Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0432222 (SEM)
 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The activities of three enzymes--two mitochondrial and one microsomal--were measured in isolated islets of Langerhans from 2-month-old and 12-month-old rats. Mitochondrial glycerophosphate dehydrogenase activity (expressed as nanomoles of iodonitrotetrazolium reduced per minute per milligram of protein), decreased (P less than 0.01) from a mean (+/- SEM) of 73.2 +/- 11.2 (2-month-old) to 34.7 +/- 5.9 (12-month-old). In contrast, activities of neither mitochondrial monoamine oxidase nor microsomal NADH cytochrome-c reductase changed with age. These results demonstrate that the activity of the glycerophosphate shuttle decreases as rats grow older, and it raises the possibility that the consequent difficulty in regenerating cytosolic NAD+ may play a role in the insulin secretory defect associated with aging.
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PMID:Evidence of an age-related decline in mitochondrial glycerophosphate dehydrogenase activity of isolated rat islets. 635 35

The luteinizing hormone releasing hormone analog D-Trp6-Pro9-Net-LHRH (LHRHa) inhibits rat testicular testosterone secretion. To determine whether LHRHa decreases serum testosterone concentrations solely by inhibiting gonadotropin secretion or, in addition, by influencing directly testicular testosterone biosynthesis, we examined the effects of LHRHa on the activities of 5 key testicular steroidogenic enzymes. Thirty hypophysectomized, hOG treated rats were given either LHRHa (1 micrograms sc/day) or saline during 7 days. The LHRHa treated animals exhibited a significant decrease of serum testosterone when compared to the control group (498 +/- 37 ng/dl vs 2044 +/- 105 ng/dl, mean +/- SEM, P less than 0.001). 17-Hydroxyprogesterone serum levels were also decreased in the LHRHa treated rats (61 +/- 6 ng/dl vs 93 +/- 7 ng/dl, P less than 0.005), while serum progesterone levels were similar in both groups of animals. These changes in steroid concentrations were associated with decreases in the microsomal enzyme activities of 17-hydroxylase (37 +/- 9 vs 654 +/- 41 pmol/mg protein/min, P less than 0.001), 17,20-desmolase (103 +/- 9 vs 522 +/- 47 pmol/mg protein/min, P less than 0.001), 3 beta-hydroxysteroid dehydrogenase (1.7 +/- 0.02 vs 4.1 +/- 0.1 nmol/mg protein/min, P less than 0.001), aromatase (95 +/- 7 vs 228 +/- 6 pmol/mg protein/min, P less than 0.001) and 17-ketosteroid reductase (167 +/- 9 vs 290 +/- 18 pmol/mg protein/min, P less than 0.01) in the LHRHa treated animals. These findings indicate that LHRHa can inhibit directly rat testicular testosterone biosynthesis.
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PMID:Direct effect of the luteinizing hormone releasing hormone analog D-Trp6-Pro9-Net-LHRH on rat testicular steroidogenesis. 639 51

Epoxide formation from drugs, chemicals, food additives and environmental pollutants is catalyzed by cytochrome P-450 dependent monooxygenase(s). Epoxides are converted to glycols or dihydrodiols by epoxide hydrolase (EH). These enzymes are known to be present in the microsomes of different mammalian tissues and in the hepatic nuclei from rats and humans. The balance between the epoxide forming (AHH) and metabolizing (EH) enzyme activities may provide information about the "epoxide exposure" of a tissue. We thus investigated AHH and EH in the nuclear and microsomal fractions from six livers, four kidneys, four lungs, and two adrenals from human fetuses (gestational age between 15 and 24 weeks). Tissues were obtained at legal abortion for sociomedical reasons. AHH activity was measured according to van Cantfort et al (Biochem Biophys Res Commun 79: 505, 1977) using beno (a)pyrene as substrate. EH was measured as described by Jerina et al (Mol Pharmacol 13:342, 1977) using both styrene oxide (SO) and benzo(a)pyrene-4,5-oxide (BPO) as substrate. The nuclear fraction was isolated by a multistep procedure including centrifugation in high density sucrose ( Pacifici et al, unpublished). The hepatic AHH activity (pmole/min/mg; mean +/- SEM) was 11.5 +/- 2.2 in the nuclear fraction and 34.7 +/- 1.7 in the microsomes. In adrenals it was 6.0 (nuclei) and 4.4 (microsomes). The nuclear fraction from kidneys and lungs did not catalyze this reaction at a measurable rate, whereas microsomal AHH activity was 1.3 +/- 0.3 and 5.3 +/- 1.1, respectively, in these tissues.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Epoxide hydrolase and aryl hydrocarbon hydroxylase in human fetal tissues: activities in nuclear and microsomal fractions and in isolated hepatocytes. 667 72

