Brain cortical amino acids measured by intracerebral dialysis in portacaval shunted rats

The extracellular amino acid content was measured in the parietal cortex in portacaval and sham operated rats, using the brain dialysis technique. The amino acid content of the perfusate was determined for 10 min before and during stimulation with potassium chloride. Basal levels of aspartate, glutamine, glycine, methionie, valine, phenylalanine and leucine were 2-to 6-fold higher in the PC-shunted as compared to the sham operated rats. For glutamate, taurine, and GABA no differences were observed between the two groups. After KCl stimulation the release of glutamate and GABA increased significantly in both groups. For GABA this rise was approximately twice as high in the PC-shunted rats (+300%,P<0.01) as in the sham operated rats (+150%,P<0.01 as compared to basal). In the sham operated, but not in the PC-shunted rats, methionine and valine levels rose significantly (+200%,P<0.05) and glutamine release decreased (–50%,P<0.05). These findings suggest that the brain metabolism of amino acids is altered after a portacaval shunt. This could in turn alter the neurotransmission and partly explain the low spontaneous motor activity seen in these animals.     

Effect ofl-dopa treatment on cerebral amino acid levels in rats after portocaval anastomosis

l-Dopa therapy has been suggested as effective in the reversal of hepatic coma both in humans and in animals. Beneficial effects have been reported also in chronic hepatic encephalopathy. There are many possible mechanisms through whichl-dopa could ameliorate this pathological state. The present study was carried out to clarify whether thel-dopa effect could be mediated through an improvement of the brain neutral amino acid patterns, since it competes for the same transport carrier at the blood-brain barrier. A first group of rats was orally administeredl-dopa (10 mg/100 g body weight daily) for 1 month following portocaval anastomosis. A second group was intraperitoneally injected (1.5 mg/100 g body weight daily) for 1 week, a month after portocaval shunt. Amino acid levels were determined in plasma and in four cerebral regions. No beneficial effects were observed clinically (in general condition, body weight, or hypertonic posture) in rats receivingl-dopa compared to controls. The large increase of tyrosine, phenylalanine, tryptophan, histidine, and glutamine that occurs in the cerebral tissue after portocaval shunt was also not affected byl-dopa administrations. In conclusion, in this experimental condition we had no clinical improvement in shunted animals receivingl-dopa. Moreover, this compound did not seem to influence the pathological increase of aromatic amino acids in the brain, which is considered to play an important role in hepatic encephalopathy.     

Effects of Dietary Amino Acids on Brain Amino Acids and Transmitter Amines in Rats with a Portacaval Shunt

The etiologic relationship between disturbances in metabolism of amino acids and amines and hepatic coma was investigated by examining the effects of diets containing various mixtures of amino acids on brain amine metabolism in rats with a portacaval shunt, using a method for simultaneous analysis of amino acids and amines. Rats with a portacaval shunt were fed on four different amino acid compositions with increased amounts of various amino acids suspected to be etiologically related to hepatic coma, such as methionine, phenylalanine, tyrosine, and tryptophan. The animals were killed 4 weeks after operation. During the experimental period, these animals did not become comatose, but exhibited various behavioral abnormalities. Marked increase in the plasma and brain levels of the augmented amino acids, especially methionine and tyrosine, were observed in rats with a portacaval shunt. Brain noradrenaline, dopamine, and serotonin levels were significantly decreased when the brain tyrosine level was increased. These results indicate that in rats with a portacaval shunt the dietary levels of amino acids greatly influence the brain levels of both amino acids and transmitter amines.     

