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At least 919 records · Page 51Linked to original sources
PubMed1988

Placental amino acid uptake in normal and complicated pregnancies.

Amino acids are the essential substrates for fetal growth and catabolism. The fetus is dependent on the placenta for the provision of amino acids, the first step being concentration of amino acids within the syncytiotrophoblast for subsequent transfer to the fetus. A reliable technique for the isolation of human syncytiotrophoblast plasma membrane has been described, and the suitability of this preparation for the study of amino acid uptake and membrane transport has been well documented. Using this technique, the microvillous vesicle uptake of alpha-aminoisobutyric acid (AIB), a nonmetabolizable amino acid, has been determined over multiple time points for normal (NL) pregnancies and those complicated by pregnancy-induced hypertension (PIH), non-insulin-dependent diabetes mellitus (NIDDM) and those delivering small-for-gestational-age (SGA) neonates. There was no significant difference in AIB uptake between NL pregnancies and those complicated by PIH or NIDDM. Compared to each of the above, AIB uptake by the SGA group was significantly less at each time point. These results suggest that normal placental amino acid transport mechanisms may be altered in SGA pregnancies. If so, such alterations may interfere with the normal provision of nutrients to the fetus and ultimately contribute to impaired growth in utero.

Adult↗
PubMed1987

Effect of insulin-like growth factor-I on metabolism in bovine mesenteric arteries.

The effect of insulin-like growth factor-I (IGF-I) on glucose accumulation, amino acid uptake and incorporation of amino acid into protein was studied in arterial smooth muscle. Accumulation of [14C]glucose, uptake of [14C]alpha-aminoisobutyric acid (AIB) and incorporation of [14C]phenylalanine into protein were measured in intima-media preparations of bovine mesenteric arteries (BMA) incubated with IGF-I for 2, 4 or 6 h. IGF-I (2.2 nmol l-1) increased the accumulation of glucose into BMA after 4 h (P = 0.0079) and 6 h incubation (P = 0.0027) and in a concentration of 22 nmol l-1) also after 2 h (P = 0.015). The uptake of AIB and the incorporation of phenylalanine were increased after 4 h incubation with 2.2 nmol l-1) IGF-I (P = 0.0045 and P = 0.026, respectively). The effects of IGF-I on all of the metabolic parameters were dependent on incubation time and concentration of IGF-I. Concentration-effect curves were determined for the effect of IGF-I and also for insulin on glucose accumulation in BMA incubated for 6 h. The concentration-effect relationships for IGF-I and insulin were very similar with pD2 values of 7.6 +/- 0.2 (EC50 = 27 nmol l-1) and 7.5 +/- 0.2 (EC50 = 34 nmol l-1), respectively. No additive effect of IGF-I and insulin in supra-physiological concentrations (1.0 mumol l-1) could be demonstrated. These results show that IGF-I has metabolic effects which are similar to the effects of insulin in vascular smooth muscle and suggest that IGF-I may be of importance for the metabolism in vascular smooth muscle.

Aminoisobutyric Acids↗
PubMed1999

Long-range electron transfer in rigid 3(10)-helical oligopeptides containing redox cyclic alpha-amino acids.

Intrahelical photoinduced electron transfer processes (ET) in conformationally restricted oligopeptides have been studied by nanosecond time-resolved transient spectroscopy. The helical peptides were constructed from sterically hindered alpha-aminoisobutyric acid (Aib) and two cyclic alpha-amino acids (Aib class) bearing electron acceptor and donor side chains (DkNap, ThQx). This helical backbone design provides high conformation stability, as previously demonstrated, and yields reliable 3(10)-helical architectures in solution. The forward ET between ThQx and 3DkNap is followed by a slow back ET thus giving rise to an accumulation of the charge-separated ion pairs for hundreds of nanoseconds. We demonstrate the modulation of electronic interactions by the number of intervening Aib residues separating acceptor-donor side chains and propose modifications of the peptide framework by inclusion of a non-Aib amino acid residue. These well-defined and sterically stable frameworks are suited for the precise evaluation of intrahelical electron transfer processes mediated by peptides.

Aminoisobutyric Acids↗
PubMed1979

Catabolic control of the enhanced alanine-preferring system for amino acid transport in glucose-starved hamster cells requires protein synthesis.

