scholarly journals The effect of exogenous δ-aminolaevulinate on rat liver haem and cytochromes

1972 ◽  
Vol 129 (5) ◽  
pp. 1095-1099 ◽  
Author(s):  
Robert Druyan ◽  
Aldon Kelly
Keyword(s):  
Rat Liver ◽  
Synthetase Activity ◽  
Adult Rats ◽  
Adult Rat ◽  
Haem Biosynthesis ◽  
Rate Limiting ◽  
Mitochondrial Cytochromes ◽  
Hepatic Cytochrome

The activity of δ-aminolaevulinate synthetase is generally regarded as rate-limiting for hepatic haem biosynthesis. It has been suggested that cytochrome synthesis may also be regulated by changes in δ-aminolaevulinate synthetase activity. This hypothesis was studied by injecting product, δ-aminolaevulinate, into adult rats over a 4–240h period. The concentrations of hepatic mitochondrial cytochromes a, b, c and c1 were unchanged by treatment with δ-aminolaevulinate, allylisopropylacetamide or phenobarbital. In control animals, total microsomal haem content equalled the sum of cytochromes b5 plus P-450. After δ-aminolaevulinate administration the total amount of microsomal haem, measured as the pyridine haemochromogen, exceeded these components, indicating the formation of a ‘free’ haem pool. Haem synthesis does not appear rate-limiting for hepatic cytochrome synthesis in the adult rat.

scholarly journals A model for the regulation of δ-aminolaevulinate synthetase induction in rat liver

1973 ◽  
Vol 134 (4) ◽  
pp. 847-857 ◽  
Author(s):  
Govindarajan Padmanaban ◽  
Manchanahalli R. Satyanarayana Rao ◽  
Krishnamachari Malathi
Keyword(s):  
Rat Liver ◽  
Actinomycin D ◽  
Reciprocal Relationship ◽  
Synthetase Activity ◽  
Drug Resistant ◽  
Adult Rats ◽  
Adult Rat ◽  
Young Rats ◽  
Young Rat ◽  
Cytochrome P 450

A reciprocal relationship exists between the cytochrome P-450 content and δ-aminolaevulinate synthetase activity in adult rats. In young rats the basal δ-aminolaevulinate synthetase activity is higher and the cytochrome P-450 content is lower compared with the adult rat liver. Administration of allylisopropylacetamide neither induces the enzyme nor causes degradation of cytochrome P-450 in the young rat liver, unlike adult rat liver. Allylisopropylacetamide fails to induce δ-aminolaevulinate synthetase in adrenalectomized–ovariectomized animals or intact animals pretreated with successive doses of the drug, in the absence of cortisol. The cortisol-mediated induction of the enzyme is sensitive to actinomycin D. Allylisopropylacetamide administration degrades microsomal haem but not nuclear haem. Haem does not counteract the decrease in cytochrome P-450 content caused by allylisopropylacetamide administration, but there is evidence for the formation of drug-resistant protein-bound haem in liver microsomal material under these conditions. Phenobarbital induces δ-aminolaevulinate synthetase under conditions when there is no breakdown of cytochrome P-450. On the basis of these results and those already published, a model is proposed for the regulation of δ-aminolaevulinate synthetase induction in rat liver.

Postnatal expression of the canalicular bile acid transport system of rat liver

1991 ◽  
Vol 260 (5) ◽  
pp. G743-G751 ◽  
Author(s):  
D. A. Novak ◽  
C. J. Sippel ◽  
M. Ananthanarayanan ◽  
F. J. Suchy
Keyword(s):  
Bile Acid ◽  
Rat Liver ◽  
Initial Rate ◽  
Kinetic Studies ◽  
Precipitation Method ◽  
Disulfonic Acid ◽  
Acid Transport ◽  
Adult Rats ◽  
Bile Acid Transport ◽  
Adult Rat

