Stimulation of renal amino acid reabsorption after treatment with triiodothyronine or dexamethasone in amino acid loaded rats

Summary In adult female anaestetized rats, the influence of triiodothyronine or dexamethasone on renal amino acid handling was investigated in leucine (20mg/100g b.wt.) or glutamine (45mg/100g b.wt.) loaded animals. Bolus injections of both amino acids were followed by temporary increase in fractional excretion of the administered amino acids as well of the endogenous amino acids which were not administered.Under load conditions (leucine and glutamine), dexamethasone treatment (60 g/100 g b.wt. for 3 days, i.p. once daily) was followed by a stimulation of renal amino acid reabsorption. The increase in fractional amino acid excretion after amino acid load was significantly lower than in untreated rats. The effect of triiodothyronine (20,g/1008 b.wt. for 3 days, i.p. once daily) was different in leucine and glutamine loaded animals: after leucine bolus injection a comparable stimulatory effect as shown for dexamethasone could be demonstrated, but after glutamine administration the stimulatory action of T3 was masked. T3 even increases fractional amino acid excretion in glutamine loaded rats as a sign of enhanced house-keeping in the renal tubular cells. These results confirm previous findings and indicate different effects of both hormones on the renal handling of amino acids.     

Epidermal growth factor (EGF) increases the renal amino acid transport capacity in amino acid loaded rats

Summary In anaesthetized adult female rats, the influence of epidermal growth factor (EGF) on renal amino acid handling was investigated in glutamine, arginine (both 50 mg/100 g b. wt. per hour), or alanine (90 mg/ 100 g b. wt. per hour) loaded animals. Continuous infusions of the three amino acids were followed by an increase in the fractional excretion (FE) of the administered amino acids as well as of the other endogenous amino acids. Under load conditions (alanine, arginine or glutamine), EGF pretreatment (8g/100g b. wt. subcutaneously for 8 days, twice daily 8 a.m. and 4 p.m.) was followed by a stimulation of renal amino acid reabsorption. The increase in the fractional excretion of the administered amino acids was significantly lower than in non-EGF-treated rats. These changes in amino acid transport were connected with a significant reduction of GFR after EGF pretreatment (0.96 ± 0.10 vs. 0.62 ± 0.07 ml/min X 100 g b. wt.) and a distinct increase in sodium excretion (2.98 ± 0.55 vs. 4.97 ± 0.71val/100 g b. wt. X 20 min). After loading with p-aminohippurate (PAH; 200mg/100g b. wt.), PAH excretion in EGF rats was increased by about 20%, whereas urinary protein excretion was lower in EGF pretreated rats (control: 0.45 ± 0.04 vs. EGF: 0.18 ± 0.03 mg/ 100 g b. wt. X 20 min). The PAH load reduced amino acid reabsorption as a sign of overloading of renal tubular transport capacity, but in EGF pretreated animals the amino acid excretion was only slightly increased under these conditions. Furthermore, EGF pretreatment depressed normal kidney weight gain significantly (874 ± 18 vs. 775 ± 32mg/100g b. wt.). EGF can improve the renal tubular transport capacity, but, compared to well-known stimulators of renal transport like dexamethasone or tri-iodothyronine, its effect is only of a moderate degree.     

Renal handling of amino acids in 5/6-nephrectomized rats: Stimulation of renal amino acid reabsorption after treatment with triiodothyronine or dexamethasone under amino acid load