In cultured hamster cells starved for glucose for 24 hr there is an enhancement of the rate of alpha-aminoisobutyric acid transport ("shiftup"). When the starved cells are re-fed with glucose, the rate of transport shifts back down to the low, "regulated" rate typical of cells continuously fed with medium containing glucose ("shiftdown"). The high, deregulated rate of transport is maintained, however, when cycloheximide is present for 24 hr during the re-feeding with glucose. Maintenance of the high transport rate is evident only when the cells are incubated in amino acid-free medium just prior to the transport assay or when the assays are conducted with isolated membrane vesicles. A premature, pseudoshiftdown was observed in intact cells within as little as 2 hr after re-feeding when care was not taken to deplete the amino acid pool prior to the transport assay. In addition, a cycloheximide-insensitive increase in transport was observed when cultures were re-fed for 2 hr with amino acid-free medium containing fresh serum. These results emphasize the often overlooked precautions that should be taken to guard against artifacts that could mislead interpretations of amino acid transport data. More important, however, is the finding that Na(+)-dependent amino acid transport in cultured animal cells is regulated in part by a factor (or factors) that becomes inactivated when the cells are maintained under nonglycolytic culture conditions. In order to reactivate the control mechanism, starved cells that have been re-fed with glucose must resynthesize the regulatory factor(s). Thus, in at least cultured hamster cells, Na(+)-dependent amino acid transport regulation is much like the hexose transport regulation in that catabolic control (shiftdown) requires protein synthesis.

Alanine↗
PubMed1980

Cytotoxicity as an indicator for transport mechanism: evidence that murine bone marrow progenitor cells lack a high-affinity leucine carrier that transports melphalan in murine L1210 leukemia cells.

Cytotoxicity of melphalan to murine L1210 leukemia cells was reduced to a limiting maximum value of 50% by 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid (BCH), indicating that cytotoxicity is partially dependent on drug uptake by system L. L-Leucine, but not alpha-aminoisobutyric acid (AIB), completely reduced the remaining 50% of drug cytotoxicity. These results contrast with those obtained with a sensitive host tissue, the bone marow progenitor cells of the white cell series (CFU-C), in that a high-affinity leucine transport system corresponding to system L was not identified.

Aminoisobutyric Acids↗
PubMed1979

Amino acid transport in the exocrine pancreas. IV. Do glucagon or insulin mediate the in vivo effect of caerulein on amino acid transport and incorporation?

The direct in vitro effect of caerulein on pancreatic protein synthesis and amino acid transport has been investigated. In contrast to in vivo conditions we were unable to demonstrate any effect on alpha-aminoisobutyric acid and leucine uptake and on leucine incorporation usin rat pancreatic lobules. Insulin and glucagon were therefore examined as possible mediators for the in vivo effect of caerulein. Insulin (1--5 microM) slightly enhanced AIB uptake (16% but did not change uptake and incorporation of leucine. Glucagon (0.01--1 microM) was ineffective. Both islet hormones had no influence on the formation of cyclic GMP induced by secretagogue either in rat (40% increase) or in guinea pig lobules (500% increase). It seems unlikely that the two islet hormones exert any direct effect on the exocrine pancreas and thus could serve as mediators for the in vivo synthetic effect of caerulein.

Aminoisobutyric Acids↗
PubMed1979

Somatostatin: lack of effect of cyclic AMP release and amino acid transport in isolated rat hepatocytes.

The aim of the present study was to determine whether or not somatostatin can directly affect amino acid transport and cyclic AMP (cAMP) release in isolated rat hepatocytes. Somatostatin at 1.5 microgram/ml (1mumol/l) had no effect on basal uptake of alpha-aminoisobutyric acid (AIB). Similarly, the peptide was without effect on basal cAMP release. Somatostatin exerted a slight but statistically not significant inhibitory effect on glucagon-stimulated AIB uptake and cAMP release. These observations do not support the possibility that somatostatin might directly interfere with hepatic glucose metabolism by altering the entry of amino acids into the liver and--or--by affecting the level of endogenous cAMP.

Aminoisobutyric Acids↗
PubMed1991

Increased insulin responsiveness in isolated rat hepatocytes incubated with free fatty acid-poor albumin.