Long-term effects of pinealectomy on the annual cycle of golden-mantled ground squirrels,Spermophilus lateralis

Summary Pinealectomies and radical sham pinealectomies were performed on adult golden-mantled ground squirrels (Spermophilus lateralis) approximately one month prior to the beginning of the normal winter hibernation season. The cyclic components of the overwintering period and subsequent active season (the rhythms of homeothermy-heterothermy, body mass and testicular function) of the first year were not disrupted in either of the operated groups as compared with the intact animals. In the second year, the initiation of the hibernatory period occurred as usual in all intact, pinealectomized, and sham operated animals, but the pinealectomized group failed to show the progressive increase in the length of heterothermic bouts that was characteristic of the intact and sham-pinealectomized squirrels. The loss of body mass also was accelerated in the pinealectomized squirrels with respect to the intact and sham groups and appeared to be associated with terminal arousal which occurred approximately six weeks earlier in the second year after pinealectomy. Additionally, male squirrels showed a correspondingly early onset of testicular development as compared to the intact and sham operated males.     

The Release and Neosynthesis of Glutamic Acid Are Increased in Experimental Models of Hepatic Encephalopathy

The effects of ammonium ions on the release of glutamic acid from the rat cerebral cortex were measured in vivo using cortical cups and a multiple ion detection technique. The neosynthesis of this amino acid from glucose was also studied in two experimental models of hepatic encephalopathy: (1) rats receiving large amounts of ammonium acetate (i.p.) and (2) rats with a surgically constructed portocaval anastomosis. Intraperitoneal administration of 8 mmol/kg of ammonium acetate increased the cortical release of glutamic acid from 9.1 +/- 0.8 to 19 +/- 2 (nmol X cm-2 X min-1). Moreover, 20 min after ammonium acetate administration the rate of incorporation of 13C2, originating from [13C]glucose, into glutamic acid increased by 65%. In several brain areas of rats bearing a portocaval anastomosis and fed ad libitum for 4 weeks, the content of glutamic acid slightly increased and the rate of formation of [13C2]glutamate from [13C]glucose approximately doubled. These results indicate that ammonium ions increase the release and the formation of glutamic acid in the brain. The resulting increased concentration of this amino acid in the extracellular spaces may be one of the mechanisms of ammonia toxicity in vivo.     

Metallothioneins in spontaneously hypertensive rat liver.

The metallothionein (MT) synthesis was induced in the liver of spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) rats through sc injections of CdCl2 for 3 and 6 days. The MT contents of the liver of these animals and of untreated rats from both groups were determined by gel filtration, HPLC, SDS/PAGE and amino acid analysis. The isoforms MT1 and MT2 were identified and their Cd, Zn and SH-group contents were determined. The SHR showed significantly higher values of MT than WKY rats in the untreated animals and on the 3rd day of the induction. On the 6th day, the MT levels in both groups were equal. The Cd and Zn contents followed the MT concentration in the homogenates. The possible relation between the arterial hypertension and the zinc and copper homeostasis is discussed.     

Sialic acid and neuraminidase activity in rat kidneys 6 months after uninephrectomy

Sialic acid and neuraminidase activity were determined in the cortex of the remnant kidneys of six uninephrectomized rats. As controls served either the kidneys removed at operation or age-matched kidneys from eight sham operated rats. Six months after uninephrectomy the kidneys became hypertrophied and their mean weight was about 40% higher than age-matched kidneys. Blood urea and creatinine and protein levels in 24-hr urine collections were significantly higher in the experimental animals as compared to those of the same animals before nephrectomy and to sham operated rats, indicating a marked impairment of kidney function. The mean concentration of sialic acid in the cortex of hypertrophied kidneys was not statistically different from either that of the removed or that of the age-matched kidneys. Neuraminidase activity expressed as either per gram fresh tissue or per milligram protein, was not different in the removed and in the hypertrophied kidney. The activity, however, in the latter was significantly lower than in the age-matched kidneys. Whether this finding can be associated with the impairment of kidney function in rats 6 months after uninephrectomy remains to be studied.     