Summary In anaesthetized adult female rats, the renal amino acid handling was measured six days after 5/6 nephrectomy (5/6NX). The distinct rise in blood urea nitrogen as well as the significant reduction in urine flow and GFR indicate an impairment of kidney function. In principle, in 5/6NX rats amino acid plasma concentrations were comparable to those of control animals with two intact kidneys, whereas the fractional excretions (FE_AA) of most endogenous amino acids measured were significantly enhanced. After bolus injection of leucine or taurine (each 20 mg/100 g b.wt.) or glutamine (90 mg/ 100 g b.wt.), dissolved in 2m1 normal saline per 100 g b.wt., the FE_AA of both the amino acids administered and the endogenous amino acids increased as a sign of overloaded amino acid reabsorption capacity. This effect was more pronounced in 5/6NX rats than in controls. As early as one hour after amino acid load, plasma concentrations and FE_AA returned to baseline values of 5/6NX rats. A pretreatment with triiodothyronine (20,µg/100 g b.wt.) or dexamethasone (60 µg/100 g b.wt.), both given intraperitoneally once daily for 3 days, stimulated the renal amino acid transport capacity in 5/6NX rats: the increase in FE_AA after amino acid load was significantly lower compared to non-pretreatred animals. This stimulation could be shown for the bolus amino acids and the endogenous amino acids and was more distinct in 5/6NX rats than in controls with two intact kidneys.     

Renal amino acid transport in immature and adult rats during chromate and cisplatinum-induced nephrotoxicity

Summary. The effects of sodium dichromate (chromate; 1 mg/100 g b. wt. s.c.) and cisdiamminedichloroplatinum(II) (CP; 0.6 mg/100 g b. wt. i.p.) on renal amino acid excretion and plasma amino acid composition were investigated in 10- and 55-day-old anaesthetised rats. On the basis of diuresis experiments on conscious rats the mentioned doses and times (1^st day after chromate in both age groups and in 10-day-old rats after CP and 3^rd day after CP in adult rats) were found out to be optimal for the characterisation of amino acid transport after heavy metal poisoning. Interestingly, in conscious 10-day-old rats chromate nephrotoxicity is not detectable after 1 mg/100 g b. wt. whereas all of the other experimental groups showed nephrotoxic effects of chromate and CP in conscious rats. Urine volumes are lower, but not significantly, in anaesthetised immature rats, independently of the administered nephrotoxin. But GFR is significantly lower in 10-day-old rats, both in controls and after CP, whereas after chromate GFR is significantly reduced only in adult rats and age differences disappeared. In principle the renal fractional excretion (FE) of amino acids was distinctly higher in immature rats as a sign of lower amino acid reabsorption capacity. Nevertheless, the amino acid plasma concentrations were relatively high in immature rats. However, both chromate and CP did not distinctly influence amino acid plasma concentrations. But in both age groups the administration of chromate and CP significantly decreased amino acid reabsorption capacity (increase in FE) as a sign of nephrotoxicity, most pronounced in adult rats after CP. The investigation of renal amino acid handling confirms (1) that both CP and chromate are nephrotoxins, (2) that CP was more nephrotoxic in 55-day-old animals compared to immature rats as could be demonstrated before using other parameters for nephrotoxicity testing and showed (3) that determination of renal amino acid handling is a highly sensitive marker for nephrotoxicity testing, especially in immature rats. Received March 3, 2000 Accepted October 11, 2000     

Identification of the site of glucocorticoid action on neutral amino acid transport in superficial nephrons of rat kidney

Summary. Glucocorticoid hormones enhance the reabsorptive capacity of filtered amino acids in rat kidney, as it was shown in previous in vivo clearance experiments. In the present study, the site of glucocorticoid action on neutral amino acid transport in superficial nephrons of rat kidney was investigated using in vivo micropuncture technique. Adult female Wistar rats were treated with dexamethasone (DEX), and fractional excretion of L-glutamine (L-Gln) and L-leucine (L-Leu) were determined and related to inulin after microinfusion into different nephron segments. DEX reduced fractional excretion of both neutral amino acids as a sign of enhanced reabsorptive capacity. The site of main DEX action on L-Leu reabsorption has been localized in the proximal straight tubule. However, in the case of L-Gln, the inhibition of γ-glutamyltranspeptidase (γ-GT) by administration of acivicin indicated the importance of this brush border enzyme in reduced L-Gln excretion. DEX enhanced γ-GT activity by tubular acidification. It can be presumed a DEX-inducible transport system for neutral amino acids mainly localized in proximal straight tubules of rat kidney. Received July 8, 1999     

