Biomedical subjects

R Lester

Publications and source records attributed to R Lester.

At least 37 records · Page 2Linked to original sources

PubMed1988

Bile salt-induced calcium fluxes in artificial phospholipid vesicles.

The ionic permeability of selected biological membranes is increased by bile salts. To examine changes in calcium permeability during the exposure of artificial membranes to bile salts, we investigated calcium uptake by unilamellar and multilamellar phospholipid vesicles. In the presence of 750 microM taurodeoxycholate, uptake of radiolabelled calcium by unilamellar vesicles increased 2.5-fold over control values. Calcium uptake by multilamellar vesicles as measured with a free calcium indicator, arsenazo III, increased 2.2- or 21-fold in the presence of 60 microM lithocholate or 3 beta-hydroxy-5-cholenoate, respectively. Results were directly influenced by experimental variables such as bile salt hydrophobicity, external calcium concentration, and the bile salt/lipid molar ratio. Observed membrane solubilization was minimal despite increased calcium permeability. Comparison of radiolabelled calcium uptake with radiolabelled sodium or radiolabelled rubidium uptake indicated that bile salt-dependent calcium uptake was 60-140-times greater than bile salt-dependent uptake of either monovalent cation. In an effort to delineate forces affecting calcium translocation, vesicles were exposed either to valinomycin, which induced an electrochemical gradient across the membrane, or to nigericin, which induced a proton gradient. Exposure to valinomycin minimally influenced bile salt-induced calcium uptake while exposure to nigericin significantly promoted uptake by 40-70%. The results suggest that bile salts promote calcium uptake by a mechanism which may be similar to those of other carboxylic ionophores.

Arsenazo III↗

PubMed1988

Efficacy of esmolol in the treatment and transfer of patients with supraventricular tachyarrhythmias to alternate oral antiarrhythmic agents.

The efficacy and safety of esmolol, a titratable intravenous beta-adrenergic blocking agent with a short elimination half-life (t 1/2 = 9.0 min) was evaluated in a multicenter open-label study for the treatment of supraventricular tachyarrhythmias (heart rate greater than 100 bpm). The study also investigated the feasibility of transferring patients from esmolol to alternate oral antiarrhythmic agents without loss of therapeutic response. Of the 113 patients studied, 95 (84%) achieved therapeutic response (reduction in heart rate of 15% or more or conversion to sinus rhythm). Most of these patients (93%) achieved the therapeutic response at esmolol doses of 200 micrograms/kg/min or lower. Transfer from esmolol to an oral antiarrhythmic agent(s) was studied in 76 patients. Alternate antiarrhythmic agents used in this study were digoxin (N = 25), propranolol (N = 21), verapamil (N = 10), metoprolol (N = 11), quinidine (N = 2), and a combination of two antiarrhythmic agents (N = 7). Sixty-seven (88%) patients were successfully transferred to oral antiarrhythmic agents without loss of the therapeutic response obtained with esmolol. The most frequent adverse effect observed during the study was hypotension, which resolved quickly (16 +/- 14 min) either by decreasing the dose or by discontinuation of esmolol infusion. This study supports previous observations concerning the safety and efficacy of esmolol in the treatment of supraventricular tachyarrhythmias. Furthermore, it demonstrates that the majority of patients successfully treated with esmolol can be safely and effectively transferred to oral therapy with alternate antiarrhythmic agents.

Adrenergic beta-Antagonists↗

PubMed1988

Bile acids increase cellular free calcium in cultured kidney cells (LLC-PK).

Suspensions of LLC-PK1 cells were used to determine the effect of bile acids on the cellular homeostasis of inorganic ions. It is determined that bile acids alter cellular free calcium (Cai) levels in LLC-PK1 cells. A series of bile acids were compared and found to produce increases in Cai in the order: lithocholate sulfate (LCS) greater than deoxycholate greater than chenodeoxycholate greater than lithocholate glucuronide greater than cholate. LCS (300 microM) produces changes in Cai (measured using Fura-2) qualitatively similar to those produced by 1 microM ionomycin, except that only ionomycin is able to release calcium from intracellular stores. The effect on Cai is roughly proportional to LCS concentration between 50 and 300 microM. The presence of 40 mM Na in the extracellular medium reduces the LCS-induced rise in Cai to 20% of that observed in the absence of Na. This effect is specific for Na versus 150 mM extracellular K, Li, or TMA. The effect is not dependent on the Na gradient across the membrane. At concentrations of LCS which induce changes in Cai, no significant effect of LCS is observed on either cellular Na or K levels, or intracellular pH.

