, and the genotoxic effects were measured as significant increases in the appearance of visible mutant hair clones on the adult wing blade. Our results show that 6 of the carcinogens tested produce significant increases in wing spot frequency, at least at one of the concentrations assayed. Benzo(a)pyrene, diethylstilbestrol, safrole and thiourea were the compounds that did not increase the incidence of mutant clones.

Topics: 4-Nitroquinoline-1-oxide; Acetamides; Acrylamide; Acrylamides; Animals; Aziridines; Benzo(a)pyrene; Biological Assay; Carcinogens; Cyclophosphamide; Diethylstilbestrol; Drosophila melanogaster; Mutagenicity Tests; Safrole; Thiourea; Toluidines; Wings, Animal

Acetohydroxamic acid (AHA), a urea analogue, is used clinically to dissolve struvite stones because it inhibits the urease produced by Proteus mirabilis. To be effective, the concentration of AHA must be high in the collecting duct system and final urine. Because AHA is structurally similar to urea, we investigated whether AHA is transported by the urea carrier found in the terminal inner medullary collecting duct (IMCD) and the erythrocyte. We examined AHA transport under four conditions known to affect urea movement across the terminal IMCD, i.e., stimulation by vasopressin (AVP) and hyperosmolality, and inhibition by phloretin and urea analogues. The AHA permeability was determined with a 10 mM bath-to-lumen AHA gradient. AHA was measured by ultramicrocolorimetry. Addition of 1 nM AVP to the bath increased the AHA permeability of the perfused terminal IMCD. Increasing perfusate and bath osmolality from 290 to 690 mosmol/kgH2O (by adding NaCl) also increased tubule permeability to AHA. Addition of either 0.25 mM phloretin to the bath or 200 mM thiourea to the lumen reversibly inhibited the AVP-stimulated AHA permeability. AHA-induced osmotic lysis of erythrocytes was inhibited by phloretin or thionicotinamide; AHA inhibited the osmotic lysis induced by the urea analogue acetamide. Thus, in the rat terminal IMCD, both urea and AHA transport are stimulated by AVP and hyperosmolality, and both are inhibited by phloretin and thiourea. In erythrocytes, both urea and AHA transport are inhibited by phloretin or thionicotinamide. Thus AHA is transported by the urea carrier in the terminal IMCD and erythrocyte.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Acetamides; Animals; Arginine Vasopressin; Biological Transport; Erythrocytes; Hydroxamic Acids; In Vitro Techniques; Kidney Medulla; Kidney Tubules, Collecting; Osmolar Concentration; Permeability; Phloretin; Rats; Rats, Sprague-Dawley; Thiourea; Urea; Urease

To increase the number of chemicals tested using the zeste-white (UZ) somatic mutation assay, ten selected carcinogens (acetamide, acrylamide, benzo(alpha)pyrene, cyclophosphamide, diethylstilbestrol, 4-nitroquinoline N-oxide, propyleneimine, safrole, thiourea, and o-toluidine) have been evaluated in this assay. Our results show that all the compounds tested produce significant increases in the eye spot frequency at, at least, one of the concentrations assayed, indicating that the zeste-white assay appears to be highly sensitive to these carcinogenic compounds. That is in agreement with data previously reported by other authors.

Topics: 4-Nitroquinoline-1-oxide; Acetamides; Acrylamide; Acrylamides; Animals; Aziridines; Benzo(a)pyrene; Carcinogens; Cyclophosphamide; Diethylstilbestrol; Drosophila melanogaster; Mutagenicity Tests; Mutagens; Safrole; Thiourea; Toluidines

