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Biomedical subjects

A Ichihara

Publications and source records attributed to A Ichihara.

At least 217 records · Page 12Linked to original sources
PubMed1982

Regulatory relation between insulin receptor and its functional responses in primary cultured hepatocytes of adult rats.

The relation between changes of insulin receptor and various metabolic responses were studied in adult rat hepatocytes in primary culture. In cells cultured for 3 h without insulin, the number of high affinity sites and the dissociation constant (Kd) of insulin receptor, determined from a Scatchard plot, were 1.05 x 10(5) sites/cell and 1.5 x 10(-9) M, respectively. The receptor number increased 2-fold, but the Kd value remained constant during 2-days culture in insulin-free medium (up-regulation). Addition of dexamethasone (Dex), growth hormone, glucagon or triiodothyronine did not change the number of insulin receptors or the Kd value. In contrast, 1-day culture in insulin (1 x 10(-7) M) medium decreased the receptor number by half (down-regulation) without change of the Kd value. Short-term responses of glycogenesis, amino acid transport and lipogenesis by insulin increased as the receptor number increased. In these cases, the sensitivity to insulin (Ka: half dose for the maximum response) did not change in cells with different receptor numbers, but the maximum response changed. These results show that hepatocytes, unlike adipocytes, do not have spare receptors of insulin. During down-regulation, the receptor number decreased by only half, but the insulin responses were lost almost completely. The receptor number returned to the normal level after culture in insulin-free medium for 12 h, but recovery of the responses took longer, suggesting that for the insulin response not only change of receptor number, but also other regulatory mechanisms for post-receptor processes, such as desensitization, are involved.

Animals↗
PubMed1982

Role of serum in maintenance of functional hepatocytes in primary culture.

Serum at 5 to 10% is required for maintenance of functional adult rat hepatocytes in primary culture. One effect of the serum is to induce attachment and spreading of hepatocytes on plates as monolayers. Another role is to maintain cell viability for over 2 days. For the first effect, serum could be replaced completely by fibronectin (Fn). The effects of Fn on attachment and spreading of cells were dose-dependent and maximum at 10 micrograms/ml. Cells in serum-free medium on Fn-coated dishes showed similar activities of glycogenolysis and glycogenesis to cells cultured in medium containing 5% calf serum on untreated dishes in response to glucagon, dibutyryl cyclic AMP (bt2c AMP), isoproterenol and insulin. The increase in alkaline phosphatase [EC 3.1.3.1] activity and induction of tyrosine aminotransferase [EC 2.6.1.5] by dexamethasone (Dex) in cells under the two conditions were also similar. However, the inductions of tryptophan oxygenase [EC 1.13.11.11] by Dex, glucagon, and bt2cAMP were 4-7 times higher in cells cultured in serum-free medium. The inductions by Dex plus glucagon in the two types of cultures were inhibited similarly by insulin. In serum-free medium containing Dex and insulin in Fn-coated dishes, the cells survived as monolayers for about 50 h without detachment from the dishes, but for longer survival it was necessary to add 5% serum to the medium. A fraction with a molecular weight of over 50,000 from serum was separated by ultrafiltration and this fraction showed a similar effect to serum in increasing survival. A similar factor, but with about 70 times higher specific activity, was found in an extract of bovine pituitary gland.

Animals↗
PubMed1982

Stereospecific conversion of 1-aminocyclopropanecarboxylic Acid to ethylene by plant tissues : conversion of stereoisomers of 1-amino-2-ethylcyclopropanecarboxylic Acid to 1-butene.