Uptake of Amino Acids by Brain Micro vessels Isolated from Rats with Experimental Chronic Renal Failure

The neurological disorders seen in patients with chronic renal failure and liver cirrhosis are analogous. Previous in vivo studies have shown that the impaired blood-brain amino acid transport seen in rats with chronic renal failure is similar to that of rats with portocaval anastomosis. To elucidate whether a comparable underlying pathogenic mechanism plays a role in both pathological conditions, blood and brain amino acid levels together with amino acid transport by isolated brain microvessels have been studied in rats with chronic renal failure and in sham-operated rats. Brain microvessels isolated from rats with experimental chronic renal failure showed that the uptake of labeled large neutral amino acid, i.e., leucine or phenylalanine, but not of lysine or alpha-methylaminoisobutyric acid, was significantly increased with respect to sham-operated rats; conversely, the uptake of glutamic acid in rats with chronic renal failure was significantly lower compared with values in controls. Kinetic analysis indicated that this was mainly due to increased exchange transport activity (Vmax) of the L-system, rather than to changes in the affinity (Km) of the carrier system for the relative substrate. These data, together with the significant rise of brain glutamine levels and an increased brain-to-plasma ratio of the sum of large neutral amino acids, are analogous to what was previously observed in rats with portocaval anastomosis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ornithine decarboxylase activity in regenerating rat adrenal cortex

The activity of ornithine decarboxylase during the regenerating process of adrenal cortex was evaluated in Sprague-Dawley male rats weighing 140–180 g. In this study, 4 groups of rats were enucleated and another 4 groups were sham operated. Animals were maintained at a temperature of 23 ± 1°C and 12:12 h light:dark cycle. At 7 and 11 days post surgery, animals were sacrificed at 0600 h and 1800 h, respectively. Adrenal glands were immediately removed and assayed for ornithine decarboxylase (ODC). The enzyme activity was found to be significantly elevated in enucleated groups as compared to the sham control groups at the 7th and the 11th day of surgery. ODC activity was found to be about 2 times higher at 1800 h by the 7th day and 5 times higher at 1800 h by the 11th day of adrenal surgery when compared to the activity at 0600 h. From these results, it appears that ODC activity not only increases as the regeneration process of adrenal cortex approaches completion, but also becomes more pronounced towards the end of the light period.     

Effect of Jejunoileal Bypass on Plasma and Brain Amino Acids in the Rat

Abstract: Liver failure and coma are serious complications of Jejunoileal bypass (JIB) in man. Rats underwent either a 90–95% JIB or a sham operation. Six weeks later all animals were sacrificed, and plasma and brain amino acids were determined. In the plasma of rats with JIB compared with sham operation, the concentrations of valine, leucine, isoleucine, lysine, tryptophan, and tyrosine were significantly lower, while in the brain, phenylalanine, tyrosine, histidine, and glutamine were significantly higher. These changes in the brain are similar to those resulting from portalsystemic shunting in the rat.     

The effects of pinealectomy on pituitary and plasma gonadotropin levels in Carassius auratus exposed to various photoperiod–temperature regimes

The effects of pinealectomy on pituitary and plasma gonadotropin levels and gonadal development in female goldfish exposed to various photoperiod-temperature regimes during different seasons were examined. Pinealectomy during autumn had no effect on either pituitary or plasma hormone levels or gonadal development. When goldfish are pinealectomized in spring and exposed to long photoperiod conditions, the ovaries regress and plasma gonadotropin levels are significantly depressed compared to sham operated animals. Sham operated goldfish exposed to short photoperiod conditions in spring had regressing ovaries whereas pinealectomized animals under this regime either spawned or had ovaries in the late vitellogenic phase. Plasma gonadotropin titres in the pinealectomized group were significantly lower than those of sham operated animals. The pineal can be either stimulatory or inhibitory to gonadal development depending on the photoperiod regime to which the animals are exposed. The pineal apparently influences gonadal activity by modulating gonadotropin secretion. A diurnal variation in plasma gonadotropin levels was also observed in both sham operated and pinealectomized goldfish exposed to a long photoperiod warm-temperature regime in spring.     