Canalicular plasma membrane (CPM) vesicles prepared by a Ca2+ precipitation method from developing (7 and 14 days old) and adult rat liver were used to directly examine the postnatal ontogenesis of taurocholate (TC) transport. The initial rate of 50 microM TC uptake by vesicles derived from 14-day-old and adult but not 7-day-old animals was markedly inhibited by the anion transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). DIDS-sensitive TC uptake was 21.6 +/- 5.6 (SE) at 14 days compared with 58.1 +/- 8.1 pmol.mg protein-1.5 s-1 in adults (P less than or equal to 0.01). Kinetic studies were performed by preloading these predominantly "right-side out" vesicles with TC (25-800 microM) and measuring the initial rate (5 s) of efflux into bile salt-free medium. Computer analysis of the DIDS-sensitive portion of efflux revealed saturable kinetics with a similar Vmax (2.72 +/- 0.36 vs. 1.97 +/- 0.17 nmol.mg protein-1.min-1; P = NS) but a threefold higher Km (0.35 +/- 0.09 vs. 0.11 +/- 0.02 mM; P less than or equal to 0.05) in 14 day vs. adult CPM vesicles. In contrast, efflux from 7 day CPM vesicles increased linearly with increasing concentrations of TC and was not inhibited by DIDS. Immunoblots of canalicular membranes, probed with an antibody against the 100-kDa bile acid transport protein, showed that the amount of immunoreactive carrier protein in the membranes of 14-day-old and adult rats was similar but was only 37% of the adult level at 7 days of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of delta-aminolevulinic acid synthetase in muscle by exercise or thyroxine

1979 ◽  
Vol 236 (3) ◽  
pp. R180-R183 ◽  
Author(s):  
J. O. Holloszy ◽  
W. W. Winder
Keyword(s):  
Thyroid Hormones ◽  
Aminolevulinic Acid ◽  
Treadmill Running ◽  
Synthetase Activity ◽  
Mitochondrial Enzymes ◽  
Vigorous Exercise ◽  
Ala Synthetase ◽  
Rate Limiting ◽  
Rate Controlling Step ◽  
Mitochondrial Cytochromes

There is evidence that delta-aminolevulinic acid (ALA) synthetase is the rate-limiting enzyme in heme biosynthesis. Accumulation of the apoproteins of the mitochondrial cytochromes appears to be regulated by availability of heme. Exercise and thyrotoxicosis bring about increases in the cytochromes, and in other mitochondrial enzymes, in muscle. In this context, we have examined the effects of exercise and of thyroid hormones on ALA synthetase activity in skeletal muscle. Treadmill running and injection of thyroid hormones both resulted in significant increases in muscle ALA synthetase activity. A rise in ALA synthetase activity was evident within 17 h after a bout of vigorous exercise and 14 h after a single injection of thyroid hormones. The increase in ALA synthetase preceded the increase in cytochrome c, which was used as a mitochondrial marker. These results are compatible with the hypothesis that a relationship exists between heme synthesis and mitochondrial growth in which the rate-controlling step is ALA synthetase activity.

Hepatic stimulator substance: physicochemical characteristics and specificity

1982 ◽  
Vol 242 (3) ◽  
pp. G281-G288 ◽  
Author(s):  
D. R. LaBrecque ◽  
N. R. Bachur
Keyword(s):  
Rat Liver ◽  
Nuclear Dna ◽  
Tritiated Thymidine ◽  
Fold Increase ◽  
Physicochemical Characteristics ◽  
Adult Rats ◽  
Hepatic Stimulator Substance ◽  
Adult Rat ◽  
Heat Stable ◽  
Organ Specific

This laboratory has reported previously that a cytoplasmic extract of weanling or regenerating adult rat liver (but not normal rat liver) will produce a 2.5-fold increase in the incorporation of tritiated thymidine ([3H]dThd) into liver DNA of a 34%-hepatectomized test animal. (J. Physiol. London 248: 273-284, 1975). The present study showed that hepatic stimulator substance (HSS) will stimulate DNA synthesis in normal adult rats and CF1 mice as well. The increased incorporation of [3H]dThd into DNA produced in the normal, nonhepatectomized adult rat was comparable with that induced by a 34% hepatectomy. Autoradiographic studies revealed that the [3H]dThd was incorporated into nuclear DNA and that the stimulation occurred almost exclusively in parenchymal cells. HSS was shown to be heat stable (100 degrees C for 15 min) and was precipitated but not inactivated by alcohol. Ultrafiltration and dialysis studies suggested a molecular weight slightly greater than 10,000. HSS proved to be organ specific, stimulating the liver but not the kidney, bone marrow, or spleen. HSS was found to contain no insulin, glucagon, epidermal growth factor, or peptides of the nonsuppressible insulinlike/multiplication-stimulating activity (somatomedin) group.