Inasmuch as the molecule of 1-aminocyclopropanecarboxylic acid (ACC) possesses reflective symmetry but lacks rotational symmetry, the two chemically alike methylene groups can be distinguished by a stereospecific enzyme. To determine whether ACC conversion to ethylene by plant tissues proceeds in a stereospecific fashion, the four stereoisomers of 1-amino-2-ethylcyclopropanecarboxylic acid (AEC) were administered to postclimacteric apple (Malus sylvestris Mill., var. Golden Delicious), excised preclimacteric cantaloupe (Cucumis melo L., var. reticulatis Naud cv. PMR-45), and etiolated mung bean (Vigna radiata L., Wilczek, var. Berken) hypocotyls. In each case (1R,2S)-AEC was the preferred substrate yielding 1-butene. In contrast, all AEC isomers were converted equally well to butene by chemical oxidation using NaOCl. Both ACC and AEC appear to be substrates for the same enzyme since both reactions are inhibited in parallel by N(2) or Co(2+), both reactions are induced in parallel by excision, and when both substrates are present simultaneously each will act as an inhibitor with respect to the other. The aforementioned observations indicate that ACC is stereospecifically converted to ethylene. For AEC to be the most active precursor of 1-butene, the ethyl substituent should be trans to the carboxyl group and the pro-(S) methylene group should be unsubstituted. This observation leads to the suggestion that the enzyme interacts with amino, carboxyl, and pro-(S) methylene groups, a configuration corresponding to a l-amino acid. This view is consistent with the observation that the l-forms of alanine and methionine inhibit the conversion of ACC to ethylene more than the corresponding d-amino acids in the mung bean hypocotyl system.

Journal Article↗
PubMed1982

Clinical value of the determination of serum guanase activity. Studies on patients and experimental data from mongrel dogs and cultured rat hepatocytes.

Serum guanase activity was measured by a new method and compared with serum glutamic oxalacetic transaminase and glutamic pyruvic transaminase levels in 150 patients with various disorders, 21 dogs with experimental myocardial infarction, and 2 CCl4-treated dogs. Additionally, studies of the effect of CCl4 on enzyme release were undertaken using cultured rat hepatocytes. Glutamic oxalacetic transaminase, glutamic pyruvic transaminase, and guanase activities were found to be significantly elevated in patients with various liver disorders, those with acute myocardial infarction with prominent congestion of the liver, and also in CCl4-treated dogs. However, serum guanase activity was normal in patients with a variety of non-liver-related diseases including acute myocardial infarction, and in dogs with experimental myocardial infarction without liver damage, even when the serum glutamic oxalacetic transaminase and glutamic pyruvic transaminase activities were increased. The glutamic oxalacetic transaminase, glutamic pyruvic transaminase, and guanase activities in the culture medium of rat hepatocytes indicated in the presence of 0.5 mM CCl4 were elevated. These findings indicate that serum guanase activity is a more specific indicator of liver damage than serum glutamic oxalacetic transaminase and glutamic pyruvic transaminase.

Alanine Transaminase↗
PubMed1981

Hormonal control of the development of tryptophan oxygenase in primary cultures of young rat hepatocytes.

Developmental increase of tryptophan oxygenase (L-tryptophan: oxygen 2, 3-oxidoreductase (decyclizing), EC 1.13.11.11) was studied using hepatocytes of neonatal rats in primary culture. Hepatocytes from rats of 2-30-days-old were isolated and cultured for 2 days. In cultured hepatocytes of 2-day-old rats, tryptophan (2.5 mM), dexamethasone (1 x 10(-5) M) and glucagon (1 x 10(-7) M) did not cause the appearance of tryptophan oxygenase. But the enzyme activity became detectable, when hepatocytes from 5-day-old rats were incubated with tryptophan, the oxygenase could be induced precociously by dexamethasone, but by glucagon. The effect of glucagon was first seen 2 weeks after birth. However, in hepatocytes of 9-day-old rats glucagon stimulated formation of cyclic AMP and protein kinase activity (EC 2.7.1.37) and also induced tyrosine aminotransferase (EC 2.6.1.5). When hepatocytes of 9-day-old rats were cultured for 4 days, their tryptophan oxygenase became inducible by glucagon. Insulin almost completely inhibited precocious appearance of the enzyme activity evoked by tryptophan plus dexamethasone in hepatocytes of 9-day-old rats. These studies suggest that the appearance of tryptophan oxygenase in rat liver during development is due to first the onset of gene coding for tryptophan oxygenase and then stimulation by the sequential actions of glucocorticoid and glucagon.

