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Biomedical subjects

R Showalter

Publications and source records attributed to R Showalter.

13 recordsLinked to original sources
PubMed2001

Orlistat maintains biliary lipid composition and hepatobiliary function in obese subjects undergoing moderate weight loss.

OBJECTIVES: Orlistat, an intestinal lipase inhibitor, has recently been approved by the US Food and Drug Administration for treatment of obesity. The effects of orlistat on hepatobiliary function have not been previously defined. A 4 wk study was performed involving modest weight loss in obese subjects to observe any short-term hepatobiliary responses that occur after initiating treatment with orlistat and a hypocaloric diet. METHODS: A total of 23 obese (BMI 30-41 kg/m2) subjects were randomized to a double blind t.i.d. treatment with 120 mg of orlistat or a placebo in conjunction with a hypocaloric diet (1200-1500 kcal/day). The study was designed to achieve similar modest weight loss in both groups in order to be able to directly assess the effects of orlistat. Cholesterol saturation, bile composition, and gallbladder motility were measured. RESULTS: At the end of the treatment period, mean weight loss of 3.8 kg was achieved in the orlistat group (vs 2.3 kg with placebo, p = NS). Total bile acid concentration decreased significantly with placebo (-18.57 +/- 6.99 mmol/L; 95% CI = -32.26 to -4.87), but not with orlistat. Biliary phospholipid concentration decreased significantly with placebo (-4.38 +/- 1.91 mmol/L; 95% CI = -8.13 to -0.64) but not with orlistat. Mean changes from the baseline in cholesterol saturation index and gallbladder motility were similar in both groups. Microscopy of bile failed to reveal cholesterol microcrystals before or after treatment in either group. CONCLUSIONS: Our findings indicate a primary initial effect of weight loss is a reduction in biliary bile acids and phospholipids. Orlistat blocks these adverse changes in biliary lipid composition and maintains hepatobiliary function. We speculate that the risk of formation of gallstones during weight loss may actually be lowered with orlistat.

Adult↗
PubMed1998

Two-site interaction of nuclear factor of activated T cells with activated calcineurin.

Transcription factors belonging to the nuclear factor of activated T cells (NFAT) family regulate the expression of cytokine genes and other inducible genes during the immune response. The functions of NFAT proteins are directly controlled by the calcium- and calmodulin-dependent phosphatase calcineurin. Here we show that the binding of calcineurin to NFAT is substantially increased when calcineurin is activated with calmodulin and calcium. FK506.FKBP12 drug-immunophilin complexes inhibited the interaction of NFAT with activated calcineurin much more effectively than they inhibited the interaction with inactive calcineurin, suggesting that part of the interaction with activated calcineurin involved the enzyme active site. We have previously shown that NFAT is targeted to inactive calcineurin at a region distinct from the calcineurin active site (Aramburu, J., Garcia-Cozar, F. J., Raghavan, A., Okamura, H., Rao, A., and Hogan, P. G. (1998) Mol. Cell 1, 627-637); this region is also involved in NFAT binding to activated calcineurin, since binding is inhibited by an NFAT peptide spanning the calcineurin docking site on NFAT. The interacting surfaces are located on the catalytic domain of the calcineurin A chain and on an 86-amino acid fragment of the NFAT regulatory domain. NFAT binding to the calcineurin catalytic domain was inhibited by the calcineurin autoinhibitory domain and the RII substrate peptide, which bind in the calcineurin active site, as well as by the NFAT docking site peptide, which binds to a region of calcineurin distinct from the active site. We propose that, in resting cells, NFAT is targeted to a region of the calcineurin catalytic domain that does not overlap the calcineurin active site. Upon cell activation, displacement of the autoinhibitory domain by calmodulin binding allows NFAT to bind additionally to the calcineurin active site, thus positioning NFAT for immediate dephosphorylation at functional phosphoserine residues.