Cholestasis is associated with preproenkephalin mRNA expression in the adult rat liver

1995 ◽  
Vol 268 (2) ◽  
pp. G346-G354 ◽  
Author(s):  
N. V. Bergasa ◽  
S. L. Sabol ◽  
W. S. Young ◽  
D. E. Kleiner ◽  
E. A. Jones
Keyword(s):  
Rat Liver ◽  
Northern Blotting ◽  
Cholestatic Liver Disease ◽  
Elevated Plasma ◽  
Bile Duct Resection ◽  
Adult Rats ◽  
Adult Rat ◽  
Hepatocellular Necrosis ◽  
Low Levels ◽  
Experimental Findings

Cholestatic liver disease is associated with clinical and experimental findings consistent with increased opioidergic neuromodulation, increased plasma total opioid activity, and elevated plasma enkephalin concentrations. In contrast to the normal adult rat liver, preproenkephalin mRNA was detected by Northern blotting in livers of adult rats with cholestasis due to bile duct resection and not in the sham-resected controls. Preprodynorphin mRNA was not detected in livers of either group, while preproopiomelanocortin mRNA was found in very low levels in both groups. Preproenkephalin mRNA was not expressed in the livers of rats with acute hepatocellular necrosis induced by thioacetamide. Hybridization histochemistry of cholestatic livers demonstrated the presence of preproenkephalin mRNA primarily over cells in the periportal areas, some of which appeared to be proliferating bile ductular cells. Immunohistochemical staining of cholestatic liver indicated the production of at least Met-enkephalin in association with preproenkephalin gene expression. These findings suggest that the liver itself, by synthesizing enkephalins, contributes directly to the abnormalities of the opioid system reported in cholestasis.

scholarly journals The relationship between palmitoyl-coenzyme A synthetase activity and esterification of sn-glycerol 3-phosphate in rat liver mitochondria

1973 ◽  
Vol 132 (4) ◽  
pp. 697-706 ◽  
Author(s):  
Mariana Sánchez ◽  
David G. Nicholls ◽  
David N. Brindley
Keyword(s):  
Rat Liver ◽  
Specific Activity ◽  
Liver Mitochondria ◽  
Carnitine Palmitoyltransferase ◽  
Rat Liver Mitochondria ◽  
Synthetase Activity ◽  
Palmitoyl Carnitine ◽  
The Mean ◽  
Glycerolipid Synthesis ◽  
Rate Limiting

1. The specific activities for palmitoyl-CoA synthetase and for sn-glycerol 3-phosphate esterification, with palmitoyl-CoA generated either by the endogenous synthetase or from palmitoyl-(-)-carnitine, CoA and excess of carnitine palmitoyltransferase, were measured with rat liver mitochondria. 2. The mean specific activity of palmitoyl-CoA synthetase was approximately five- and seven-fold the rates of sn-glycerol 3-phosphate esterification from palmitate and palmitoyl-(-)-carnitine respectively. No significant correlation was found in different rats between the activities of palmitoyl-CoA synthetase and sn-glycerol 3-phosphate esterification from either acyl precursor. However, there was a significant correlation (r=0.83, P<0.001) between the rates of glycerolipid synthesis from palmitate and palmitoyl-(-)-carnitine. 3. The mean molar composition of the glycerolipid synthesized from palmitate was 58% lysophosphatidate, 31% phosphatidate and 11% neutral lipid. With palmitoyl-(-)-carnitine the equivalent values were 70, 23 and 7%, which were significantly different. 4. When palmitoyl-CoA synthetase had been inactivated by 60–70% after preincubation of mitochondria at 37°C, it became rate-limiting in glycerolipid biosynthesis. Additions of 1–5mm-ATP prevented inactivation of palmitoyl-CoA synthetase. 5. Preincubation also inhibited the oxidation of palmitate, palmitoyl-CoA, palmitoyl-(-)-carnitine and malate plus glutamate. These inhibitions could not be prevented by addition of ATP. 6. Diversion of palmitoyl-CoA to form palmitoyl-(-)-carnitine did not inhibit sn-glycerol 3-phosphate esterification. 7. The palmitoyl-CoA pool synthesized by the palmitoyl-CoA synthetase was augmented by adding partially purified synthetase or carnitine palmitoyltransferase and palmitoyl-(-)-carnitine. No stimulation of palmitate incorporation into glycerolipids occurred. 8. At low concentrations of Mg2+, palmitate, ATP and CoA the velocity with palmitoyl-CoA synthetase decreased more than that of glycerolipid synthesis from palmitate. 9. It is concluded that in the presence of optimum substrate concentrations the activity of sn-glycerol 3-phosphate acyltransferase and not of palmitoyl-CoA synthetase is rate-limiting in the synthesis of phosphatidate and lysophosphatidate in isolated rat liver mitochondria.

