The effects of hypoosmotic infusion on the composition of renal tissue of the Australian brush-tailed possum Trichosurus vulpecula

Although the occurrence of organic osmolytes in the inner medulla of the marsupial kidney has been recently reported [Comp. Biochem. Physiol. (2002) 132B 635-644], changes in these substances, in response to water loading in vivo, has not been studied. Adult Trichosurus vulpecula, the Australian brush-tailed possum, were subjected to water deprivation for 48 h. Following anaesthesia and unilateral nephrectomy, the animals were perfused with hypo-osmotic saline (80 mmol l(-1); 1.5 ml min(-1)) for 60 min. This resulted in a rapid increase in urine volume and a corresponding fall in urine osmolality. At the end of the infusion the animals were killed and the second kidney removed. Analysis of the renal tissue revealed that water content of cortical, outer and inner medullary regions of the kidney increased slightly following infusion, while sodium, and chloride contents of all three regions fell. Potassium contents, on the other hand, were barely changed. Of the organic osmolytes determined, very significant decreases in the inner medulla, following infusion, were found for sorbitol (from 397+/-79 to 266+/-49 mmol kg(-1) protein), inositol (247+/-23 to 190+/-25 mmol kg(-1) protein), and betaine (464+/-70 to 356+/-21 mmol kg(-1) protein), while only inositol was significantly decreased in the outer medulla (197+/-22 to 150+/-16 mmol kg(-1) protein). Glycerophosphorylcholine levels were low throughout the kidney and were not significantly affected by the infusion. It was concluded that inositol and sorbitol play a significant role as compatible organic osmolytes in the possum kidney, while betaine functions as the principal counteracting osmolyte. Amino acid levels in the cortex and outer medulla showed no overall change in amount following infusion, although there were highly significant changes in individual amino acids. In the inner medulla there was a highly significant reduction in total amino acids with infusion, largely due to a fall in amounts of taurine (104+/-4 to 75+/-17 mmol kg(-1) protein), and glycine (97+/-15 to 71+/-18 mmol kg(-1) protein). A fall in free amino acid levels in the inner medulla appears to significantly contribute to the process of intracellular osmotic adjustment during an induced diuresis.     

Osmotic effectors in kidneys of xeric and mesic rodents: corticomedullary distributions and changes with water availability

Summary Urea, sodium, the methylamines glycine betaine and glycerophosphorylcholine (GPC), and the polyols sorbitol and myo-inositol are reported to be the major osmolytes in kidneys of laboratory mammals. These were measured (millimoles per kilogram wet weight) in kidney regions and urines of three species of wild rodents with different dehydration tolerances: the pocket mousePerognathus parvus (xeric), voleMicrotus montanus (mesic), and deer mousePeromyscus m. gambeli (intermediate). In animals kept without water for 4–6 days, sodium, urea, betaine and GPC+choline were found in gradients increasing from cortex to outer to inner medulla in all species, withPerognathus having the highest levels. Sorbitol was high in the inner medulla but low in the cortex and outer medulla; inositol was highest in the outer medulla. Totals of methylamines and methylamines plus polyols in the medulla showed high linear correlations (positive) with urea and with sodium values.Whole medullae were analyzed at several time points inMicrotus andPeromyscus subject to water diuresis followed by antidiuresis. In 102 h diuresis inMicrotus, all osmolytes decreased except inositol; however, only urea, sodium and sorbitol reached new steady states within 24 h. Urea returned to initial values in 18 h antidiuresis, while other osmolytes required up to 90 h. InPeromyscus, all osmolytes except the polyols declined in diuresis (max. 78 h test period). During antidiuresis, urea and GPC+choline rose to initial values in 18 h, with sodium and betaine requiring more time. In plots of both species combined, total methylamines+polyols correlated linearly (positive) with sodium, and GPC+choline with urea.Estimates of tissue concentrations suggest that total methylamines+polyols can account for intracellular osmotic balance in all species in antidiuresis and that sufficient concentrations of methylamines may be present to counteract perturbing effects of urea on proteins.Abbrevations GPC Glycero-3-phosphorylcholine - TCA trichloroacetic acid - M+P methylamines plus polyols     

Diversity in levels of intracellular total creatine and triglycerides in human skeletal muscles observed by (1)H-MRS.