Amino Acid Sequence↗
PubMed1997

Postmenopausal estrogen therapy selectively stimulates hepatic enlargement in women with autosomal dominant polycystic kidney disease.

The goal of this study was to determine whether use of postmenopausal estrogen (Premarin, Wyeth-Ayerst, Philadelphia, PA) in women with autosomal dominant polycystic kidney disease (ADPKD) increases liver, hepatic cyst, or kidney volume. We also determined whether clinical symptoms correlated with the volume of either the liver or kidneys. Eight women off estrogen (control, C) and 11 others on estrogen (Premarin, E) were studied basally and after 1 year. The two groups were similar in age, weight, age at menarche, and gravida. Volumes of total liver, hepatic cysts, hepatic parenchyma, and total kidney were measured by a validated computed tomography (CT) technique. Estrogen treatment was associated with a selective increase in total liver volume (E vs. C: delta = 7% +/- 12% vs. -2% +/- 8%, P < .03) and no change in kidney volume (E vs. C: delta = 0% +/- 6% vs. -2% +/- 6%, P = NS). Symptoms were common, regardless of estrogen treatment (abdominal pain 60%, shortness of breath 40%, or both 35%). Patients with symptoms of abdominal pain and shortness of breath had significantly increased hepatic volumes (P < .03) but similar kidney volume compared with patients without symptoms. We conclude that estrogen treatment of postmenopausal ADPKD women is associated with selective liver enlargement and that abdominal symptoms in ADPKD patients may be because of extensive hepatic cystic disease.

Antipyrine↗
PubMed1997

Quantitative liver function tests define the functional severity of liver disease in early-stage cirrhosis.

Some patients with early-stage cirrhosis preserve hepatic function, whereas others have little hepatic reserve and rapidly deteriorate. The aim of this study was to use quantitative tests of liver function (QLFTs) to define the degree of functional hepatic impairment in patients with early-stage cirrhosis (Child-Pugh score 5-7) and to determine whether the tests predicted subsequent hepatic decompensation. We recruited 10 cirrhotic (Cr) patients and 10 healthy controls (NI), who were well matched for race, age, weight, and gender. Clearances of caffeine (CF) and antipyrine (AP) after oral administration were measured from timed samples of saliva. The clearance of cholate (CA) was measured from serum samples obtained after simultaneous oral ([2,2,4,4-2H]CA) and intravenous ([24-13C]CA) administration. CA shunt was calculated as (Cl i.v./Clo x 100%). CF elimination rate (Cr v NI, mean +/- SD: 0.03 +/- 0.02 v 0.075 +/- 0.018 h-1, P < .0005) and AP clearance (24 +/- 16 v 40 +/- 7 mL/minute, P < .02) were reduced in Cr patients. CA shunt was increased in Cr patients (43 +/- 18 v 18 +/- 7%, P < .002). Five Cr patients decompensated during follow-up and had the worst CA shunts (76%, 66%, 51%, 48%, and 45%). Three subsequently received successful orthotopic liver transplantation, 1 died of hepatoma, and 1 is on the waiting list for transplantation. In conclusion, QLFTs define the degree of functional impairment in early cirrhosis and may identify Cr patients at greatest risk of decompensation who may require transplantation for survival.

Administration, Oral↗
PubMed1991

Genetic analysis in vibrio.

Bacteria of the genus Vibrio are remarkably diverse, and until recently the methodology for genetic analysis consisted of a patchwork of different approaches, many of which were narrowly applicable to a single species. The invention of the recombinant DNA technology and the subsequent innovations in transposon mutagenesis and in transductive and conjugative gene transfer techniques have led to the development of very powerful and general strategies for genetic analysis of species of Vibrio. The striking synergy of combining recombinant DNA, transposon, and gene transfer methods is particularly evident in the construction of transposons which generate gene fusions and of broad host range plasmids which deliver transposons and mutated genes and which mobilize chromosomes. With such tools it should be possible to perform advanced genetic analysis on the many undomesticated species of Vibrio still to be explored.