scholarly journals A role of asialoglycoproteins for plasma-membrane-induced inhibition of the switching from α1 to β subtypes in adrenergic response during primary culture of rat hepatocytes

1996 ◽  
Vol 316 (3) ◽  
pp. 743-749 ◽  
Author(s):  
Yasuo KAJIYAMA ◽  
Yutaka SANAI ◽  
Michio UI
Keyword(s):  
Primary Culture ◽  
Rat Liver ◽  
Plasma Membranes ◽  
Rat Hepatocytes ◽  
Prior Treatment ◽  
Adult Rats ◽  
Adult Rat ◽  
Liver Membranes ◽  
Young Rat

Adrenergic responses of rat hepatocytes were studied by measuring Ins(1,4,5)P3 (for the response via α1-subtype receptors) and cAMP (for β-subtype response) generation during brief incubation of cells with respective agonists. Hepatocytes from young rats with an age of 1 week displayed a very high β response without a significant α1 response. The β response decreased and the α1 response increased progressively as the age increased; the response was almost exclusively via α1 receptors in hepatocytes of adult rats 9 weeks or more old. The β response developed, again at the expense of the α1 response, in hepatocytes from adult rats during the primary culture at low cell densities [(1–2.5)×104 cells/cm2]. Such ‘α1 to β subtype switching’ of adrenergic responses in vitro was totally inhibited by adding plasma membranes prepared from adult rat liver into the low-cell-density culture, but not inhibited at all by membranes from young rat liver. The inhibitory effect of adult rat liver membranes was lost when the membranes had been exposed to endoglycosidase F or β-galactosidase but was not affected by prior treatment with sialidase. On the contrary, young rat liver membranes became inhibitory to ‘α1 to β subtype switching’ after prior treatment with sialidase. Thus glycoproteins with unsialylated galactosyl termini on the surface of adult rat hepatocytes are likely to function as a determinant of the relative development of α1/β subtypes of adrenergic responses; the β response is predominant in hepatocytes in the juvenile, presumably as a result of sialylation of the galactosyl termini of the functional glycoproteins.

scholarly journals Role of haem in the induction of cytochrome P-450 by phenobarbitone. Studies in chick embryos in ovo and in cultured chick embryo hepatocytes

1981 ◽  
Vol 198 (2) ◽  
pp. 321-329 ◽  
Author(s):  
U Giger ◽  
U A Meyer
Keyword(s):  
Chick Embryo ◽  
Inhibitory Effect ◽  
Chick Embryos ◽  
In Ovo ◽  
Haem Biosynthesis ◽  
Rate Limiting ◽  
Cytochrome P 450 ◽  
Hepatic Cytochrome

The role of haem synthesis during induction of hepatic cytochrome P-450 haemoproteins was studied in chick embryo in ovo and in chick embryos hepatocytes cultured under chemically defined conditions. 1. Phenobarbitone caused a prompt increase in the activity of 5-aminolaevulinate synthase, the rate-limiting enzyme of haem biosynthesis, and in the concentration of cytochrome P-450. This induction response occurred without measurable initial destruction of the haem moiety of cytochrome P-450. 2. When intracellular haem availability was enhanced by exogenous haem or 5-aminolaevulinate, phenobarbitone-medicated induction of cytochrome P-450 was not affected in spite of the well known repression of 5-aminolaevulinate synthase by haem. These data are consistent with the concept that haem does not regulate the synthesis of cytochrome P-450 haemoproteins. 3. Acetate inhibited haem biosynthesis at the level of 5-aminolaevulinate formation. When intracellular haem availability was diminished by treatment with acetate, phenobarbitone-medicated induction was decreased. 4. This inhibitory effect of acetate on cytochrome P-450 induction was reversed by exogenous haem or its precursor 5-aminolaevulinate. These data suggest that inhibition of haem biosynthesis does not decrease synthesis of apo-cytochrome P-450. Moreover, they indicate that exogenous haem can be incorporated into newly formed aop-cytochrome P-450.