To study further the role of hepatic cholesterol synthesis in patients with gallstones, the activity of the rate-limiting step in cholesterogenesis, hydroxymethyl glutaryl co-enzyme A reductase (HMGCoAR), was measured in operative wedge liver biopsies from ten patients with untreated cholesterol gallstones, six with pigment stones and ten controls. Hepatic HMGCoAR was also measured in six patients with cholesterol-rich gallstones treated for 1-24 months with 14.6-18.6 mg chenodeoxycholic acid (CDCA) kg-1 day-1, in two patients with radiolucent pigment stones treated with 17.3 and 17.7 mg CDCA kg-1 day-1 and in ten other patients with cholesterol-rich stones given 4.5-7.2 mg ursodeoxycholic acid kg-1 day-1 for 1-6 months. HMGCoAR activity was also related to the free and esterified cholesterol content of both hepatic homogenates and the microsomal fractions. Compared with the controls (HMGCoAR activity 14.6 +/- 1.6 (SEM) pmole mg microsomal protein-1 min-1), the mean activity in untreated cholesterol cholelithiasis was 32.2 +/- 2.0 (P < 0.001), but was near normal in patients with pigment stones (16.2 +/- 1.5). In cholesterol gallstone patients, chenodeoxycholic acid treatment reduced the mean enzyme activity by 51% compared with the untreated gallstone group (P < 0.001) and in smaller doses, ursodeoxycholic acid therapy lowered it by 40% (P < 0.001) but in the two patients with pigment stones, CDCA did not seem to affect HMGCoAR activity. Despite this four-fold variation in enzyme activity, there were no significant differences in mean free or esterified cholesterol concentrations in whole liver homogenates or in the microsomal fraction from any of the patient groups.
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PMID:Hepatic HMGCoA reductase in human cholelithiasis: effects of chenodeoxycholic and ursodeoxycholic acids. 677 60

Bilirubin diglucuronide (BDG) may be formed in vitro by microsomal UDP glucuronosyl transferase (EC 2.4.1.17)-mediated transfer of a second mole of glucuronic acid from UDP-glucuronic acid, or by dismutation of bilirubin monoglucuronide (BMG) to BDG and unconjugated bilirubin, catalyzed by an enzyme (EC 2.4.1.95) that is concentrated in plasma membrane-enriched fractions of rat liver. To evaluate the role of these two enzymatic mechanisms in vivo, [(3)H]bilirubin mono-[(14)C]glucuronide was biosynthesized, purified by thin-layer chromatography, and tracer doses were infused intravenously in homozygous Gunn (UDP glucuronyl transferase-deficient) rats or Wistar rats. Bilirubin conjugates in bile were separated by high-pressure liquid chromatography and (3)H and (14)C were quantitated. In Gunn rats, the (14)C:(3)H ratio in BDG excreted in bile was twice the ratio in injected BMG. In Wistar rats the (14)C:(3)H ratio in biliary BDG was 1.25 +/- 0.06 (mean +/- SEM) times the ratio in injected BMG. When double labeled BMG was injected in Wistar rats after injection of excess unlabeled unconjugated bilirubin (1.7 mumol), the (14)C:(3)H ratio in BDG excreted in bile was identical to the ratio in injected BMG. Analysis of isomeric composition of bilirubin conjugates after alkaline hydrolysis or alkaline methanolysis indicated that the bile pigments retained the IX(alpha) configuration during these experiments. The results indicate that both enzymatic dismutation and UDP glucuronyl transferase function in vivo in BDG formation, and that dismutation is inhibited by a high intrahepatic concentration of unconjugated bilirubin. This hypothesis was supported by infusion of [(3)H]bilirubin-monoglucuronide in isolated perfused homozygous Gunn rat liver after depletion of intrahepatic bilirubin by perfusion with bovine serum albumin (2.5%), and after bilirubin repletion following perfusion with 0.34 mM bilirubin. From 20 to 25% of injected radioactivity was recovered in BDG in bile in the bilirubin-depleted state; only 8-10% of radioactivity was in BDG in bile after bilirubin repletion. After infusion of [(3)H]bilirubin di-[(14)C]glucuronide in homozygous Gunn rats, 5-7% of the injected pigment was excreted in bile as BMG. The (14)C:(3)H ratio in the injected BDG was 10% greater than the (14)C:(3)H ratio in BMG excreted in bile. These results indicate that in vivo, dismutation rather than partial hydrolysis, is responsible for BMG formation. Incubation of [(3)H]bilirubin, BDG and a rat liver plasma membrane preparation resulted in formation of BMG (3.3 nmol/min per mg protein) indicating that dismutation is also reversible in vitro.
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PMID:Bilirubin diglucuronide formation in intact rats and in isolated Gunn rat liver. 680 Oct 91