Cloning, Molecular↗
PubMed1989

Identification of a locus controlling expression of luminescence genes in Vibrio harveyi.

Mutagenesis with transposon mini-Mulac was used to identify loci containing genes for bioluminescence (lux) in the marine bacterium Vibrio harveyi. Transposon insertions which resulted in a Lux- phenotype were mapped to two unlinked regions of the genome. Region I contained the luxCDABE operon which was previously shown to encode the enzymes luciferase and fatty acid reductase, which are required for light production. The other locus, region II, which was identified for the first time in this study, appeared to have a regulatory function. In Northern blot analysis of mRNA from mutants with defects in this region, no transcription from the luxCDABE operon could be detected. Strains with transposon-generated lux::lacZ gene fusions were used to analyze control of the transcription of these regions. Expression of luminescence in the wild type was strongly influenced by the density of the culture, and in strains with the lacZ indicator gene coupled to the luxCDABE operon, beta-galactosidase synthesis was density dependent. So, transcription of this operon is responsive to a density-sensing mechanism. However, beta-galactosidase synthesis in strains with lacZ fused to the region II transcriptional unit did not respond to cell density. The organization and regulation of the lux genes of V. harveyi are discussed, particularly with regard to the contrasts observed with the lux system of the fish light-organ symbiont Vibrio fischeri.

Blotting, Southern↗
PubMed1983

Gallbladder and small intestinal regulation of biliary lipid secretion during intraduodenal infusion of standard stimuli.

The gallbladder and small intestine are reservoirs for the bile acid pool during its enterohepatic circulation and, as such, may regulate biliary secretion of bile acid. During studies of biliary bile acid secretion, a stimulus to gallbladder contraction is continuously infused into the duodenum. Under these conditions, it is assumed that the gallbladder is tonically contracted and that the rate of bile acid secretion into the duodenum equals the hepatic bile acid secretion rate. However, secretion rates vary by as much as 100%, depending upon which of two standard stimuli is used. Therefore, we studied the role of gallbladder emptying and small intestinal transit in determining biliary lipid secretion rate and composition during infusion of these stimuli in five healthy subjects. Each subject was studied with a liquid formula containing 40% of calories as fat, and with an amino acid solution for 10 h. Bile acid, phospholipid, cholesterol, and markers were measured in duodenal bile and hourly secretion rates were calculated by marker dilution technique. Real-time gallbladder sonographs and serum pancreatic polypeptide levels were obtained every 30 min. Small bowel transit time was estimated levels were obtained every 30 min. Small bowel transit time was estimated by the breath hydrogen response after giving lactulose intraduodenally.During liquid formula infusion, gallbladder emptying was more complete, small intestinal transit was faster, and pancreatic polypeptide levels were higher. Secretion rates of all lipids were greater and molar percent cholesterol was lower. For the combined data from both infusions, the secretory relationships of cholesterol to bile acid, cholesterol to phospholipid, and phospholipid to bile acid were curvilinear. We conclude that more complete gallbladder emptying and faster intestinal transit increase the enterohepatic cycling of bile acids and lower the molar percent cholesterol of bile. Some of the fluctuation observed in biliary lipid secretion rates, especially during amino acid infusion, is due to gallbladder refilling and emptying.

Adult↗
PubMed1982

Biliary lipids, bile acids, and gallbladder function in the human female: effects of contraceptive steroids.