scholarly journals Protein degradation in rat liver during post-natal development

1980 ◽  
Vol 192 (1) ◽  
pp. 321-330 ◽  
Author(s):  
S M Russell ◽  
R J Burgess ◽  
R J Mayer
Keyword(s):  
Protein Degradation ◽  
Rat Liver ◽  
Pyruvate Dehydrogenase ◽  
Mitochondrial Outer Membrane ◽  
Intermembrane Space ◽  
Adult Rats ◽  
Adult Rat ◽  
Mitochondrial Inner Membrane ◽  
Degradation Rates ◽  
A Subunit

Protein degradation rates for liver subcellular and submitochondrial fractions from neonatal (8-day), weanling (25-day) and adult rats were estimated by the double-isotope method with NaH14CO3 and [3H] arginine as the radiolabelled precursors [Dice, Walker, Byrne & Cardiel (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 2093-2097]. Decreased protein degradation rates were found during post-natal development for homogenate, nuclear, mitochondrial, lysosomal and microsomal proteins. A decrease in degradation rates for the immunoisolated subunits of monoamine oxidase and pyruvate dehydrogenase was also observed in neonatal and weanling rats respectively. The results suggest coordinate degradation of the subunits of the multi-subunit enzyme pyruvate dehydrogenase. Pyruvate dehydrogenase has a faster rate of degradation in adult rat liver than does cytochrome oxidase. Data analysis suggests heterogeneity of protein degradation rates in the mitochondrial outer membrane and intermembrane space fractions at each developmental stage but not in the mitochondrial inner membrane or matrix fractions. Results obtained for protein degradation rates in adult rat liver by the method of Burgess, Walker & Mayer [(1978) Biochem. J. 176, 919-926] in general confirmed the results obtained for the adult rat liver by the above method. No evidence of a subunit-size relationship for protein degradation was found for proteins in any subcellular or submitochondrial fraction.

scholarly journals Palmitate activation and esterification in microsomal fractions of rat liver

1975 ◽  
Vol 152 (1) ◽  
pp. 39-49 ◽  
Author(s):  
K A Lloyd-Davies ◽  
D N Brindley
Keyword(s):  
Rat Liver ◽  
Maximum Rate ◽  
Microsomal Fraction ◽  
Synthetase Activity ◽  
Optimum Conditions ◽  
Glycerol Phosphate ◽  
Glycerolipid Synthesis ◽  
The Relationship ◽  
Rate Limiting ◽  
Substrate Concentrations

1. Palmitoyl-CoA synthetase activity in the microsomal fraction of rat liver was measured directly by palmitoyl-CoA production, and indirectly by converting the palmitoyl-CoA into palmitoylcarnitine under optimum conditions. Even in the latter system, palmitoyl-CoA accumulated. The rate of palmitoyl-CoA hydrolysis and the inhibition of palmitoyl-CoA synthetase by palmitoyl-CoA were each estimated to be less than 10% of the maximum rate of palmitoyl-CoA production. The concentration of palmitoyl-CoA present in the assay systems used for measuring palmitate esterification to glycerol phosphate and the activity of palmitoyl-CoA synthetase by using the carnitine-linked determination were measured. These concentrations were not altered by the addition of glycerol phosphate, or of carnitine plus carnitine palmitoyltransferase. The relationship between the activity of palmitoyl-CoA synthetase and the rate of glycerolipid synthesis was investigated. The latter activity was measured by using palmitoyl-CoA generated from palmitate, palmitoyl-AMP or palmitoylcarnitine. It is concluded that, at optimum substrate concentrations, the activity of glycerol phosphate acyltransferase is rate-limiting in the synthesis of phosphatidate by rat liver microsomal fractions. The implications of these results in the measurement of palmitoyl-CoA synthetase and in the control of glycerolipid synthesis are discussed.

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