Renal amino acid excretion and aging

The urinary excretion and serum concentration of amino acids were studied in 62 healthy individuals aged 15 to 70 years. In elderly subjects (61-70 years), it was found that renal amino acid clearance per 100 ml GFR (fractional excretion, FE) rose significantly in the following amino acids: CYS, VAL, MET, ILE and LEU. Since the serum concentrations of these amino acids showed no significant changes, but the GFR was reduced, it can be concluded that the raised FE of these amino acids was due to a decrease in their effective tubular reabsorption. A significant correlation was found between FENa and FE of most amino acids including those mentioned above. The findings support the assumption that changes in tubular Na+ transport probably participate in the changes of tubular amino acid transport in elderly individuals.     

Effect of polyaspartic acid on CdCl2-induced nephrotoxicity in the rat

We produced an animal model of CdCl₂ nephrotoxicity in rats, and treated them with polyaspartic acid (PAA) to prevent renal damage. Male Sprague-Dawley (SD) rats (190–200 g) were used to induce proximal renal tubular damage by daily injection of CdCl₂ 3.0 mg/1,000 g body wt for 2 wk. CdCl₂-exposed SD rats exhibited significant increases in urine volume, urinary excretion ofN-acetyl-β-D-glucosaminidase (NAG), alanine aminopeptidase (AAP), and fractional excretion of sodium (FENa) and a decrease in the percentage of tubular reabsorption of phosphate (%TRP). Of these indicators of proximal tubular function, AAP and %TRP are more sensitive than NAG or FENa. No glycosuria or aminoaciduria, however, were observed. PAA markedly improved these indicators of proximal tubular function. Daily urinary protein excretion and creatinine clearance, on the other hand, did not change after administration of PAA. Cd concentrations in the cortex were 3 times higher than in the medulla, however, there were no differences between Cd-treated rats and PAA-treated rats. Our animal model is an excellent one for determining the effect of cadmium on renal proximal tubule damage. PAA appears to be useful in the treatment of CdCl₂ nephrotoxicity.     

Zea mays L. extracts modify glomerular function and potassium urinary excretion in conscious rats

Diuretic and uricosuric properties have traditionally been attributed to corn silk, stigma/style of Zea mays L. Although the diuretic effect was confirmed, studies of the plant's effects on renal function or solute excretion were lacking. Thus, we studied the effects of corn silk aqueous extract on the urinary excretion of water, Na+, K+, and uric acid. Glomerular and proximal tubular function and Na+ tubular handling were also studied. Conscious, unrestrained adult male rats were housed in individual metabolic cages (IMC) with continuous urine collection for 5 and 3 h, following two protocols. The effects of 25, 50, 200, 350, and 500 mg/kg body wt. corn silk extract on urine volume plus Na+ and K+ excretions were studied in water-loaded conscious rats (2.5 ml/100 g body wt.) in the IMC for 5 h (Protocol 1). Kaliuresis was observed with doses of 350 (100.42 +/- 22.32-120.28 +/- 19.70 microEq/5 h/100 g body wt.; n = 13) and 500 mg/kg body wt. (94.97+/- 29.30-134.32 +/- 39.98 microEq/5h/100 g body wt.; n = 12; p<0.01), and the latter dose resulted in diuresis as well (1.98 +/- 0.44-2.41 +/- 0.41 ml/5 h/100 g body wt.; n = 12; p<0.05). The effects of a 500 mg/kg body wt. dose of corn silk extract on urine volume, Na+, K+ and uric acid excretions, and glomerular and proximal tubular function, were measured respectively by creatinine (Cler) and Li+ (ClLi) clearances and Na+ tubular handling, in water-loaded rats (5 ml/100 g body wt.) in the IMC for 3 h (Protocol 2). Clcr (294.6 +/- 73.2, n = 12, to 241.7 +/- 48.0 microl/ min/100 g body wt.; n = 13; p<0.05) and the Na+ filtered load (41.9 +/- 10.3, n = 12, to 34.3 +/- .8, n = 13, p<0.05) decreased and ClLi and Na+ excretion were unchanged, while K+ excretion (0.1044 +/- 0.0458, n=12, to 0.2289 +/- 0.0583 microEq/min/100 body wt.; n = 13; p<0.001) increased. For Na+ tubular handling, the fractional proximal tubular reabsorption (91.5 +/- 3.5, n = 12, to 87.5 +/- 3.4%; n = 13; p<0.01) decreased, and both fractional distal reabsorptions--I and II--increased (96.5 +/- 1.5, n = 12, to 97.8 +/- 0.9%; n = 13; p<0.01; and 8.2 +/- 3.5, n = 12, to 12.2 +/- 3.4%, n = 13, p<0.01, respectively). To summarize, in water-loaded conscious rats (2.5 ml/100 body wt.), corn silk aqueous extract is diuretic at a dose of 500 mg/kg body wt. and kaliuretic at doses of 350 and 500 mg/kg body wt. In water-loaded conscious rats (5.0 ml/100 g body wt.), corn silk aqueous extract is kaliuretic at a dose of 500 mg/kg body wt., but glomerular filtration and filtered load decrease without affecting proximal tubular function, Na+, or uric acid excretion.     