Individuals who take contraceptive steroids or estrogens are at increased risk of developing cholesterol gallstones. The mechanisms of the increased stone formation are incompletely understood. In this study we report biliary lipid composition and secretion, bile acid composition and kinetics, and gallbladder function in a group of healthy, nonobese women taking a contraceptive steroid preparation. A comparable group of healthy women served as controls. Bile-rich duodenal fluid was obtained after stimulation of gallbladder contraction; bile acid, phospholipid, and cholesterol concentrations were determined. Biliary lipid secretion rate was measured by the marker perfusion technique. Bile acid distribution was determined by gas-liquid chromatography. The pool size, FTR, and synthesis rate of each bile acid were measured by using CA and CDCA labeled with the stable isotope of carbon, 13C. In some of the subjects gallbladder storage and emptying were measured during the kinetic study, by real-time ultrasonography. Contraceptive steroid use was associated with a significant increase in biliary cholesterol saturation and in the lithogenic index of bile. The rate of cholesterol secretion in the contraceptive steroid group was 50% greater than in the control (p much less than 0.001) and the rate of bile acid secretion was reduced (p less than 0.02). The total bile acid pool size was significantly increased by contraceptive steroids. The major increase occurred in the CA pool (p less than 0.04). The daily rate of enterohepatic cycles of the bile acid pool was decreased by contraceptive steroids from 6.6 to 4.3 (p less than 0.01). The only effect of contraceptive steroids on gallbladder function was a slower emptying rate in response to intraduodenal amino acid infusion. No index of gallbladder function correlated significantly with any parameter of bile acid kinetics in this small group of subjects. The findings confirm the lithogenic effect of contraceptive steroids and indicate that its causes are an increase in cholesterol secretion and a decrease in bile acid secretion.

Bile↗
PubMed1981

Biliary lipids, bile acids, and gallbladder function in the human female. Effects of pregnancy and the ovulatory cycle.

To study the events that might lead to an increased risk of cholesterol gallstones, we examined biliary lipid composition and secretion and bile acid composition and kinetics at different stages of pregnancy or ovulation in young, nonobese, healthy women. Lipid composition and bile acid distribution were determined in duodenal fluid obtained in the fasting state and after stimulation of the gallbladder. Biliary lipid secretion was measured by the marker-perfusion technique. Bile acid kinetics were determined with cholic and chenodeoxycholic acids labeled with carbon13, by measuring the relative abundance of 13C in duodenal bile acids for 4--5 d. In a subset of patients we measured gallbladder storage and emptying during the kinetic study. The phase of the ovulatory cycle had no effects, but there were significant changes during pregnancy. The lithogenic or cholesterol saturation index of fasting hepatic and gallbladder bile increased during the second and third trimesters. The mean secretion rate of biliary lipids was not altered, but in the last two-thirds of pregnancy, cholesterol secretion increased in relation to bile acid and phospholipid secretion. There was a progressive decrease in the percentage of chenodeoxycholic acid and a similar increase in the percentage of cholic acid. The pool size of each major bile acid increased in the first trimester. Chenodeoxycholic acid and deoxycholic acid pools, but not cholic acid pools, subsequently decreased. The fractional turnover rate of both primary bile acids was slower during pregnancy. The synthesis rate of chenodeoxycholic but not cholic acid decreased in a linear manner during the first 20 wk of pregnancy. The rate of enterohepatic cycling of the bile acid pool was reduced throughout pregnancy. The volume of the fasting gallbladder and the residual volume after a physiologically stimulated contraction were directly correlated with bile acid pool size. The residual volume was also directly related to total bile acid synthesis.

Adult↗
PubMed1978

Reversal by triton WR-1339 of ethynyloestradiol-induced hepatic cholesterol esterification.