Animals↗

PubMed1988

Intestinal absorption of bile acid glucuronides in rats.

While the intestinal absorption of taurine, glycine, and sulfate conjugates of bile acids has been studied extensively, nothing is known about the absorption of bile acid glucuronides. In the present study, the intestinal phase of the enterohepatic circulation of two bile acid glucuronides was examined. [3 beta-3H]cholic acid 3-O-beta-D-glucuronide or [3 beta-3H]lithocholic acid 3-O-beta-D-glucuronide was perfused through isolated segments of ileum or jejunum with intact blood supply in rats prepared with a biliary fistula. [14C]Taurocholic acid was perfused simultaneously with each glucuronide to compare glucuronide absorption with that of an actively transported bile acid. Intestinal absorption was determined by measuring the rate of secretion of labeled bile acid in bile. The absorption of [3H]cholic acid glucuronide by the ileum and jejunum was one fortieth and one eighth, respectively, that of [14C]taurocholic acid. Comparison of the two glucuronides show that [3H]lithocholic acid glucuronide absorption was 18 and 10 times greater than [3H]cholic acid glucuronide absorption from the jejunum and ileum, respectively. Collectively, the above observations suggest that glucuronidation of bile acids markedly reduces absorption from the small intestine.

Animals↗

PubMed1988

Biosynthesis of hydroxyl-linked glucuronides of short-chain bile acids by rat liver 3-hydroxysteroid UDP-glucuronosyltransferase.

Microsomal preparations from livers of Sprague-Dawley rats catalyze the glucuronidation of 3 alpha-hydroxy-5 beta-H (3 alpha, 5 beta) short-chain bile acids (C20-C23), predominantly at the hydroxyl group, while the glucuronidation of 3 beta, 5 beta short-chain bile acids occurs exclusively at the carboxyl group. A similar pattern of conjugation was also observed in Wistar rats having normal levels of 3-hydroxysteroid UDP-glucuronosyltransferase. Significant reductions of formation rates for hydroxyl-linked, but not carboxyl-linked, short-chain bile acid glucuronides were observed in hepatic microsomes from Wistar rats with low 3-hydroxysteroid UDP-glucuronosyltransferase activity. 3-Hydroxysteroid UDP-glucuronosyltransferase, purified to homogeneity from Sprague-Dawley liver microsomes, catalyzed the 3-O-glucuronidation of 3 alpha, 5 beta C20-23 bile acids, as well as of lithocholic and isolithocholic acids (C24). The apparent Michaelis constants (KM) for short-chain bile acids were similar to the value obtained for androsterone. 3 alpha, 5 beta-C20 and 3 beta, 5 beta-C20 competitively inhibited glucuronidation of androsterone by the purified 3-hydroxysteroid UDP-glucuronosyltransferase. Purified 17 beta-hydroxysteroid and p-nitrophenol UDP-glucuronosyltransferases did not catalyze the glucuronidation of bile acids. In addition, none of the purified transferases catalyzed the formation of carboxyl-linked bile acid glucuronides. The results show that 3-hydroxysteroid UDP-glucuronosyltransferase, an enzyme specific for 3-hydroxyl groups of androgenic steroids and some conventional bile acids, also catalyzes the glucuronidation of 3 alpha-hydroxyl (but not carboxyl) groups of 3 alpha, 5 beta short-chain bile acids.

Animals↗

PubMed1988

Calcium transport in plasma membrane subfractions of rat liver.

The selective demonstration of ATP dependent calcium uptake and calcium dependent phosphorylation of a 135 kD intermediate in isolated basolateral liver plasma membrane vesicles suggest that the basolateral plasma membrane of rat hepatocytes contains an ATP dependent calcium transport system with an apparent molecular weight of 135,000. The failure to demonstrate ATP dependent calcium uptake in simultaneously isolated canalicular plasma membrane vesicles suggests the absence of a similar ATP dependent calcium transport system on the canalicular domain. Additional phosphoproteins of 200 and 110 kD could be assigned to microsomal contamination of the isolated plasma membrane subfractions. A canalicular specific 70 kD phosphorylated intermediate presumably does not represent a Ca++ ATPase. Calcium dependent phosphorylation of the basolateral 135 kD intermediate is maximal at physiologic pH (7.0, 7.5), when the calcium pump is active but not at pH 8.0. The 135 kD phosphoprotein has also been shown for erythrocyte Ca++ ATPase and for kidney basolateral Ca++ ATPase (De Smedt et al., 1984; Niggli et al., 1979).