Maze-escape learning and memory during rat ontogeny

With the method of a simple automatic rectangular maze the development of escape reaction was studied in albino rats aged 3 weeks to 3 months as well as memory retrieval within 24 h and then after one month. Learning of escape improves sharply between the 3rd and 4th postnatal week, and then, with the exception of week 8, remains approximately on the same level. Memory retrieval up to 24 h is not significantly influenced by age or sex, but is best immediately after learning interval of 10 min and the poorest after 24 h, except the age of 5 weeks, where it is best in 3 and 6 h after learning. One-month retention of maze escape improves during development except in animals trained at the age of 6 weeks in which the level is lower than in all other investigated groups. One-month memory retrieval in animals taught at the age of 4 weeks is influenced by the time of the first retention test with the best values in animals tested for the first time after 3 h and poorest in animals tested after 24 h after learning. Animals trained at 5 weeks had a marginally better result after the one-month retention test in females, perhaps due to the influence of sexual maturation on memory traces. This was not observed in the other age groups. Attention is drawn to the different development of learning and memory of various types of conditioned reactions stemming from the difference in their complexity.     

Uptake of Amino Acids by Brain Microvessels Isolated from Rats after Portacaval Anastomosis

Abstract: The uptake of amino acids by microvessels isolated from brains of rats was studied. Previous studies have demonstrated alterations in blood-brain amino acid transport after portacaval shunt in rats. In order to elucidate whether such changes in the blood-brain barrier were located in the microvessels, brain microvessels were isolated from both rats with portacaval shunt and controls. Brain microvessels from rats 2 weeks after shunt operations took up significantly greater amounts of ¹⁴C-labeled neutral amino acids, but not of glutamic acid. lysine, or α-methylaminoisobutyric acid than microvessels from sham-operated controls. Measurement of uptake kinetics showed a higher V _max for phenylalanine and leucine uptake and a lower V _max for lysine uptake in microvessels from shunted rats compared with control, whereas the respective K _m's of uptake were similar in both preparations. The results suggest that changes in brain microvessel transport activity account for altered brain neutral amino acid concentrations after portacaval shunt and that such changes can be studied in vitro in isolated microvessels.     

Albumin synthesis and catabolism following partial hepatectomy in the rat. The effects of amino acids and adrenocortical steroids on albumin synthesis after partial hepatectomy.

Plasma albumin levels were measured in partially hepatectomized, sham operated and control rats. The levels fell in both the partially hepatectomized and sham operated groups; while the latter group returned to normal within a few days, the low plasma albumin in the partially hepatectomized animals was sustained. Albumin synthesis rates in the isolated perfused rat liver were measured in the three groups of animals at varying intervals after partial hepatectomy. There was a significant depression of albumin synthesis rate in terms of both liver and whole animal weights when compared to the sham operated and control animals. This depression was almost completely reversed by the addition of arginine, asparagine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, threonine, tryptophan and valine added together to 10 times their normal plasma concentrations. The addition of hydrocortisone had no effect on the albumin synthesis rate after partial hepatectomy. Studies in vivo in the three groups of animals (partially hepatectomized, sham operated and control animals) revealed a fall in the albumin catabolic rate after partial hepatectomy coinciding with the fall in the albumin synthesis rate. An hypothesis whereby the amino acids may have their stimulatory effect is proposed.     