We used (1)H-magnetic resonance spectroscopy to noninvasively determine total creatine (TCr), choline-containing compounds (Cho), and intracellular (IT) and extracellular (between-muscle fibers) triglycerides (ET) in three human skeletal muscles. Subjects' (n = 15 men) TCr concentrations in soleus [Sol; 100.2 +/- 8.3 (SE) mmol/kg dry wt] were lower (P < 0.05) than those in gastrocnemius (Gast; 125.3 +/- 9.2 mmol/kg dry wt) and tibialis anterior (TA; 123. 7 +/- 8.8 mmol/kg dry wt). The Cho levels in Sol (35.8 +/- 3.6 mmol/kg dry wt) and Gast (28.5 +/- 3.5 mmol/kg dry wt) were higher (P < 0.001 and P < 0.01, respectively) compared with TA (13.6 +/- 2. 4 mmol/kg dry wt). The IT values were found to be 44.8 +/- 4.6 and 36.5 +/- 4.2 mmol/kg dry wt in Sol and Gast, respectively. The IT values of TA (24.5 +/- 4.5 mmol/kg dry wt) were lower than those of Sol (P < 0.01) and Gast (P < 0.05). There were no differences in ET [116.0 +/- 11.2 (Sol), 119.1 +/- 18.5 (Gast), and 91.4 +/- 19.2 mmol/kg dry wt (TA)]. It is proposed that the differences in metabolite levels may be due to the differences in fiber-type composition and deposition of metabolites due to the adaptation of different muscles during locomotion.     

Organic osmolytes in the developing kidney of the Australian brush-tailed possum, Trichosurus vulpecula

Developmental changes in the plasma and urine composition of 120 immature possums, Trichosurus vulpecula, were investigated and correlated with changes in the osmolyte composition of the kidneys. In early life, when the animal is confined in the pouch, the urine is more or less isosmotic with the plasma (300+/-70 mOsm kg(-1)), but rises steeply in animals more than 90 days old, up to 667+/-53 mOsm kg(-1) in the oldest age group. In parallel with this change there are corresponding increases in medullary osmolytes. Measured as mmol kg(-1) wet weight, sorbitol was found to increase from 2.1+/-0.8 to 9.7+/-2.2, myo-inositol from 10.9+/-6.2 to 33.6+/-11.7, while the methylamines glycerophosphorylcholine and betaine rose from 6.2+/-0.5 to 15.3+/-3.1 and 3.9+/-2.2 to 9.4+/-2.5 mmol kg(-1) wet weight respectively. Medullary taurine showed no significant changes with age in young possums, while urea increased from 11+/-4.6 to 49+/-7.1 mmol kg(-1) wet weight. These values are similar to, but less than, those found in adult kidneys, but probably further refinement of the concentrating ability of the kidney occurs after the young animal becomes independent.     

Pyruvate overrides inhibition of PDH during exercise after a low-carbohydrate diet

The effects of carbohydrate deprivation on the regulation of pyruvate dehydrogenase (PDH) were studied at rest and during moderate-intensity exercise. An inhibitory effect of a chronic low-carbohydrate diet (LCD) on the active form of PDH (PDHa) mediated by a stable increase in PDH kinase (PDHK) activity has recently been reported (Peters SJ, Howlett RA, St. Amand TA, Heigenhauser GJF, and Spriet LL. Am J Physiol Endocrinol Metab 275: E980-E986, 1998.). In the present study, seven males cycled at 65% maximal O(2) uptake for 30 min after a 6-day LCD. Exercise was repeated 1 wk later after a mixed diet (MD). Muscle biopsies were sampled from the vastus lateralis at rest and at 2 and 30 min of exercise. At rest, PDHa activity (0.18 +/- 0.04 vs. 0.63 +/- 0.18 mmol x min(-1) x kg wet wt(-1)), muscle glycogen content (310.2 +/- 36.9 vs. 563.9 +/- 32.6 mmol/kg dry wt), and muscle lactate content (2.6 +/- 0.3 vs. 4.2 +/- 0.6 mmol/kg dry wt) were significantly lower after the LCD. Resting muscle acetyl-CoA (10.8 +/- 1.9 vs. 7.4 +/- 0.8 micromol/kg dry wt) and acetylcarnitine (5.3 +/- 1.4 vs. 1.6 +/- 0.3 mmol/kg dry wt) contents were significantly elevated after the LCD. During exercise, PDHa, glycogenolytic rate (LCD 5.8 +/- 0.4 vs. MD 6.9 +/- 0.2 mmol x min(-1) x kg dry wt(-1)), and muscle concentrations of acetylcarnitine, pyruvate, and lactate increased to the same extent in both conditions. The results of the present study suggest that inhibition of resting PDH by elevated PDHK activity after a LCD may be overridden by the availability of muscle pyruvate during exercise.     

Dysregulation of muscle lipid metabolism in rats selectively bred for low aerobic running capacity