Analysis of trace amino acid neurotransmitters in hypothalamus of rats after exhausting exercise using microdialysis

A simple but effective coupling of microdialysis and capillary electrophoresis with laser induced fluorescence detection technique was applied to analysis of amino acid neurotransmitters in the hypothalamus of rats after acute exhausting exercise. The separation of amino acids was achieved using an uncoated fused-silica capillary (57 cm×75 μm I.D.) with a buffer of 10 mM disodium tetraborate at pH 10 and an applied voltage of 12.5 kV. The detection limit was 10⁻¹⁰ M for each amino acid. It is sufficiently sensitive and rapid for the determination of amino acids in a 5-μl Microdialysate. In comparison to pre-exercise, a significant increase in the levels of six hypothalamic amino acids (arginine, glycine, lysine, glutamic acid, alanine, γ-amino-n-butyric acid) was found after exercise. These results demonstrate that the increase of metabolic amino acids in the hypothalamus of rats can be induced by exhausting exercise and suggests that amino acid neurotransmitters may play functional roles in the central effects of exercise.     

Plasma levels and renal handling of endogenous amino acids in snakes: a comparative study

Plasma levels of 22 endogenous amino acids were measured by ion-exchange chromatography in four species of snakes: Thamnophis sirtalis, T. radix, Aipysurus laevis, and Python molurus. Despite considerable interspecific variation in the amino acid composition, all species showed relatively high plasma concentrations of histidine, a feature apparently unique to reptiles. The renal handling of these amino acids was studied by renal clearance methods. As in other vertebrates, net tubular absorption of filtered amino acids predominated. However, net tubular secretion of taurine, cysteic acid and/or phosphoserine and beta-alanine was observed, with taurine being the predominant amino acid secreted. The percentage reabsorption of the total amino acids filtered by the snake kidneys ranged from 79 to 95%. Evidence for the postrenal absorption of amino acids in these reptiles is presented. In species that normally undergo hibernation (Thamnophis spp.), the ability of the kidney to reabsorb amino acids was depressed by cold acclimation. Cold acclimation significantly decreased plasma levels of all amino acids except taurine, whose concentration increased. The increase in plasma taurine level may have resulted from cellular osmoregulation. Under these conditions, renal excretion of taurine increased concomitantly with the increase in plasma taurine concentration.     

Branched chain amino acid aminotransferase isoenzymes of Pseudomonas cepacia

Pseudomonas cepacia grew rapidly using a mixture of all three branched chain amino acids as carbon source, but failed to use individual branched chain amino acids as sole carbon source. Extracts of bacteria grown on branched chain amino acids had between 2- and 3-fold higher levels of -ketoglutarate-dependent branched chain amino acid aminotransferase activity than extracts of glucose-grown bacteria. The increase in enzyme activity was due to the presence of a second aminotransferase not detected in extracts of glucose-grown bacteria. The enzyme, which presumably plays a role in branched chain amino acid degradation, had an apparent molecular weight (mol. wt.) of 75,000. The other aminotransferase was formed constitutively and apparently functions in synthesis of branched chain amino acids. It was more stable than the 75,000 mol.wt. enzyme, and was purified to homogeneity and found to be a 180,000 mol.wt. oligomer containing 6 subunits of approximately 30,000 mol.wt. Antiserum prepared against the purified enzyme inhibited its activity but failed to influence the activity of the 75,000 mol.wt. aminotransferase, suggesting that the two isoenzymes are encoded by different genes.     