Cardiopulmonary bypass and long-term neurocognitive dysfunction in the rat

Neurologic and neurocognitive complications after cardiac surgery with cardiopulmonary bypass (CPB) have been reported repeatedly. To better understand its etiology and design protective strategies, an appropriate animal model may prove useful. Although impaired short-term neurocognitive function has been recently demonstrated after CPB in rats, the demonstration of persistent long-term neurocognitive changes would be more relevant from a clinical perspective. We hypothesized that CPB results in long-term impairment of neurocognitive performance in rats. Male rats were exposed to either 60 min of normothermic non-pulsatile CPB, using a roller-pump and a neonatal membrane oxygenator, or to cannulation only (sham animals). Long-term neurocognitive function was assessed at 4 to 7 weeks after CPB (Can test), and again after 12 weeks (Morris water maze) in both operated groups and in a non-operated control group, followed by histologic evaluation of the hippocampus. In separate groups of CPB and sham animals, we also measured TNF-alpha and IL-6 in plasma. There were no significant differences in long-term neurocognitive performance or histological outcome between the three groups. Cytokine patterns were also similar in both operated groups. We conclude that CPB did not appear to cause long-term neurocognitive dysfunction in this model of CPB in young healthy rats. The lack of long-term deficits may be due to the absence of clinically important etiologic factors such as atheromatous and gaseous embolization in this model. Similar cytokine patterns in both operated groups suggest that surgical trauma rather than exposure of blood to extra-corporeal circuit was probably responsible for the inflammatory response.     

Content of Quinolinic Acid and of Other Tryptophan Metabolites Increases in Brain Regions of Rats Used as Experimental Models of Hepatic Encephalopathy

The content of the tryptophan metabolites quinolinic acid (QUIN), 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) was measured in various brain areas of rats bearing a portocaval anastomosis (PCA) for 4 weeks, using mass fragmentography or HPLC. In these animals, the content of the excitotoxic compound QUIN increased by 75% in the cortex and 125% in the cerebellum. The content of 5-HT increased by 27% in the brainstem. No changes occurred in other brain areas. On the other hand, the content of 5-HIAA increased by 66% in the cortex, 65% in the caudate, 64% in the hippocampus, 120% in the diencephalon, and 185% in the brainstem. Probenecid administration caused a larger increase of 5-HIAA accumulation in various brain areas of PCA-bearing rats than in those of sham-operated controls. The cortical content of QUIN and 5-HIAA increased after administration of ammonium acetate (7 mmol/kg), whereas an equimolar amount of sodium acetate was inactive. These results confirm that profound changes in the disposition of tryptophan occur in the brains of experimental animals used as models of hepatic encephalopathy. Furthermore, this study adds the excitotoxic compound QUIN to the list of molecules possibly involved in the pathogenesis of this brain disorder.     

Amino acid neurotransmitters and their receptors in the brain synaptosomes of acute hepatic failure rats

Ammonia contents in the brain stem and prosencephalon markedly increased in a rat model of acute hepatic failure induced by partial hepatectomy following CCl4 intoxication. In hepatic failure rats, synaptosomal glutamic acid (excitatory amino acid neurotransmitter) contents decreased significantly in the prosencephalon, and GABA (inhibitory amino acid neurotransmitter) contents decreased significantly in the brain stem. The molar ratio of glutamic acid to glutamine significantly diminished in the brain stem. Glutamic acid decarboxylase activity in the synaptosomes and the binding of [3H]glutamic acid and [3H]GABA to synaptosomal membrane preparations were unchanged in acute hepatic failure rats. These results indicate than an insufficiency of both excitatory and inhibitory neurotransmitter amino acids is induced by high ammonia contents in the synaptosomes of the brain stem during acute hepatic failure.     

