scholarly journals Regulation of tyrosine aminotransferase in foetal rat liver

1980 ◽  
Vol 186 (2) ◽  
pp. 609-612 ◽  
Author(s):  
S M Andersson ◽  
N C Räihä ◽  
J J Ohisalo
Keyword(s):  
Enzyme Activity ◽  
Methyl Ester ◽  
Cyclic Amp ◽  
Organ Culture ◽  
Rat Liver ◽  
Tyrosine Aminotransferase ◽  
Dibutyryl Cyclic Amp ◽  
Adult Rat ◽  
Foetal Rat

A specific tyrosine aminotransferase, separate from the aspartate aminotransferases, is present in low concentration in foetal rat liver at the 21st day of gestation. Intraperitoneal injections of tyrosine methyl ester into the foetuses in utero increase the activity 2-fold, whereas glucose injections decrease it. Tyrosine, dexamethasone and dibutyryl cyclic AMP induce the enzyme activity in organ culture to the same extent as in adult rat liver in vivo.

scholarly journals Changes in the activities of the enzymes of urea synthesis caused by dexamethasone and dibutyryladenosine 3′:5′-cyclic monophosphate in foetal rat liver maintained in organ culture

1976 ◽  
Vol 160 (2) ◽  
pp. 159-162 ◽  
Author(s):  
E Edkins ◽  
N C R Rïhä
Keyword(s):  
Cyclic Amp ◽  
Organ Culture ◽  
Rat Liver ◽  
Urea Cycle ◽  
Defined Medium ◽  
Urea Synthesis ◽  
Dibutyryl Cyclic Amp ◽  
Carbamoyl Phosphate ◽  
Foetal Rat ◽  
Ornithine Transcarbamoylase

Liver explants from 19-day foetal rats were maintained in organ culture, in a defined medium, for up to 48h. Both 6-N,2′-O-dibutyryl cyclic AMP, in the presence of theophylline, and dexamethasone caused an increase in the activities of carbamoyl phosphate synthase, argininosuccinate synthetase, argininosuccinate lyase and arginase. These increases could be abolished by simultaneously incubating the explants with cycloheximide. No change in the activity of ornithine transcarbamoylase was found with either hormone. Previous work has shown that injection of corticosteroids into 19.5-day foetal rats in utero did not cause an increase in the arginine synthetase system. Present results suggest that this lack of effect is not due to any incompetence of the foetal rat liver at this stage to respond to this agent. The observations on ornithine transcarbamoylase activity suggest that this enzyme is induced in the liver of the perinatal rat by neither corticosteroids nor hormones acting via cyclic AMP, and it may be that all the enzymes of the urea cycle are induced physiologically by an agent or agents as yet unidentified.

scholarly journals Regulation of coenzyme A biosynthesis by glucagon and glucocorticoid in adult rat liver parenchymal cells

1980 ◽  
Vol 188 (1) ◽  
pp. 175-184 ◽  
Author(s):  
Colleen M. Smith ◽  
C. Richard Savage
Keyword(s):  
Cyclic Amp ◽  
Rat Liver ◽  
Maximum Effect ◽  
Maximal Effect ◽  
Dibutyryl Cyclic Amp ◽  
Liver Parenchymal ◽  
Adult Rat ◽  
Intracellular Mechanism ◽  
Inhibitor Of Protein Synthesis ◽  
Parenchymal Cells

We studied the effects of glucagon, dibutyryl cyclic AMP and dexamethasone on the rate of [14C]pantothenate conversion to CoA in adult rat liver parenchymal cells in primary culture. The presence of 30nm-glucagon increased the rate by about 1.5-fold relative to control cultures (range 1.4–2.3) and 2.4-fold relative to cultures containing 1–3m-i.u. of insulin/ml. The half-maximal effect was obtained at 3nm-glucagon. Dibutyryl cyclic AMP plus theophylline also enhanced the rate by about 1.5-fold. Dexamethasone acted synergistically with glucagon; glucagon at 0.3nm had no effect when added alone, but resulted in a 1.7-fold enhancement when added in the presence of dexamethasone (maximum effect at 50nm). The 1.4-fold enhancement caused by the addition of saturating glucagon concentrations was increased to a 3-fold overall enhancement by the addition of dexamethasone. However, dexamethasone added alone over the range 5nm to 5μm had no effect on the rate of [14C]pantothenate conversion to CoA. The stimulatory effect of dibutyryl cyclic AMP plus theophylline was also enhanced by the addition of dexamethasone. Changes in intracellular pantothenate concentration or radioactivity could not account for the stimulatory effects of glucagon, dibutyryl cyclic AMP or dexamethasone. Addition of 18μm-cycloheximide, an inhibitor of protein synthesis, decreased the rate of incorporation of [14C]pantothenate into CoA and the enhancement of this rate by glucagon and dibutyryl cyclic AMP plus theophylline in a reversible manner. These results demonstrate an influence of glucagon, dibutyryl cyclic AMP and glucocorticoids on the intracellular mechanism regulating total CoA concentrations in the liver.