Metabolic costs of amino acid and protein production in Escherichia coli

Escherichia coli is the most popular microorganism for the production of recombinant proteins and is gaining increasing importance for the production of low-molecular weight compounds such as amino acids. The metabolic cost associated with the production of amino acids and (recombinant) proteins from glucose, glycerol and acetate was determined using three different computational techniques to identify those amino acids that put the highest burden on the biosynthetic machinery of E. coli. Comparing the costs of individual amino acids, we find that methionine is the most expensive amino acid in terms of consumed mol of ATP per molecule produced, while leucine is the most expensive amino acid when taking into account the cellular abundances of amino acids. Moreover, we show that the biosynthesis of a large number of amino acids from glucose and particularly from glycerol provides a surplus of energy, which can be used to balance the high energetic cost of amino acid polymerization.     

The amino acid permease AAP8 is important for early seed development in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

The development of seeds depends on the import of carbohydrates and amino acids supplied by the maternal tissue via the phloem. Several amino acid transporters have been reported to be expressed during seed and silique development in Arabidopsis thaliana (L.) Heynh. Here we show that mutants lacking the high affinity amino acid permease 8 (At1g10010) display a severe seed phenotype. The overall number of seeds and the number of normally developed seed is reduced by ∼50% in siliques of the Ataap8 T-DNA insertion mutant. This result could be reproduced in plants where expression of AtAAP8 is targeted with an RNAi approach. The seed phenotype is correlated with a specifically altered amino acid composition of young siliques. Aspartic acid and glutamic acid are significantly reduced in young siliques of the mutants. In correlation with the fact that AAP8 is a high affinity transporter for acidic amino acids, translocation of ¹⁴C-labelled aspartate fed via the root system to seeds of the mutants is reduced. AAP8 plays a crucial role for the uptake of amino acids into the endosperm and supplying the developing embryo with amino acids during early embryogenesis.     

Differential coupling efficiency of chemically activated amino acid to tRNA

Summary Interaction based on possible chemical affinity of an amino acid for tRNA was examined as a model for the aminoacylation of primitive tRNA without aid of an enzyme system. Two types of reaction were carried out and compared. One was the acyl linkage of amino acid to the 5-terminal phosphate of a tRNA activated as an imidazolide. The other was the incorporation of an amino acid activated as an imidazolide into 2(3)-hydroxyl groups of intact tRNA. Both types of reaction indicated that none of the amino acids tested had any selectivity for the tRNAs examined. However, the rates of reaction with a given tRNA were different among amino acids. In the second type of reaction, amino acids were found mainly at loop-out regions of tRNA, but not at either its 5- or 3-terminal sitesOneA ₂₆₀ unit is defined as an amount of material which gives an absorption of 1.0 at 260 nm when dissolved in 1 ml water and measured with a 1-cm light path     

Biliary amino acid excretion in rats before and after bilateral nephrectomy.