Radiation inactivation was used to determine the nature and molecular weight of water and urea transport pathways in brush border membrane vesicles (BBMV) isolated from rabbit renal cortex. BBMV were frozen to -50 degrees C, irradiated with 1.5 MeV electrons, thawed, and assayed for transport or enzyme activity. The freezing process had no effect on enzyme or transport kinetics. BBMV alkaline phosphatase activity gave linear ln(activity) vs. radiation dose plots with a target size of 68 +/- 3 kDa, similar to previously reported values. Water and solute transport were measured using the stopped-flow light-scattering technique. The rates of acetamide and osmotic water transport did not depend on radiation dose (0-7 Mrad), suggesting that transport of these substances does not require a protein carrier. In contrast, urea and thiourea transport gave linear ln(activity) vs. dose curves with a target size of 125-150 kDa; 400 mM urea inhibited thiourea flux by -50% at 0 and 4.7 Mrad, showing that radiation does not affect inhibitor binding to surviving transporters. These studies suggest that BBMV urea transport requires a membrane protein, whereas osmotic water transport does not.

Topics: Acetamides; Animals; Biological Transport, Active; Body Water; Kidney Cortex; Kinetics; Mathematics; Microvilli; Molecular Weight; Osmosis; Permeability; Rabbits; Thiourea; Urea

Acetamide and N-methylurea have been shown for the first time to be substrates for jack bean urease. In the enzymatic hydrolysis of urea, formamide, acetamide, and N-methylurea at pH 7.0 and 38 degrees C, kcat has the values 5870, 85, 0.55, and 0.075 s-1, respectively. The urease-catalyzed hydrolysis of all these substrates involves the active-site nickel ion(s). Enzymatic hydrolysis of the following compounds could not be detected: phenyl formate, p-nitroformanilide, trifluoroacetamide, p-nitrophenyl carbamate, thiourea, and O-methylisouronium ion. In the enzymatic hydrolysis of urea, the pH dependence of kcat between pH 3.4 and 7.8 indicates that at least two prototropic forms are active. Enzymatic hydrolysis of urea in the presence of methanol gave no detectable methyl carbamate. A mechanism of action for urease is proposed which involves initially an O-bonded complex between urea and an active-site Ni2+ ion and subsequently an O-bonded carbamato-enzyme intermediate.

Topics: Acetamides; Benzoates; Benzoic Acid; Carbamates; Fluoroacetates; Formamides; Hydrogen-Ion Concentration; Kinetics; Methylurea Compounds; Models, Chemical; Nitrobenzenes; Phenylcarbamates; Structure-Activity Relationship; Substrate Specificity; Thiourea; Trifluoroacetic Acid; Urea; Urease

The exposure of erythrocytes from the elasmobranch, Squalus acanthias, to solutions isosmotic with plasma (IM) but containing urea or hydroxyurea as the sole solute does not produce hemolysis. Exposure of these cells to IM methylurea, thiourea and acetamide does produce hemolysis. Low concentrations of urea, which are associated with hemolysis, protect dogfish red cells against hemolysis by methylurea and thiourea. Dogfish red cells exposed to mediums containing high concentrations of urea, or no urea, reach 95 percent of their equilibrium concentration in less than 5 minutes.

Topics: Acetamides; Amides; Animals; Biological Transport; Dogfish; Erythrocytes; Facilitated Diffusion; Hemolysis; Metabolism; Methylurea Compounds; Pharmacology; Research; Sharks; Thiourea; Urea

The renal tubules of the shark actively reabsorb urea. They also can reabsorb acetamide and methylurea, but there is no evidence for active reabsorption of thiourea. The specificity of the transport system thus appears to be different from the urea secretory system in the frog in which thiourea is secreted but acetamide and methylurea are not secreted.

Topics: Acetamides; Amides; Animals; Biological Transport; Elasmobranchii; Kidney Tubules; Metabolism; Methylurea Compounds; Physiology; Research; Sharks; Thiourea; Urea

Topics: Acetamides; Acetates; Dental Pulp Cavity; Dentin; Humans; Niacin; Niacinamide; Thiourea; Time and Motion Studies; Tooth; Urea

Topics: Acetamides; Acetates; Autoradiography; Dental Enamel; Humans; Niacin; Niacinamide; Thiourea; Time and Motion Studies; Tooth; Urea