Cloning and characterization of rat cysteine sulfinic acid decarboxylase.

Cysteine sulfinic acid decarboxylase (CSAD) is a key enzyme in taurine biosynthesis. CSAD activity and enzyme protein concentration are both repressed by the action of the steroid family hormones triiodothyronine and estrogen. To characterize this suppression, a cDNA clone for CSAD was isolated from a rat liver cDNA expression library using polyclonal antibodies to CSAD. The cDNA was sequenced in its entirety and confirmed to be a clone of CSAD. In a Northern blot comparing liver and kidney RNA of male and female rats, the CSAD cDNA probe detected a 2.5 kb mRNA band which was present at levels corresponding to the concentration of enzyme protein. Hyperthyroidism decreased CSAD mRNA as compared to euthyroid controls, providing evidence that negative regulation of CSAD activity occurs at the level of mRNA.

Computer-based visual communication in aphasia.

The authors describe their recently developed Computer-aided VIsual Communication (C-VIC) system, and report results of single-subject experimental designs probing its use with five chronic, severely impaired aphasic individuals. Studies replicate earlier results obtained with a non-computerized system, demonstrate patient competence with the computer implementation, extend the system's utility, and identify promising areas of application. Results of the single-subject experimental designs clarify patients' learning, generalization, and retention patterns, and highlight areas of performance difficulties. Future directions for the project are indicated.

13-cis-retinoic acid and hepatic steatosis in rats.

The effect of administration of 13-cis-retinoic acid (100 mg/kg diet) on lipid metabolism was examined in male rats fed either a 20% casein + 0.3% methionine diet, a 20% casein diet, a 10% casein + 0.3% methionine diet, or a 10% casein + 0.6% methionine diet for 10 days. Hepatic triglyceride concentrations of rats fed either 10% casein diet were 3-fold greater than animals receiving diets containing 20% casein. The addition of 13-cis-retinoic acid to the diet further increased the total hepatic lipid (43-56%) and triglyceride (approximately 2-fold) concentrations in rats fed the 10% casein diets. 13-cis-Retinoic acid supplementation did not alter the total liver lipid or triglyceride concentrations in rats fed either of the 20% casein diets. Thus, under specific dietary conditions, the administration of 13-cis-retinoic acid resulted in a marked accumulation of hepatic lipids which did not appear to be related to the total methionine content of the diet nor to the hepatic concentrations of S-adenosylmethionine and glutathione. In addition, all four groups of 13-cis-retinoic acid-fed rats exhibited elevations in the concentration of serum triglycerides, and 10-20% reductions in serum cholesterol concentrations.

Transaminative metabolism of alpha-amino-n-butyrate in rats.

alpha-Amino-n-butyrate metabolism was studied in a rt tissue homogenate system using L-[1-14C] alpha-amino-n-butyrate. Transamination was found to be the major route in the liver for the metabolism of L-alpha-amino-n-butyrate based on 44.8 mumoles/g/h of [1-14-C] alpha-ketobutyrate formed in the presence of pyruvate versus 1.2 mumoles/g/h without pyruvate. The pH optimum for the reaction was 9.2. The abilities of other alpha-keto acids to act as a cosubstrate relative to pyruvate were (%): pyruvate, 100; alpha-ketobutyrate, 80; alpha-keto-gamma-methiolbutyrate, 15; phenylpyruvate, 14; alpha-ketoglutarate, p-hydroxyphenylpyruvate and the alpha-keto analogs of the branched-chain amino acids, all less than 10. The apparent Km for alpha-amino-n-butyrate in the liver homogenate was approximately 38 mM and the Km for pyruvate was 5 mM. Kidney was found to have about twice the activity as liver. Activities in brain, heart, diaphragm, muscle and small intestine were negligible. With the exception of serine, no other added amino acids could compete effectively with alpha-amino-n-butyrate for transamination in the rat liver homogenate system. Activity in rat liver was inhibited by aminooxyacetic acid and cycloserine. These results indicate that alpha-amino-n-butyrate is metabolized primarily by a transaminase reaction with pyruvate which occurs almost exclusively in liver and kidney.

Modification of hepatic folate metabolism in rats fed excess retinol.

Feeding rats a diet containing 1000 IU of retinol/g diet enhances the folate-dependent oxidation to CO2 of formate and histidine. The activity of hepatic methylenetetrahydrofolate reductase, which plays a critical role in the regulation of liver folate metabolism, is suppressed in these animals, resulting in decreased 5-methyltetrahydrofolate synthesis. This ensures a greater concentration of hepatic tetrahydrofolate, the coenzyme on which formate and histidine oxidation depend, but also compromises the level of S-adenosylmethionine in the liver.

Processing of visual syntax in a globally aphasic patient.