RATS TREATED WITH ETHYNYLOESTRADIOL HAVE MARKED HYPOLIPIDAEMIA: serum cholesterol is decreased to 5%, triacylglycerol to 10% and phospholipid to 70% of control concentrations. Loss of serum cholesterol follows an exponential decay, with a half-life of 1.13+/-0.09 days. After 4 days of treatment, serum cholesterol concentrations remain relatively constant (ranging from 1 to 20mg/100ml) for at least 30 days. There is a concomitant 20-fold decrease in the d<1.21 fraction of serum proteins and a similar decrease in serum apolipoproteins as measured by sodium dodecyl sulphate/10%-polyacrylamide-gel electrophoresis. The activity of hepatic microsomal acyl-CoA-cholesterol O-acetyltransferase (EC 2.3.1.26) was significantly increased by ethynyloestradiol treatment (P<0.05). This activation caused hepatic cholesteryl esters containing mainly C(18:1) fatty acids to increase linearly as serum cholesterol concentrations decreased (r=0.9675, P<0.001). Triton WR-1339, a non-ionic detergent that inhibits lipoprotein catabolism, was used to estimate hepatic lipid secretion by measuring the increment in serum lipids after its administration. At 15h after Triton WR-1339 administration, serum cholesterol concentrations were increased equally in both control and ethynyloestradiol-treated rats. In contrast, the increment of serum triacylglycerol of treated rats was 40% of that found in control rats, indicating that ethynyloestradiol inhibits hepatic triacylglycerol secretion. Triton WR-1339 inhibited the oestrogen activation of hepatic microsomal acyl-CoA-cholesterol O-acyltransferase and restored hepatic cholesteryl ester concentrations to normal values. These data suggest that ethynyloestradiol and its pharmacological ;antagonist' Triton WR-1339 alter hepatic triacylglycerol secretion via a mechanism associated with changes in hepatic cholesterol esterification.

Animals↗
PubMed1978

Alterations of hepatic Na+,K+-atpase and bile flow by estrogen: effects on liver surface membrane lipid structure and function.

Administration of the synthetic estrogen ethinyl estradiol (17alpha-ethinyl-1,3,5-estratriene-3,17beta-diol) decreases hepatic Na(+),K(+)-ATPase (ATP phosphohydrolase; EC 3.6.1.3) activity and bile flow to 50% and alters the composition and structure of surface membrane lipid in rats. Although the content of phospholipids was not changed by treatment, free cholesterol (130%) and cholesterol esters (400%) were increased in liver surface membrane fractions. These observations correlate with changes in membrane viscosity, as shown by electron spin resonance probes. Both rotational correlation time, using the isotropic probe methyl (12-nitroxyl)stearate, and the order parameter, determined by the anisotropic probe 5-nitroxylstearic acid, were significantly increased in liver surface membrane fractions from rats treated with ethinyl estradiol. Administration of Triton WR-1339, a nonionic detergent that corrects hepatic and serum lipid changes caused by ethinyl estradiol treatment, restored toward normal elevated membrane lipids and viscosity as well as Na(+),K(+)-ATPase activity and bile flow. Although restoration of normal liver surface membrane structure and function may be due to reversal of abnormal lipid composition, detergents also may directly alter membrane enzyme activity. Addition of Triton WR-1339 in vitro increased Na(+),K(+)-ATPase activity and reduced membrane viscosity of surface membranes from rats treated with ethinyl estradiol. Triton had no effect on either parameter in normal membrane preparations. Studies of membrane structure and function both in vivo and in vitro suggest that alterations in lipid composition may alter Na(+),K(+)-ATPase function and bile flow.

Animals↗
PubMed1975

In vivo effect of bile salts and cholestyramine on intestinal anaerobic bacteria.

In vitro studies have shown that some bile salts inhibit the growth of intestinal bacteria. We investigated the possibility that bile salts might have a similar action in vivo in the ileum by performing serial anaerobic cultures and bile salt analyses on postprandial ileal fluid obtained anaerobically via intestinal tube. Five subjects were studied under control conditions, and after a 1-week course of orally administered cojugated bile salts in a dose shown to increase the bile salt pool. Three of the subjects were also studied after a 1-week course of cholestyramine. The numebr of ileal anaerobic microorganisms decreased significantly after both bile salt and cholestyramine treatment. Ileal bile salt concentrations were generally high (mean 9.2 mM) and did not change significantly after either bile salt or cholestyramine treatment. The results of this study are unexplained. Although it is possible that bile salts play a role in the regulation of small intestinal anaerobic flora, the lack of a relationship between ileal bile salt concentration and population levels of anaerobic organisms is puzzling and raises further questions about such a role for bile salts.

Adult↗