Synthesis Rates

The rate of cholate synthesis in man is about 200-300 mg/day, as measured by isotope dilution studies. The chenodeoxycholate synthesis rate is similar, so that the total primary bile salt synthesis is about 400-600 mg daily for a healthy adult, and when in the steady state this amount is also the daily fecal excretion rate (12). 

Values for turnover time, pool size, and half-life of cholate and chenodeoxycholate and the excretion rates for both are given in Table I. When turnover time or synthesis rates are calculated from isotope dilution studies, the values are usually in the same range as those derived from isotope balance studies provided that the latter are done by properly validated and reproducible methods. 

Maximum synthesis rates in man can be induced by complete interruption of the enterohepatic circulation so that no bile salts are returned to the liver to suppress synthesis. Surgical construction of a total external bile 

TABLE I. Values for Bile Salt Turnover, Half-life, and Pool Size in Man 

Subjects and conditions (No. subjects) Total formation or excretion (mg/day) Cholate Chenodeoxycholate  

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Example 3 Phosgene Synthesis Rate data were obtained by Potter... 

Transcriptional regulation encompasses the modulation of the synthesis rate of mRNA due to cell type specific factors that may be triggered by external stimuli. 

Figure 9.33. Ammonia synthesis rate and current response to a step change in the catalyst potential Uwr of the promoted Fe/CaZro9lno, Oj.u catalyst,43 Reprinted with permission from the American Chemical Society.

Figure 8.9. Methanol synthesis rate over a Cu(lOO) single crystal in a 1 1 gas mixture of H2 and CO2 at ptot =...

These effects profoundly influence the ammonia, as shown in Fig. 8.28 where the ammonia synthesis rate is plotted for two basal planes of iron and the same iron surfaces modified with 0.1 Ml of potassium. 

The turnover rate of a transmitter can be calculated from measurement of either the rate at which it is synthesised or the rate at which it is lost from the endogenous store. Transmitter synthesis can be monitored by administering [ H]- or [ " C]-labelled precursors in vivo these are eventually taken up by neurons and converted into radiolabelled product (the transmitter). The rate of accumulation of the radiolabelled transmitter can be used to estimate its synthesis rate. Obviously, the choice of precursor is determined by the rate-limiting step in the synthetic pathway for instance, when measuring catecholamine turnover, tyrosine must be used instead of /-DOPA which bypasses the rate-limiting enzyme, tyrosine hydroxylase. 

Trulson, ME., and Ulissey. J.J. Chronic cocaine administration decreases dopamine synthesis rate and increases [ H] spiroperidol binding in rat brain. Brain Res Bull 19 35-38, 1987. 

Hofffnan DJ, Niyogi SK. 1977. Metal mutagens and carcinogens affect RNA synthesis rates in a distinct manner. Science 198 513-514. 

Fig. 6 A, B. Time profiles of P(3HB) synthesis rate of A recombinant B wild type R. eutropha during the batch culture in a minimal medium containing 20 g/1 of glucose (reproduced from [78] with permission)... 

Protein and RNA synthesis rates were significantly stimulated in liver, and inhibited in muscle in a dose-dependent manner. Maximum effect in both tissues occurred at 5 mg/L for protein synthesis and 0.2 mg/L for RNA synthesis... 

Iglesia8 (and references therein) reviewed early work on supported Co catalysts, mostly focused on titania as the support. In general, indigenous or added water initially (at low levels) increase the synthesis rates on a 12.1% Co/Ti02 catalyst. However, at higher water concentrations the effect is saturated, and the rates are much more weakly affected by further increases in the water concentration. 

The inactivation must be placed in context with the steady-state enzyme synthesis rate, which can be simply described ... 

Aldous CN, Chetty CS, Mehendale HM, et al. 1984. Lack of effects of chlordecone on synthesis rates, steady-state levels and metabolises of catecholainines in rat brain. Neurotoxicology 5(2) 59-65. 

Fischer-Tropsch synthesis rates, metal crystallite size and support effects, 39 242-246... 

The level of DOPA accumulation (decreased by agonists and increased by antagonists) in different brain parts after the administration of dopaminergic test compounds can be taken as an indirect measure of the DA synthesis rate. Such a biochemical test model can be used in normal animals and in reserpine or GBL pretreated animals (see below). 

R.A. Varin, T. Czujko, E.B. Wasmund, Z. Wronski, Catalytic effects of various forms of nickel on the synthesis rate and hydrogen desorption properties of nanocrystalhne magnesium hydride (MgH ) synthesized by controUed reactive mechanical milhng (CRMM), J. Alloys Compd. 432 (2007) 217-231. 

ASBT has a complex regulatory system reflecting the importance of this transporter to bile-acid pool size and bile-acid synthesis rates. Hepatic nuclear factor la (HNF-la) is necessary for expression of ASBT as knockout mice showed no expression and had defective bile-acid transport.Conversely, FXR-null mice showed no difference in expression of ASBT, showing that FXR plays no part in regulation of ASBT. In man, HNF-la controls baseline promoter activity of the ASBT gene as the minimal construct with full promoter activity was found to have 3 HNF-la binding sites. These authors also showed that the promoter construct bound peroxisome proliferator activated receptor a (PPARa)/9 cis retinoic acid receptor heterodimer, demonstrating a link between bile-acid absorption and hepatic lipid metabolism mediated by PPARa. 

The liver meets the larger part (60%) of its requirement for cholesterol by de novo synthesis from acetylcoen-zyme-A. Synthesis rate is regulated at the step leading from hydroxymethyl-glutaryl CoA (HMG CoA) to mevalonic acid (p. 157A), with HMG CoA reductase as the rate-limiting enzyme. 

However, studies in hypercholesterolemic subjects, using soy protein depleted of isoflavones have shown that soy protein independently of isoflavones can favorably affect LDL size, LDL particle distribution was shifted to a less atherogenic pattern,and can decrease triglyceride concentrations, triglyceride fatty acid fractional synthesis rate, and cholesterol... 

Wang Y, Jones PJ, Ausman LM, Lichtenstein AH. Soy protein reduces triglyceride levels and triglyceride fatty acid fractional synthesis rate in hypercholesterolemic subjects. Atherosclerosis 173, 269-275, 2004. 

Ho AKS, Loh HH, Craves F, et al The effect of prolonged lithium treatment on the synthesis rate and turnover of monoamines in brain regions of rats. Fur J Pharmacol 10 72-78, 1970... 

The NH3 synthesis rate is proportional to 0 . Since the calculated synthesis rate is in reasonable agreement with independent measurements, it is unlikely that the low value of 0 should be significantly in error. 

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