A globally aphasic patient was trained on a computerized visual communication system. His ability to comprehend reversible locative prepositional phrases after training was studied and compared with the performance of Broca's aphasics on a similar task. This patient's ability to generalize symbols for actions was also investigated. The results demonstrate our patient's capacity to master a formal visual syntax in the absence of natural language and illustrate how this capacity may be used successfully in a visual communication system. A problem in generalizing symbols for actions is demonstrated, suggesting that certain heuristic and cueing capabilities in the approach may be helpful.

Variations in S-adenosylmethionine, S-adenosylhomocysteine and adenosine concentrations in rat liver.

The hepatic concentrations of S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH) and adenosine (Ado) in the rat were examined diurnally and as a function of fasting. Ado concentrations increased continuously throughout the fasting period; concentrations after 2 days of fasting were 7.5-fold higher than control values. Diurnally, the concentration of Ado was highest during the light hours. SAM and the ratio of SAM/SAH were reduced greater than 50% due to fasting and exhibited a significant daily rhythm which appeared to be related to dietary methionine availability. Hepatic SAM concentrations decreased continuously during the light hours and increased during the dark period to levels 7.3-fold greater than the lowest light values. The concentration of SAH was altered in a similar fashion yet to a much lesser degree such that the ratio of SAM/SAH paralleled the changes in the concentration of SAM. The SAM/SAH ratio exhibited a 4.5-fold difference between the peak and nadir values.

A torted pelvic spleen.

An unusual case of an acute abdomen due to a torted wandering spleen in the pelvis is presented. As is usual for the few cases reported, the diagnosis was unsuspected pre-operatively. The treatment is splenectomy and a quick and complete recovery followed this. Literature on the subject is reviewed.

Blood-brain barrier transport of the alpha-keto acid analogs of amino acids.

A number of alpha-keto acid analogs of amino acids have been found to penetrate the blood-brain barrier (BBB). Pyruvate, alpha-ketobutyrate, alpha-ketoisocaproate, and alpha-keto-gamma-methiolbutyrate all cross the BBB by a carrier-mediated process and by simple diffusion. Under normal physiological conditions, diffusion accounts for roughly 15% or less of total transport. Aromatic alpha-keto acids, phenylpyruvate, and p-hydroxyphenylpyruvate do not penetrate the BBB, nor do they inhibit the transport of other alpha-keto acids. Evidence based primarily on inhibition studies indicates that the carrier-mediated transport of alpha-keto acids occurs via the same carrier demonstrated previously for propionate, acetoacetate, and beta-hydroxybutyrate transport, commonly referred to as the monocarboxylate carrier. As a group, the alpha-keto acid analogs of the amino acids have the highest affinity for the carrier, followed by propionate and beta-hydroxybutyrate. Starvation for 4 days induces transport of alpha-keto acids, but transport is suppressed in rats fed commercial laboratory rations and subjected to portacaval shunts. The mitochondrial pyruvate translocator inhibitor alpha-cyanocinnamate has no effect on the BBB transport of alpha-keto acids.

Hyperammonemia and orotic aciduria in portacaval-shunted rats.

The effect of a portacaval shunt-induced alteration in liver function on nitrogen metabolism was studied in rats. Within a few days after surgery, portacaval-shunted rats grew with an average daily gain in body weight equal to sham-operated control rats. Within 1 week after surgery, portacaval-shunted rats excreted 20% more orotic acid in their urine compared to control rats. The difference increased to 37% after 3 weeks. Plasma ammonia levels were elevated by 78% in portacaval-shunted rats compared to control rats after 2 weeks. Portacaval-shunted rats injected with a challenging load of ammonium chloride (5 mmol/kg) excreted half as much orotic acid in their urine over a 24-hour period as similarly injected controls. The simultaneous injection of 1.5 mmol/kg of arginine prevented the ammonia-induced increase in orotic acid excretion in both shunted and control rats. However, feeding rats diets supplemented with 1% arginine did not prevent the chronic hyperammonemia and orotic aciduria produced by the construction of portacaval shunts. Similar experiments with diets supplemented with 1% sodium benzoate to induce alternative pathways for nitrogen excretion were also without effect. These results are in contrast to recent clinical studies reporting the effectiveness of sodium benzoate in treating hyperammonemia in patients with urea cycle enzyme defects.

Role of 3-ethylthiopropionate in ethionine metabolism and toxicity in rats.