The present study was undertaken to characterize the effects of ursodeoxycholic acid on biliary lipid metabolism in man. Fifteen gallstone patients were treated with ursodeoxycholic acid at a daily dosage of 15 mg per kg body weight for about 4 weeks before cholecystectomy. At operation a liver biopsy, together with gallbladder and hepatic bile, were obtained. Eighteen untreated gallstone patients undergoing cholecystectomy served as controls. During treatment with ursodeoxycholic acid, hepatic bile became unsaturated with cholesterol in all patients investigated. The total biliary lipid concentration remained unchanged. The hepatic cholesterol concentration decreased by about 20%. No significant change in the microsomal HMG CoA reductase activity was observed (38.5 +/- 6.7 pmol . min-1 . mg protein-1 vs 38.3 +/- 4.7 pmol . min-1 . mg protein-1 in the controls; means +/- SEM). Plasma concentrations of total cholesterol were reduced by about 10%, and those of high density lipoprotein (HDL) and low density lipoprotein (LDL) cholesterol by about 15%. Plasma triglyceride levels remained essentially unchanged during treatment. We conclude that, similar to chenodeoxycholic acid therapy, ursodeoxycholic acid treatment results in unsaturation of fasting hepatic bile. In contrast to the changes seen during chenodeoxycholic acid feeding, however, the unsaturation of hepatic bile during ursodeoxycholic acid treatment is not primarily related to a decreased hepatic HMG CoA reductase activity. Furthermore, while chenodeoxycholic acid tends to increase plasma LDL levels, such changes are not seen during ursodeoxycholic acid treatment.
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PMID:Ursodeoxycholic acid treatment in cholesterol gallstone disease: effects on hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase activity, biliary lipid composition, and plasma lipid levels. 685 53

It has been established that progesterone will induce 17 beta-estradiol (E2) dehydrogenase in the human endometrium. Whether it plays a similar role in the induction of estrogen sulfotransferase is not known, although this is likely, since estrone sulfate is the main metabolite of E2 when incubated with secretory, but not proliferative, human endometrium. We have now examined the influence of progesterone on both enzymes in endometrial tissue in organ culture. Estrogen sulfotransferase activity was not detectable in the cytosol of proliferative tissue when cultured in the absence of hormone, but was induced by culture in the presence of progesterone to a value (mean +/- SEM) of 19.7 +/- 5.3 pmol E2-3-sulfate h-1 mg cytosol protein-1. A significant (P less than 0.05) induction of E2 dehydrogenase activity was also observed in the same tissues [from 3.7 +/- 1.9 to 10.4 +/- 2.7 (mean +/- SEM) nmol estrone h-1 mg microsomal protein-1]. Corresponding values for secretory endometrium, when cultured under identical conditions in the absence of progesterone, were 20.3 +/- 11.6 pmole h-1 mg-1 and 31.1 +/- 25.1 nmol h-1 mg-1 for estrogen sulfotransferase and E2 dehydrogenase, respectively. Values not significantly different from these were obtained when progesterone was present in the cultures. These data indicate that progesterone secretion during the luteal phase is responsible for the induction of both E2 dehydrogenase and sulfotransferase activities in the endometrium. It is likely that these enzymes are closely coupled, resulting in the rapid metabolism of E2 by formation and excretion of estrone sulfate.
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PMID:Induction of estrogen sulfotransferase in the human endometrium by progesterone in organ culture. 695 31