Adenosine Triphosphate↗

PubMed1988

Formation of three types of glucuronides of 6-hydroxy bile acids by rat liver microsomes.

The glucuronidation of 6-hydroxylated bile acids by rat liver microsomes was studied in vitro; for comparison, several major bile acids lacking a hydroxyl group in position 6 were also investigated. The highest reaction rates were found for lithocholic and deoxycholic acid (10.2 +/- 0.2 and 7.3 +/- 1.4 nmol/mg.min, respectively); our results for these substrates agree well with published values. Glucuronidation rates for the 6 beta-hydroxylated bile acids 3 alpha, 6 beta-dihydroxy-5 beta-cholanoate (murideoxycholate) and 3 alpha, 6 beta, 7 beta-trihydroxy-5 beta-cholanoate (beta-muricholate) were only slightly lower (3.7 +/- 0.3 and 3.6 +/- 0.3 nmol/mg.min). 6 alpha-Hydroxylated bile acids were glucuronidated at rates that were lower than those for their 6 beta-hydroxy counterparts. Rigorous product identification by high-field proton NMR of methyl/acetyl derivatives revealed that while bile acids lacking a 6-hydroxyl group gave rise exclusively to the typical 3-O-glucuronide, the presence of a hydroxyl group in position 6 led to the formation, in ratios depending on the substrate, of three types of conjugate: the 3-O-, the 6-O-, and the carboxyl-linked (acyl-) glucurnide. The latter is the first example of an acyl glucuronide of a bile acid of conventional (C24) size.

Animals↗

PubMed1987

Two laboratory methods for diagnosis of herpes simplex keratitis.

Two techniques are described which enable a rapid diagnosis of herpes simplex keratitis to be made. The tests, antibody/antigen reactions, were shown to be accurate and sensitive in the 119 patients examined. A result is available within four hours with the indirect peroxidase-antiperoxidase method and within one hour with the direct method. The techniques are relatively inexpensive, though labour intensive. Negative reactions were found in treated cases and in those with some delay in the histochemical staining.

3,3'-Diaminobenzidine↗

PubMed1987

Taurodeoxycholate and the developing rabbit distal colon: absence of secretory effect.

Failure to absorb bile acids by the ileum leads to fluid secretion by the colon and diarrhea in adults. The infant ileum, however, does not actively transport bile acids. Therefore, we investigated the effect of taurodeoxycholic acid (TDCA) on ion transport in the colon of rabbits 7-10 days old. We mounted distal colon from infant and adult rabbits in modified Ussing chambers and exposed the mucosal or serosal surfaces to TDCA. In the adult, 50 microM TDCA produced an increase in short-circuit current (delta Isc = 1.0 +/- 0.3 mu eq . h-1 . cm-2, P less than 0.05) and Cl secretion. In the infant, the effect was different, Isc was reduced (delta Isc = -1.1 +/- 0.2 mu eq . h-1 . cm-2, P less than 0.01) and ion flux was not altered. Microscopy demonstrated that the infant epithelium was not significantly damaged by exposure to TDCA at these concentrations. The infant colon was, however, capable of a secretory response to a variety of agonists including theophylline, carbachol, bradykinin, serotonin, and 12,13-dibutyryl phorbol ester. The infant rabbit distal colon lacks a secretory response to TDCA during that period when the ileum cannot transport bile acids.

Animals↗

PubMed1987

Glucuronidation of 6 alpha-hydroxy bile acids by human liver microsomes.

The glucuronidation of 6-hydroxylated bile acids by human liver microsomes has been studied in vitro; for comparison, several major bile acids lacking a 6-hydroxyl group were also investigated. Glucuronidation rates for 6 alpha-hydroxylated bile acids were 10-20 times higher than those of substrates lacking a hydroxyl group in position 6. The highest rates measured were for hyodeoxy- and hyocholic acids, and kinetic analyses were carried out using these substrates. Rigorous product identification by high-field proton nuclear magnetic resonance and by electron impact mass spectrometry of methyl ester/peracetate derivatives revealed that 6-O-beta-D-glucuronides were the exclusive products formed in these enzymatic reactions. These results, together with literature data, indicate that 6 alpha-hydroxylation followed by 6-O-glucuronidation constitutes an alternative route of excretion of toxic hydrophobic bile acids.