The potential role of the pathway for ethionine catabolism involving the intermediate formation of 3-ethylthiopropionate in the etiology of ethionine hepatotoxicity was studied in rats. Rats were fed diets containing graded levels of 3-ethyl-thiopropionate, an intermediate of this pathway, for three weeks. A dietary level as low as 0.4% was toxic to rats, resulting in depressed growth and food intake, decreased blood hemoglobin levels and darkened and enlarged spleens. All animals fed 3-ethylthiopropionate expired a volatile sulfur compound that was identified as ethanethiol by gas chromatography using both a general flame ionization detector and a sulfur specific flame photometric detector. Rats fed diets containing either 0.8% ethionine or 3-ethylthiopropionate exhibited an 80% decrease in body weight gain over a three-week period compared to controls. Spleens were markedly darkened and enlarged and spleen iron content was 6-fold and 1.5-fold higher than controls in 3-ethylthiopropionate-fed and ethionine-fed rats, respectively. Liver concentrations of reduced and total glutathione were 30% higher than controls in ethionine-fed rats. There results document the marked toxicity of 3-ethylthiopropionate and ethionine and suggest that this pathway for ethionine catabolism may be involved in some of the numerous reported metabolic aberrations as a result of acute or chronic ingestion of ethionine.

13-cis-retinoic acid alters methionine metabolism in rats.

The effect of dietary 13-cis-retinoic acid (CRA) on hepatic methionine metabolism was examined in young male rats. Rats were fed a 10% casein diet (controls) or this diet supplemented with L-methionine (10 g/kg diet), with or without the addition of CRA (100 mg/kg diet), for 10 d. Methionine-supplemented rats exhibited 7.3- and 1.7-fold greater concentrations of hepatic S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH), respectively, relative to controls, which resulted in a 4.9-fold greater SAM:SAH ratio. Likewise, hepatic methionine and taurine concentrations were 6.9- and 4.3-fold greater, respectively, in methionine-supplemented rats than in controls. The addition of CRA to the methionine-supplemented diet prevented the elevations in the hepatic methionine concentration and the SAM:SAH ratio, whereas taurine levels were greater than in methionine-supplemented rats. In rats pretreated with the methionine-supplemented diet, a reduction in the SAM:SAH ratio occurred within 2 d following the addition of CRA to the methionine-supplemented diet. Rats receiving the methionine-supplemented diet exhibited 9.2- and 3.7-fold greater urinary taurine and inorganic sulfate excretions, respectively, relative to controls. Addition of CRA to the methionine-supplemented diet significantly reduced sulfate excretion by 21%. These findings indicate that dietary CRA has the ability to alter the catabolism of methionine and subsequently influence hepatic transmethylation as reflected by the SAM:SAH ratio.

Dietary sulfur amino acid modulation of cysteine sulfinic acid decarboxylase.

Male rats were fed sulfur and nonsulfur amino acid-supplemented diets, and the response of cysteine sulfinic acid decarboxylase (CSAD) activity was determined. After adaptation to a casein-based basal diet, rats were fed diets containing additions of L-methionine. Hepatic CSAD activity decreased in a dose-dependent manner. Significant depression of CSAD activity in liver was evident within 24 h of feeding rats a methionine-supplemented diet. Depression of enzyme activity was reversed upon refeeding the basal diet. After rats were fed diets supplemented with methionine, cystine, homocystine, S-methyl-L-cysteine, phenylalanine, leucine, or ethionine for 14 days, hepatic CSAD activity in rats fed S-methyl-L-cysteine-, phenylalanine-, or leucine-supplemented diets was not depressed compared with activity in rats fed a basal diet. In contrast, CSAD activity in livers of rats fed cystine-, homocystine-, methionine-, or ethionine-supplemented diets was 60, 40, 40, and 8%, respectively, of the activity in livers from control rats. Immunochemical detection and quantification of CSAD protein in rat liver indicated that CSAD protein concentration was correlated to CSAD activity. CSAD activity may be specifically regulated by sulfur amino acids metabolized by the S-adenosylmethionine-dependent pathway of methionine metabolism.

Cysteine sulfinic acid decarboxylase activity in response to thyroid hormone administration in rats.

The modulation of hepatic and renal cysteine sulfinic acid decarboxylase (EC 4.1.1.29) activities by triiodothyronine (T3) was studied in a series of experiments. In a dose--response study, hepatic cysteine sulfinic acid decarboxylase activity (CSAD) was depressed by 65% and renal activity was increased threefold in rats injected with 100 micrograms T3/100 g body wt for 7 days when compared to rats injected with 0.3 micrograms T3/100 g body wt. Western blot analysis indicated that these changes in CSAD activity were due to changes in the quantity of CSAD protein. Changes in hepatic and renal activities were not evident until 24 h after T3 administration. In response to T3 clearance, hepatic and renal CSAD activities approached euthyroid values 4-7 days after cessation of T3 injections although serum T3 concentrations were no different from euthyroid values 48 h after T3 injections were stopped. These data indicate that thyroid hormone effects persist after T3 clearance. The response of CSAD to thyroid status may be related to its role in taurine biosynthesis.