The right-to-left shunt of crocodilians serves digestion

Abstract All amniotes except birds and mammals have the ability to shunt blood past the lungs, but the physiological function of this ability is poorly understood. We studied the role of the shunt in digestion in juvenile American alligators in the following ways. First, we characterized the shunt in fasting and postprandial animals and found that blood was shunted past the lungs during digestion. Second, we disabled the shunt by surgically sealing the left aortic orifice in one group of animals, and we performed a sham surgery in another. We then compared postprandial rates of gastric acid secretion at body temperatures of 19 degrees and 27 degrees C and rates of digestion of bone at 27 degrees C. Twelve hours after eating, maximal rates of gastric acid secretion when measured at 19 degrees and 27 degrees C were significantly less in the disabled group than in sham-operated animals. Twenty-four hours postprandial, a significant decrease was found at 27 degrees C but not at 19 degrees C. For the first half of digestion, dissolution of cortical bone was significantly slower in the disabled animals. These data suggest the right-to-left shunt serves to retain carbon dioxide in the body so that it can be used by the gastrointestinal system. We hypothesize that the foramen of Panizza functions to enrich with oxygen blood that is destined for the gastrointestinal system to power proton pumps and other energy-demanding processes of digestion and that the right-to-left shunt serves to provide carbon dioxide to gastrointestinal organs besides the stomach, such as the pancreas, spleen, upper small intestine, and liver.     

MicroRNA-208a Increases Myocardial Fibrosis via Endoglin in Volume Overloading Heart

MicroRNA-208a (mir-208a) is essential for cardiac hypertrophy and fibrosis. Endoglin, a co-receptor of transforming growth factor-β is also essential for cardiac fibrosis. Endoglin has been shown to be a target of mir-208a in the in vitro mechanical stress model. Volume overload can lead to heart failure and cardiac fibrosis. The role of mir-208a and endoglin in volume overload heart failure is well known. We sought to investigate the mechanism of regulation of mir-208a and endoglin in volume overload-induced heart failure. Aorta-caval (AV) shunt was performed in adult Sprague-Dawley rats to induce volume overload. Heart weight and heart weight/body weight ratio significantly increased in AV shunt animals. AV shunt significantly increased left ventricular end-diastolic dimension as compared to sham group. Mir-208a was significantly induced by AV shunt from 3 to 14 days. Endoglin, myosin heavy chain-β and brain natriuretic peptide were significantly induced by AV shunt from 3 to 14 days. Overexpression of mir-208a in the sham group without AV shunt significantly increased endoglin expression similar to the AV shunt group. Antagomir-208a attenuated the endoglin expression induced by AV shunt. Pretreatment with atorvastatin also attenuated the endoglin expression induced by AV shunt. AV shunt significantly increased myocardial fibrosis as compared to sham group. Overexpression of mir-208a in the sham group significantly increased myocardial fibrosis. Antagomir-208a and atorvastatin significantly attenuated the myocardial fibrosis induced by AV shunt. In conclusion, mir-208a increased endoglin expression to induce myocardial fibrosis in volume overloaded heart failure. Treatment with atorvastatin can attenuate the myocardial fibrosis induced by volume overload through inhibition of endoglin expression.     

Compensatory growth of adipose tissue after partial lipectomy: involvement of serum factors

The regulation of body weight/fat was studied by investigating mechanisms for compensatory adipose tissue growth after removal of bilateral epididymal fat pads from male adult Wistar rats. Food intake during the first 4 weeks and energy expenditure on Days 8-10 postsurgery were not different between lipectomized and sham operated rats. During Days 29-31 post surgery, a small (2.4%) but significant (P < 0.05) increase in heat production per metabolic body size was detected in lipectomized as compared with sham operated rats. The carcass composition of lipectomized and sham operated rats was not significantly different 16 weeks after surgery. The compensatory growth was fat pad-specific: mesenteric, retroperitoneal, and inguinal fat pads, but not perirenal fat pads, were heavier in lipectomized rats than in sham operated rats as early as 4 weeks postsurgery. Examination of fat cell size distribution in the compensating pads indicated a shift toward larger cells in retroperitoneal fat, but not in inguinal fat of lipectomized as compared with sham operated rats. Serum from lipectomized rats, but not media conditioned by exposure to retroperitoneal fat pads from lipectomized rats, stimulated proliferation of preadipocytes in vitro more than that from sham operated rats. Thus, compensatory adipose tissue growth after lipectomy may be mediated, in part, by blood-borne factors that are derived from tissues other than adipose tissue.