Adult↗

PubMed1987

Hyodeoxycholate-6-O-glucuronide cannot be quantitated with 3 alpha-hydroxysteroid dehydrogenase.

The reaction of the 6-hydroxylated bile acid, hyodeoxycholic acid, and its 6-O-glucuronide conjugate with 3 alpha-hydroxysteroid dehydrogenase was examined. A standard end-point assay and determination of the initial rates of reaction showed only minimal activity of the enzyme toward hyodeoxycholate-6-glucuronide in spite of the presence of a free 3 alpha-hydroxyl group. It was established that 6-hydroxylation itself did not significantly affect the enzyme reaction. It is concluded that the 6-glucuronide either blocks or hinders enzyme access to the 3-hydroxyl group.

3-Hydroxysteroid Dehydrogenases↗

PubMed1987

Vulpecholic acid (1 alpha, 3 alpha, 7 alpha-trihydroxy-5 beta-cholan-24-oic acid): a novel bile acid of a marsupial, Trichosurus vulpecula (Lesson).

A novel trihydroxylated C24 bile acid was isolated from the gallbladder bile of the Australian opossum, Trichosurus vulpecula (Lesson). This acid, for which the name vulpecholic acid is proposed, was identified as 1 alpha, 3 alpha, 7 alpha-trihydroxy-5 beta-cholan-24-oic. The structure proof included mass spectral and 1H and 13C nuclear magnetic resonance characterization of all crucial derivatives obtained by: oxidation of the methyl ester to a triketone with the enolizable 1,3-diketone function; methylation of this triketone to two isomeric methyl enol ethers; and reductive removal of oxygen functions from this triketone to give 5 beta-cholan-24-oic and 7-oxo-5 beta-cholan-24-oic acids. Vulpecholic acid was found in the bile in the unconjugated form; it accounted for more than 60% of the solid bile material. The marsupial T. vulpecula is the first example of a mammal secreting a 1 alpha-hydroxylated bile acid as well as the first example of a mammal secreting the major bile acid in a free form.

Animals↗

PubMed1986

Cellular mechanisms of cholestasis.

Concepts regarding the pathogenesis of cholestasis continue to evolve as investigational techniques improve and molecular mechanisms of bile formation are clarified. With the accumulation of information it is becoming increasingly evident that cholestasis results from not one but multiple disturbances in the sequence of events responsible for bile production. In addition to the inhibition of bile flow attributable to initiating events, cholestasis itself may inhibit bile flow by altering the intra- and extracellular environments of liver cells. Many questions about cholestasis remain unanswered, but future directions for research are suggested by the information currently available.

Actin Cytoskeleton↗

PubMed1986

Glucuronides of monohydroxylated bile acids: specificity of microsomal glucuronyltransferase for the glucuronidation site, C-3 configuration, and side chain length.

The ability of rat liver microsomes to catalyze UDP-glucuronic acid-dependent glucuronidation of monohydroxy-bile acids was examined. The following bile acids were used as substrates, each as the 3 alpha and 3 beta epimer: 3-hydroxy-5 beta-cholanoic acid (C24), 3-hydroxy-5 beta-norcholanoic acid (C23), 3-hydroxy-5 beta-bisnorcholanoic acid (C22), 3-hydroxy-5 beta-pregnan-21-oic acid (C21), and 3-hydroxy-5 beta-androstane-17 beta-carboxylic acid (C20). The corresponding glucuronides were chemically synthesized to serve as standards and were characterized by thin-layer and gas-liquid chromatography as well as by nuclear magnetic resonance. Enzymatic glucuronidation reactions were optimized with respect to pH for each product formed and the kinetic parameters for each reaction were measured. Analytical techniques necessary to separate products from unreacted substrates and to identify them included thin-layer chromatography, gas-liquid chromatography, and nuclear magnetic resonance. It was found that the 3 alpha epimers of the five bile acids listed above enzymatically formed 3-O-glucuronides, C24 being the best substrate, followed by C21 and C20; C22 and C23 gave rise to only small amounts of this product. The 3 beta epimers of all bile acids tested were poorer substrates, although by a factor that varied widely. In addition to the expected hydroxyl-linked glucuronide, three of the 3 alpha-bile acids (C23, C22, and C20) and at least one 3 beta-bile acid (C20), gave rise to a novel metabolite in which the 1-OH of glucuronic acid was esterified with the steroidal carboxyl group (carboxyl-linked glucuronide).