Diet composition and surgical technique influence the postoperative recovery of portacaval shunted rats.

In a series of experiments, rats were subjected to end-to-side portacaval shunts using either suture or nonsuture surgical procedures. Rats were maintained on cereal-based or purified diets in pellet form. All rats recovered preoperative body weights within the experimental periods; however, recovery of preoperative body weight was influenced by surgical technique and diet composition. Portacaval shunted rats fed a cereal-based diet required a longer period of time (14 days) to reattain preoperative body weights when compared to portacaval shunted rats fed a purified diet (7 days). Once preoperative body weight was recovered, growth rates of portacaval shunted rats were parallel to those of sham-operated controls. Rats with a suture-portacaval shunt appeared most sensitive to the feeding of a cereal-based diet. All portacaval shunted rats and sham controls fed a purified diet regained preoperative body weights within 7 days after surgery. Sham controls fed either a cereal-based or purified diet recovered preoperative body weights within an average of 4 days. Suture-portacaval shunted rats consuming a pellet form cereal-based diet showed a low feed efficiency which could be reversed by feeding a pellet form purified diet. Rats subjected to a nonsuture glue-portacaval shunt and fed a cereal-based diet showed 50% lower feed efficiencies than did glue-portacaval shunted rats fed a purified diet. Portacaval shunted rats decreased their consumption of cereal-based diets but not of purified diets postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of dietary protein on nitrogen and sulfur metabolism in portacaval-shunted rats.

The effect of varying the amount of protein in the diet on postoperative recovery, plasma ammonia, urinary orotic acid and metabolism of sulfur-containing amino acids was examined in rats with portacaval shunts (PCS). Food intake and weight gain were lower in both PCS and control rats fed a low (6%) casein diet unsupplemented with methionine compared with rats fed an adequate (18%) casein diet. PCS rats fed 60% casein ate slightly less and took longer to recover their preoperative body weight compared to 60% controls. Shunted rats were consistently hyperammonemic and orotic aciduric compared to controls. Increasing protein in the diet elevated plasma ammonia and urinary orotic acid in all rats to levels above those of the rats fed 18% casein, but the effect was greater in rats with PCS. After i.p. injection of L-[35S]methionine or L-[35S]cysteine, urinary 35S and [35S]sulfate excretion increased and [35S]taurine and total taurine excretion decreased in all rats fed 60% casein. These changes are consistent with our observation that hepatic activities of cysteine dioxygenase and cysteine sulfinate:alpha-ketoglutarate aminotransferase increased and that of cysteine sulfinate decarboxylase decreased in rats fed the high protein diet. The effect of dietary treatment on both urinary taurine excretion and decarboxylase activity was greater in PCS rats than in controls. Although PCS rats fed a high protein diet may have a decreased taurine-synthesizing capability compared to controls, their ability to oxidize a methionine or cysteine load to sulfate is not compromised by feeding either an 18 or 60% casein diet.

Quantification of cysteine sulfinic acid decarboxylase in male and female rats: effect of adrenalectomy and methionine.

Hepatic cysteine sulfinic acid decarboxylase (EC 4.1.1.29) activity has been reported to decrease in response to both L-methionine (Met) feeding and adrenalectomy in rats. A series of experiments was conducted to (a) determine if CSAD depression was evident in female rats fed a methionine-supplemented diet; and (b) determine if adrenal hormones mediated the response of CSAD to dietary methionine. Cysteine sulfinic acid decarboxylase (CSAD) activity was measured in livers of male and female rats fed a methionine-supplemented diet. In female rat liver, CSAD activity was only 25% of the activity measured in livers of male rats. Hepatic enzyme activity in male rats fed a casein-based basal diet containing 0.6% L-methionine was 2.5-fold higher than activity in male rats fed a methionine-supplemented diet containing 1.35% L-methionine (+Met). Similarly, enzyme activity in livers of female rats fed the basal diet was 1.7-fold higher than in female rats fed a methionine-supplemented diet. CSAD activity in adrenalectomized (ADX) male rats fed the basal diet was depressed (990 +/- 120 nmol/min.g liver) compared to activity in intact controls (2347 +/- 89) and sham controls (2040 +/- 143) fed the basal diet. CSAD activity was further depressed in ADX, intact controls, and sham controls fed +Met. Immunochemical detection and quantification of CSAD protein in rat liver demonstrated that changes in CSAD protein were consistent with the observed decreased enzyme activity in female rats, ADX rats, and rats fed +Met. S-Adenosylmethionine and S-adenosylhomocysteine concentrations tended to increase in livers of rats fed +Met. ADX rats fed +Met had the greatest increase in S-adenosylmethionine and S-adenosylhomocysteine concentrations. The depression in hepatic CSAD observed after feeding +Met to rats does not appear to involve adrenal function.