The induced activity of aryl hydrocarbon hydroxylase (AHH), measured by the metabolism of benzo[a]pyrene to fluorescent products in cultured human lymphocytes, shows a strong seasonal variation. The in vivo metabolism of antipyrine, which is also catalyzed by microsomal cytochrome P-450-dependent monooxygenases, has been reported to be correlated with AHH inducibility in human lymphocytes. To determine whether antipyrine metabolism also showed seasonal changes, we measured antipyrine half-life (t 1/2) in 10 nonsmokers and eight smokers at the two times of the year that correspond to the high and low peaks of inducible AHH activity as measured in lymphocytes. The mean antipyrine t 1/2 determined in all 18 subjects in summer was almost identical to that found in winter (mean +/- SEM = 10.90 +/- 0.65 and 10.96 +/- 0.78 hr). AHH activity in cultured human lymphocytes from the nonsmoking subjects was determined in control and 3-methylcholanthrene-induced cells to obtained inducibility ratios of 4.2 +/- 0.56 (SEM) in the summer and 1.4 +/- 0.14 (SEM) in winter. These results indicate that the seasonal variation in AHH inducibility in human lymphocytes is not reflected by a corresponding seasonal variation in antipyrine metabolism in vivo.
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PMID:Absence of seasonal variation in antipyrine metabolism. 705 21

High-affinity binding of melatonin to crude membrane preparations of bovine pineal gland was examined by a rapid filtration procedure through Whatman GFB paper. Maximal melatonin binding was attained in 60 min at 37 degrees C, in 2 h at 25 degrees C and in 5 h at 0 degree C; at 25 and 37 degrees C it was 36 and 42% of that at 0 degree C. Specific binding was thermolabile and decreased following incubation with trypsin; it was also pH dependent, the maximum being observed at physiological pH. Melatonin binding was inhibited by the addition of monovalent or divalent ions to the incubation buffer. Subcellular fractionation studies indicated that 39 and 50% of binding was located in the pellets at 900 and 27,000 g whereas 11% was detected in the microsomal pellet. Scatchard analysis revealed a single population of binding sites with Kd = (7.0 +/- 1.5) 10(-7) M (mean +/- SEM, n = 4); binding site concentration ranged from 185 to 356 fmol/mg of protein. When various melatonin analogues were tested for their ability to inhibit (3H)-melatonin binding, the following Ki values (10(-7) M), were obtained: N-acetyl-serotonin 120, serotonin 130, 2-methyl indole 154, 5-hydroxytryptophol 218, 5-methoxytryptamine 266, 5-methoxytryptophol 660, tryptamine 1,740, 5-hydroxyindole acetic acid 3,455, 5-methoxyindole acetic acid 12,690, 5-hydroxytryptophan 13,600, and 6-hydroxymelatonin 55,550. Those results suggest that melatonin receptors may be present in the pineal gland.
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PMID:Binding sites for melatonin in bovine pineal gland. 722 76

This paper describes seven patients with radiolucent gallstones in functioning gallbladders who did not respond to chenodeoxycholic acid (CDCA). Despite large doses (greater than or equal to 19 mg CDCA/kg/day), CDCA-rich bile (CDCA conjugates 70-97% of total biliary bile acids) and greater than or equal to one year's treatment, their fasting duodenal bile remained supersaturated with cholesterol and their gallstones did not dissolve. Five patients came to cholecystectomy, gallstone analysis and liver biopsy for measurement of hepatic cholesterogenesis (HMGCoAR activity). In three who stopped CDCA before surgery, the mean HMGCoAR (pmol/mg microsomal protein/min) of 50.2 was higher than in our untreated gallstone controls (32.2 +/- SEM 2.0; P less than 0.05). Two patients who took CDCA until surgery had a mean HMGCoAR of 33.5--more than twice that in CDCA-treated gallstone controls. These findings suggest that non-response to CDCA may be related to high or unsuppressed hepatic cholesterogenesis. In one patient who did not respond to CDCA, treatment with 19 mg ursodeoxycholic acid/kg/day did desaturate his bile.
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PMID:Lack of response to chenodeoxycholic acid in obese and non-obese patients. Role of cholesterol synthesis and possible response to ursodeoxycholic acid. 746 67


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