Animals↗
PubMed1980

Induction of L-lysine-2-oxoglutarate reductase by glucagon and glucocorticoid in developing and adult rats: in vivo and in vitro studies.

L-Lysine-2-oxoglutarate reductase (EC 1.5.1.8, NADP) in the liver of adult rats increased 4-5 times when the animals were treated with alloxan. In diabetic rats injection of insulin or adrenalectomy prevented the increase in enzyme activity. The activity of the similar enzyme in kidney was not changed by these treatments. The enzyme activity in primary cultured adult rat hepatocytes was also induced by addition of dexamethasone and glucagon together, and glucagon could be replaced by dibutyryl cyclic AMP. Insulin inhibited the induction. The hormonal induction was also inhibited by actinomycin D and by cycloheximide. During development of rats, fetal liver showed very low activity, but the activity appeared on day 1 after birth and then increased rapidly, reaching the adult level by day 5. The activity of the kidney enzyme increased more slowly and reached adult level 1 month after birth. Intra-uterine injection of glucagon caused precocious induction of the liver enzyme in fetuses. These results indicate that the activity of L-lysine-2-oxoglutarate reductase in the adult liver and in part in neonatal liver also, in controlled by both glucagon and glucocorticoid.

Adrenal Glands↗
PubMed1980

Insulin and glucagon as a new regulator system for tryptophan oxygenase activity demonstrated in primary cultured rat hepatocytes.

The basal activity of tryptophan 2,3-dioxygenase (EC-1.13.11.11) in primary cultured rat hepatocytes decreased during culture, but addition of either tryptophan (2.5 x 10(-3) M) or dexamethasone (1 x 10(-6) M) could prevent the decrease. Addition of both compounds caused severalfold induction of activity. Glucagon (1 x 10(-8) M) alone did not induce the activity, but its inductive effect in combination with tryptophan was similar to that of tryptophan plus dexamethasone. The effect of glucagon was additive with those of tryptophan and dexamethasone and hence the highest induction (7-fold) was achieved by addition of all three inducers. Glucagon could be replaced by dibutyryl cyclic AMP (1 x 10(-5) M). Insulin (1 x 10(-8) M) inhibited the inductions by glucagon and dexamethasone, but not that by tryptophan. Cycloheximide inhibited the inductions by all three inducers, but actinomycin D inhibited only the induction by dexamethasone. These results suggest that the three compounds have different mechanisms of induction of tryptophan oxygenase activity: tryptophan prevents enzyme inactivation, dexamethasone may stimulate enzyme synthesis at the level of transcription, and glucagon may enhance the synthesis at the translational level.

Animals↗
PubMed1980

Biochemical functions of adult rat hepatocytes in primary culture.

Liver parenchymal cells from adult rats were isolated by treatment with collagenase and cultured as monolayers in Williams medium E with 10% fetal or calf serum. The additions of dexamethasone and insulin to the medium were essential for maintaining liver functions of the cells. These cells synthesized and secreted various serum proteins into the medium. Gluconeogenesis and glycogenolysis were enhanced by glucagon, and lipogenesis was stimulated by insulin. Many enzymes were also induced by various hormones. These activities were very low in freshly isolated cells, but were restored when the cells were cultured for a few days. Markers of plasma membranes, such as 5'-nucleotidase and insulin receptors, were reduced to half the normal levels on freshly isolated cells, but they were restored to the normal levels during culture of the cells without added hormones. Analysis of the profile of amino acids in the medium showed that freshly isolated cells were in a catabolic state of protein turnover and released branched chain amino acids into the medium, but that cultured cells consumed amino acids, not only for protein synthesis, but also for other metabolic processes, such as gluconeogenesis. These findings show that freshly isolated cells have impaired functions and are unsuitable for use in studies of liver metabolism, but that after culture for a few days the cells regain the activity of normal liver and hance become useful for studies of liver functions. Studies with these cells are simpler and give clear results than studies in vivo.

Amino Acids↗