In previous studies it could be shown that after bilateral nephrectomy (NX) the excretory function of the liver is disturbed. To further clarify whether or not this "renohepatic syndrome" is caused by toxic effects of uremia or by competition phenomena between various uraemic toxins an additional aspect was investigated: the biliary excretion of endogenous amino acids. Furthermore, previously it could be shown that renal and hepatic excretory functions overlap. Therefore, the renal excretion of effectively biliary eliminated amino acids (glutamic acid, alanine, tyrosine, isoleucine) is very low and vice versa. That means, that the renal excretion of amino acids with low hepatic elimination (tryptophan, citrulline, lysine, taurine) dominates. The hepatic excretion of amino acids is hardly altered after NX. Remarkably, the removal of both kidneys is followed by a distinct reduction in amino acid plasma concentrations, especially if these concentrations are relatively high in the controls. Interestingly, there is no correlation between plasma concentrations and biliary excretion of amino acids. But the calculation of the bile to plasma concentration ratios of amino acids makes it possible to differentiate three groups of amino acids: Amino acids excreted actively into bile (ratio > or = 1), amino acids with ratios below 1, indicating effective retention, and amino acids with ratios of about 1, whose hepatic handling is passive. After NX these ratios tended to approach 1; low ratios increased and high ratios decreased. That means, active processes involved in excretion or retention are obviously disturbed. These changes could indicate uraemic liver damage as proved regarding influence of NX on hepatic excretion of other endogenous substances and xenobiotics.     

Chloroquine,a novel inhibitor of amino acid transport by rat renal brush border membrane vesicles

Summary Chloroquine is an antimalarial and antirheumatic lysosomotropic drug which inhibits taurine uptake into and increases efflux from cultured human lymphoblastoid cells. It inhibits taurine uptake by rat lung slices and affects the uptake and release of cystine from cystinotic fibroblasts. Speculations on its mode of action include a proton gradient effect, a non-specific alteration in membrane integrity, and membrane stabilization. In this study, the effect of chloroquine on the uptake of several amino acids by rat renal brush border membrane vesicles (BBMV) was examined. Chloroquine significantly inhibited the secondary active, NaCl-dependent component of 10µM taurine uptake at all concentrations tested, but did not change equilibrium values. Analysis of these data indicated that the inhibition was non-competitive. Taurine uptake was reduced at all osmolarities tested, but inhibition was greatest at the lowest osmolarity. Taurine efflux was not affected by chloroquine, nor was the NaCl-independent diffusional component of taurine transport. Chloroquine (1 mM) inhibited uptake of the imino acids L-proline and glycine, and the dibasic amino acid L-lysine. It inhibited the uptake of D-glucose, but not the neutral-amino acids L-alanine or L-methionine. Uptake of the dicarboxylic amino acids, L-glutamic acid and L-aspartic acid, was slightly enhanced. With regard to amino acid uptake by BBMV, these findings may support some of the currently proposed mechanisms of the action of chloroquine but further studies are indicated to determine why it affects the initial rate of active amino acid transport.     

Evolutionary changes reflected by the cellular amino acid composition

Summary Comparison of the amino acid composition of cell-proteins using 17 amino acids has been used to investigate the biological evolution of organisms such as bacteria, blue-green alga, green alga, fungi, slime mold, protozoa and vertebrates. The degree of difference in the amino acid ratios between any two groups reflects the degree of divergency in biological evolution. The amino acid composition of the Gram-negative bacteria (Escherichia coli,Klebsiella,Proteus, andVibrio alginolyticus) was identical. However, the amino acid composition ofStaphylococcus aureus andBacillus subtilis, which are Gram-positive bacteria, differed from each other and from the Gram-negative bacteria. The amino acid composition of the blue-green alga (Cyanobacterium,Chroococidiopsis) was quite similar to that ofE. coli. A marked difference in the amino acid composition was observed betweenE. coli and green alga (Chlorella), and significant differences were observed betweenE. coli and other organisms, such as fungi, protozoa (Tetrahymena), slime mold (Dictyostelium discoideum) and vertebrates. In conclusion, the change in cellular amino acid composition reflects the divergence which has occurred during biological evolution, whereas a basic pattern of amino acid composition is maintained in spite of a long period of evolutional divergence among the various organisms. Thus, it is proposed that the primitive life forms established at the end of prebiotic evolution had a similar amino acid composition.     