Freshly isolated rat hepatocytes incubated in a medium containing bovine serum albumin partially purified by charcoal treatment at pH 3 are three times more responsive to insulin with regard to alpha-aminoisobutyric acid uptake than those incubated in medium containing regular bovine serum albumin. This finding should facilitate future work in isolated hepatocytes, a cell system that for the most part has been considered relatively unresponsive to insulin.

Aminoisobutyric Acids↗
PubMedDate not supplied

Insulin-like growth factor I (IGF-I) stimulates glucose and amino acid uptake in cultured glomerular mesangial cells.

Cultured mesangial cells possess a large number of receptors specific to IGF-I with a small number of insulin receptors. Physiological concentrations of IGF-I increased the uptakes of aminoisobutyric acid and 2-deoxyglucose in mesangial cells, while insulin exhibited similar effects only with unphysiologically high concentration. These findings suggest that, in cultured mesangial cells, IGF-I may regulate cellular metabolic functions such as glucose and amino acid uptakes through its own receptors rather than insulin receptors.

Aminoisobutyric Acids↗
PubMed1981

The effect of reagents that increase membrane fluidity on the activity of 3-hydroxyl-3-methyl glutaryl coenzyme A reductase in the CHO-K1 cell.

The compounds cetyl trimethyl ammonium bromide (CTAB) and ethanol both decrease the order parameter of a spin probe embedded in cholesterol-lecithin liposomes, but CTAB produces lowering of the order parameter comparable to that produced by ethanol at a 10,000-fold lower concentration. Treatment of CHO-K1 cells with CTAB or ethanol at concentrations that produce comparable increases of membrane fluidity produce to 2- to 3-fold increase of microsomal membrane cholesterol to phospholipid ratio and a 2- to 3-fold increase of the activity of the rate-limiting enzyme of cholesterol biosynthesis, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase. Cells treated with CTAB or ethanol show a progressively decreasing capacity to accumulate alpha-aminoisobutyric acid with increasing drug treatment, but cells pre-treated with CTAB are relatively resistant to the effects of CTAB on alpha-aminoisobutyrate transport. The increase in HMG-CoA reductase by CTAB or ethanol is not observed when these compounds are added directly to cell extracts but, rather, is only observed after 8 hours or exposure of intact cells to these drugs. Actinomycin D and cycloheximide treatment prevent the increase in enzyme activity, and the increase is also blocked in a regulatory mutant of the CHO-K1 cell with permanently repressed HMG-CoA reductase activity. These data are consistent with a homeoviscous adaptation mechanism in the CHO-K1 cell, in which increased activity of HMG-CoA reductase, through a process requiring RNA and protein synthesis, compensates for conditions that increase membrane fluidity by increased cellular cholesterol biosynthesis and cholesterol to phospholipid ratio.

Aminoisobutyric Acids↗
PubMed1990

Microvascular specializations promoting rapid interstitial solute dispersion in nucleus tractus solitarius.

Nucleus tractus solitarius (NTS), an aggregate of several individual nuclear groups in the dorsal medulla oblongata, is involved in virtually all autonomic functions as the first synaptic site in the brain for many peripheral viscerosomatic inputs. We found morphological evidence that dorsocaudal subregions of rat NTS (approximately 800 microns caudal from obex) had fenestrated capillaries and enlarged Virchow-Robin (perivascular) spaces that were similar to those in area postrema but unlike capillaries elsewhere in the medulla oblongata. Complexes of microvessels, consisting of up to 10 small vessels with smooth muscle layers (luminal diameters of 10-45 microns) and several capillaries (average luminal diameter of 4.5 microns), were located in the dorsal midline of NTS within large Virchow-Robin spaces measuring some 2,000 microns 2 in area. In physiological studies, we determined that most of NTS had a definable blood-brain barrier [permeability-surface area (PS) products for a neutral amino acid near 0], but medial and lateral aspects of the commissural subnucleus of NTS had PS products of 16-63 microliters.g-1.min-1 for alpha-[14C]aminoisobutyric acid 12 s after intravenous injection. Microvascular differentiations permitting such brisk tracer influx from blood resemble those of area postrema and appear to afford the rich neuropil of commissural NTS with a constant stream of blood-borne information for expediting its regulation of viscerosensory and autonomic functions.

Aminoisobutyric Acids↗