Animals↗

PubMed1986

Primary biliary cirrhosis.

Primary biliary cirrhosis often presents insidiously but progresses relentlessly in its later stages. Asymptomatic patients, however, may have a relatively benign course. Clinical, laboratory and histologic characteristics support an autoimmune pathogenesis. The complications of primary biliary cirrhosis are secondary to severe cholestasis, portal hypertension and progressive hepatocellular dysfunction. Currently, treatment is only supportive; no drug regimen has been shown to alter the disease course.

Adult↗

PubMed1986

[Epidemiology of human hydatidosis in the Province of Río Negro, Argentina].

The number of human cases with hydatidosis in the Province de Río Negro in the period 1969-1983 was determined by a retrospective exam of the registers at the Provincial Ministry of Health. From 1216 cases the yearly numbers between 59.4 in 1969-78 and 124.4 cases between 1979-83. This implies a yearly of 3.24 X 10,000 and with the most frequent localization in the liver. The average days of hospitalization was 29.2 per patient. The highest correspond to the southern departments of the Province 6.57 X 10,000 in the 40 Sanitary Zone. Eighty two and thirty five per cent of the cases had immunological confirmation with DD5, before surgery. The census allowed us to determine that rates of prevalence were in school children 1.09%, in conscripts, 0.28% and in adult settlers 2.58%. The average of positive serological cases in the province, was 0.77%. The yearly number of cases diagnoses is estimated in 4% of the existent carriers and is the highest in the world. The followup and control of children who had surgery, allowed us to detect that 30% of the cases presented new hydatid cyst before the 5 year lapse. Different factors put Río Negro with the highest rates of denounced human hydatidosis. These are related to living conditions around cattle farms and the socio economics and educational factors, which are analyzed in this paper. Modifications in the Programme for the control of hydatidosis has been put into action by the sanitary authorities.

Adult↗

PubMed1986

Preparation and characterization of 3-monohydroxylated bile acids of different side chain length and configuration at C-3. Novel approach to the synthesis of 24-norlithocholic acid.

A series of 3-monohydroxylated bile acids, in unlabeled and radioactive form, of varying side chain length and configuration at C-3 has been synthesized and rigorously characterized. They include: 3 alpha- and 3 beta-hydroxy-5 beta-androstane-17 beta-carboxylic acids (C20); 3 alpha- and 3 beta-hydroxy-5 beta-pregnan-21-oic acids (C21); 3 alpha- and 3 beta-hydroxy-23,24-bisnor-5 beta-cholan-22-oic acids (C22); 3 alpha- and 3 beta-hydroxy-24-nor-5 beta-cholan-23-oic acids (C23, norlithocholic and isonorlithocholic acids); and 3 beta-hydroxy-5 beta-cholan-24-oic acid (C24, isolithocholic acid). A novel approach to the degradation of lithocholic acid acetate to 24-norlithocholic acid is described. This degradation involves the photochemical modification of a Hunsdiecker reaction and Kornblum oxidation of the intermediate 23-bromide. The availability of these compounds makes it possible to study the metabolism and biological effects of short chain bile acids.

Bile Acids and Salts↗

PubMed1985

[An echographic, serologic and radiologic register of human hydatidosis. Contributions to a control program].

Between June and November 1984, 904 asymptomatic people from endemic areas of hydatidosis in Rio Negro, Argentina, were studied by means of ultrasonography (U.S.) and double diffusion for arc five (dd5). The population included 272 inhabitants from Pilcaniyeu, 55 patients from the Zonal Bariloche Hospital admitted for diseases other than hydatidosis and 577 recruits from different departments of the Rio Negro Province. A chest X-ray was performed in every recruits. 47 (5.20%) cases of hepatic hydatidosis were detected by U.S.; 11 (1.22%) were detected by dd5 (p 0.01); 2 (0.34%) were detected by chest X-ray. Due to the low sensitivity of dd5 a presumptive diagnosis of hydatidosis should be made in every patient proceeding from an endemic area with a liver cyst diagnosed by ultrasound, even if dd5 is negative. U.S. must be incorporated as an elective method associated with chest X-ray and dd5 in epidemiological yielding and monitoring of control programs for hydatidosis.

Adolescent↗