Regulation of amino acid transport in growing cells of Streptomyces hydrogenans

(1) The active uptake of different amino acids by growing cells of Streptomyces hydrogenans was shown to be correlated with the physiological age of the cells. During the lag phase of growth the transport capacity increased and attained its highest level when the growth rate was maximum. During further growth the transport capacity declined progressively. The lowest transport activity was observed when the culture shifted into the stationary growth phase. (2) Such modulation of transport capacity was independent on the presence or absence of amino acids in the growth medium of the cells. (3) The size and the composition of the pool of free intracellular amino acids was also undergoing substantial variations during the growth cycle of the culture. In the lag phase, the levels of all amino acids decreased markedly and attained their lowest values at the end of this phase. During further growth the pool size was slowly replenished. (4) Removal of the pool resulted in a considerable gain of transport capacity. Therefore, it was concluded that active amino acid transport in growing Streptomyces hydrogenans is under feedback control by intracellular amino acids. (5) Quantitatively, the modulation of the pool size could not fully account for the variation of the transport capacity. Since a pool-independent stimulation of transport was found to be correlated with the increase of the growth rate of the cells, the possibility is discussed that the stimulation of transport is either due to increased levels of distinct RNA species, which might provide positive feedback signals for transport, or by increased rates of de novo synthesis of transport limiting proteins.List of Abbreviations AIB 2-aminoisobutyric acid - CM complete medium - MM mineral medium     

Submerged culture conidial germination and conidiation of the bioherbicideColletotrichum truncatum are influenced by the amino acid composition of the medium

Summary Submerged culture experiments were conducted to determine the optimal nitrogen source for rapidly producing conidia of the bioherbicide,Colletotrichum truncatum. Germination ofC. truncatum conidial inocula in submerged culture occurred most rapidly (>95% in 6 h) in media provided with a complete complement of amino acids. When (NH₄)₂SO₄, urea, or individual amino acids were provided as the sole nitrogen source, conidial germination was less than 20% after 6 h incubation. Conidia production was delayed inC. truncatum cultures grown in media with urea or individual amino acids as nitrogen sources compared to cultures supplied with Casamino acids or complete synthetic amino acid nitrogen sources. The use of methionine, lysine, tryptophan, isoleucine, leucine or cysteine as a sole nitrogen source severely inhibitedC. truncatum conidia production. Media with synthetic amino acid mixtures less these inhibitory amino acids produced significantly higher conidia yields compared to media with amino acid mixtures containing these amino acids. When various amounts of each individual inhibitory amino acid were added to media which contained amino acid mixtures, cysteine and methionine were shown to be most effective in reducing conidiation. An optimal nitrogen source forC. truncatum conidiation in submerged culture should contain a complete mixture of amino acids with low levels of cysteine, methionine, leucine, isoleucine, lysine and tryptophan for rapid conidiation and optimal conidia yield.The mention of firm names or trade products does not imply that they are endorsed or recommended by the US Department of Agriculture over other firms or similar products not mentioned.     

Regulation of renal amino acid (AA) transport by hormones,drugs and xenobiotics – a review

Major advances have recently been made in our understanding of the mechanisms and functions of amino acid transport in mammalian cells: - from the whole organism to transporter molecular structure. In this article, we present a brief overview of current knowledge concerning amino acid transporters, followed by a detailed discussion of the relevance of this new information to our broader understanding of the physiological regulation of amino acid handling in the kidney. We focus especially on the influence of hormones and xenobiotics on renal amino acid transport systems. In a growing number of cases, it now seems possible to correlate the effects of hormones, drugs, and xenobiotics with the capacity of renal amino acid transporters. This topic is of clinical relevance for the treatment of many amino acid reabsorption disorders. For example, under suitable conditions glucocorticoids and thyroid hormones stimulate renal reabsorption of amino acids and might therefore be of benefit in the treatment of different kinds of aminoaciduria. Hormonal regulation also underlies the postnatal development of renal amino acid reabsorption capacity, which can be stimulated to mature earlier after exogenous administration of e.g. glucocorticoids. In contrast, many compounds (e.g. heavy metal complexes) selectively damage renal amino acid transporters resulting in urinary amino acid loss. These types of phenomena (stimulation or inhibition of amino acid transporters in the kidney) are reviewed from the perspectives of our new molecular understanding of transport processes and of clinical relevance.