scholarly journals Influence of glucagon, 6-N,2′-O-dibutyryladenosine 3′:5′-cyclic monophosphate and triamcinolone on the arginine synthetase system in perinatal rat liver

1972 ◽  
Vol 126 (1) ◽  
pp. 89-98 ◽  
Author(s):  
A L. Schwartz
Keyword(s):  
Cyclic Amp ◽  
Rat Liver ◽  
Cyclic Nucleotide ◽  
Time Course ◽  
Fold Increase ◽  
Dibutyryl Cyclic Amp ◽  
System Activity ◽  
Cyclic Monophosphate ◽  
Foetal Rat ◽  
Postnatal Rats

1. The administration of triamcinolone (19–190μg/animal) to postnatal rats increased the arginine synthetase system activity 1.2–2.5-fold above control values 24h after exposure to the hormone. Cortisol (hydrocortisone), however, increased the arginine synthetase system activity only when larger (190μg/animal) or repeated daily doses were given. Glucagon (100μg/animal) stimulated arginine synthetase system activity only after the second postnatal day. None of these agents increased the activity in 19.5–21.5-day foetuses after intrauterine administration. 2. The viability of foetal rat liver explants maintained in organ culture for up to 54h was validated both by ultramicroscopic examination and by incorporation of radioactive leucine and orotic acid. 3. In organ cultures of foetal rat liver explants (18.5 days to term), triamcinolone (20μg/ml of medium) evoked a 2.8–4.3-fold increase after 24h of incubation. This increase was completely inhibited by actinomycin D (25μg/ml) or cycloheximide (10μg/ml). Cortisol (5–50μg/ml) or glucagon (0.067–67μg/ml) also increased the arginine synthetase system activity above the respective control values, but there was no increase in activity with insulin (0.05–0.25i.u./ml). 4. Maximum concentrations of glucagon (67μg/ml), dibutyryl cyclic AMP (6-N,2′-O-dibutyryladenosine 3′:5′-cyclic monophosphate) (0.1mm) and triamcinolone (20μg/ml) incubated for 24h with foetal rat liver explants each produced between a two-and three-fold increase in the activity of the arginine synthetase system. Combinations of maximum amounts of glucagon and the cyclic nucleotide did not produce a greater effect than either agent alone. However, the combination of dibutyryl cyclic AMP with triamcinolone appeared to produce somewhat less than additive effects. 5. The effects of the cyclic nucleotide and triamcinolone were evident after 12h of incubation and increased steadily throughout the 24h of observation. This time-course of increased enzyme activity is very much slower than that reported for the induction of other enzymes in explant cultures of foetal rat liver.

scholarly journals Stabilization of rat liver tyrosine aminotransferase in vivo by pyridoxine administration

1980 ◽  
Vol 186 (2) ◽  
pp. 625-627 ◽  
Author(s):  
B M Snape ◽  
A A Badawy ◽  
M Evans
Keyword(s):  
Cyclic Amp ◽  
Rat Liver ◽  
Tyrosine Aminotransferase ◽  
Mechanisms Of Action

Administration of pyridoxine stabilizes rat liver tyrosine aminotransferase in vivo, whereas administration of cortisol, cyclic AMP, glucagon, insulin, tryptophan or tyrosine does not. The results of these and other experiments with pyridoxine are discussed in relation to the mechanisms of action of this vitamin on the activity of the enzyme.

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