As substrate for evaluation of metabolic diseases, we developed novel rat models that contrast for endurance exercise capacity. Through two-way artificial selection, we created rodent phenotypes of intrinsically low-capacity runners (LCR) and high-capacity runners (HCR) that also differed markedly for cardiovascular and metabolic disease risk factors. Here, we determined skeletal muscle proteins with putative roles in lipid and carbohydrate metabolism to better understand the mechanisms underlying differences in whole body substrate handling between phenotypes. Animals (generation 16) differed for endurance running capacity by 295%. LCR animals had higher resting plasma glucose (6.58 +/- 0.45 vs. 6.09 +/- 0.45 mmol/l), insulin (0.48 +/- 0.03 vs. 0.32 +/- 0.02 ng/ml), nonesterified fatty acid (0.57 +/- 0.14 v 0.35 +/- 0.05 mM), and triglyceride (TG; 0.47 +/- 0.11 vs. 0.25 +/- 0.08 mmol/l) concentrations (all P < 0.05). Muscle TG (72.3 +/- 14.7 vs. 38.9 +/- 6.2 mmol/kg dry muscle wt; P < 0.05) and diacylglycerol (96 +/- 28 vs. 42 +/- 8 pmol/mg dry muscle wt; P < 0.05) contents were elevated in LCR vs. HCR rats. Accompanying the greater lipid accretion in LCR was increased fatty acid translocase/CD36 content (1,014 +/- 80 vs. 781 +/- 70 arbitrary units; P < 0.05) and reduced TG lipase activity (0.158 +/- 0.0125 vs. 0.274 +/- 0.018 mmol.min(-1).kg dry muscle wt(-1); P < 0.05). Muscle glycogen, GLUT4 protein, and basal phosphorylation states of AMP-activated protein kinase-alpha1, AMP-activated protein kinase-alpha2, and acetyl-CoA carboxylase were similar in LCR and HCR. In conclusion, rats with low intrinsic aerobic capacity demonstrate abnormalities in lipid-handling capacity. These disruptions may, in part, be responsible for the increased risk of metabolic disorders observed in this phenotype.     

Polyol determination along the rat nephron

The polyols sorbitol and inositol were determined in single freshly microdissected tubule segments of rat kidney. Twenty different structures were separated from six different kidney zones reaching from cortex to papillary tip. Picomol amounts of sorbitol and inositol were quantitated by use of an enzymatic bioluminescence procedure. Experimental conditions (700 mosmol/kg, 4 degrees C) were chosen to assure constant polyol concentrations over 3 h dissection period. Sorbitol exhibited a concentration gradient in the collecting duct system from the outer/inner medullary border (3.9 +/- 0.5 pmol/mm) to the papillary tip (78.8 +/- 6.9 pmol/mm). In the same region descending and ascending limbs of Henle's loop contained 1.5 +/- 0.5 to 5.3 +/- 1.6 pmol/mm and 2.5 +/- 0.8 to 8.35 +/- 1.5 pmol/mm, respectively. In contrast, all outer medullary and cortical structures had lower sorbitol concentrations. Inositol amounts increased continuously in the collecting duct from cortex (5.3 +/- 0.5 pmol/mm) to inner medulla (30.7 +/- 3.8 pmol/mm). This polyol was also found in thick ascending limb of Henle's loop (6.2 +/- 1.1 pmol/mm in cortex to 11.2 +/- 1.4 pmol/mm in outer medulla) and in proximal tubules (5.6 +/- 1.2 pmol/mm in S1 and 4.5 +/- 1.5 pmol/mm in S3). When related to cellular volume measured by planimetry, intracellular sorbitol concentration was calculated to be 51 mmol/l in papillary collecting duct and inositol 28 mmol/l in outer medullary thick ascending limb cells. These data confirm the role of sorbitol in the renal concentrating process in papilla. Inositol seems to have additional function in thick ascending limb of Henle's loop and the proximal tubule.     

Effects of 7 wk of endurance training on human skeletal muscle metabolism during submaximal exercise.

This is the first study to examine the effects of endurance training on the activation state of glycogen phosphorylase (Phos) and pyruvate dehydrogenase (PDH) in human skeletal muscle during exercise. We hypothesized that 7 wk of endurance training (Tr) would result in a posttransformationally regulated decrease in flux through Phos and an attenuated activation of PDH during exercise due to alterations in key allosteric modulators of these important enzymes. Eight healthy men (22 +/- 1 yr) cycled to exhaustion at the same absolute workload (206 +/- 5 W; approximately 80% of initial maximal oxygen uptake) before and after Tr. Muscle biopsies (vastus lateralis) were obtained at rest and after 5 and 15 min of exercise. Fifteen minutes of exercise post-Tr resulted in an attenuated activation of PDH (pre-Tr: 3.75 +/- 0.48 vs. post-Tr: 2.65 +/- 0.38 mmol.min(-1).kg wet wt(-1)), possibly due in part to lower pyruvate content (pre-Tr: 0.94 +/- 0.14 vs. post-Tr: 0.46 +/- 0.03 mmol/kg dry wt). The decreased pyruvate availability during exercise post-Tr may be due to a decreased muscle glycogenolytic rate (pre-Tr: 13.22 +/- 1.01 vs. post-Tr: 7.36 +/- 1.26 mmol.min(-1).kg dry wt(-1)). Decreased glycogenolysis was likely mediated, in part, by posttransformational regulation of Phos, as evidenced by smaller net increases in calculated muscle free ADP (pre-Tr: 111 +/- 16 vs. post-Tr: 84 +/- 10 micromol/kg dry wt) and P(i) (pre-Tr: 57.1 +/- 7.9 vs. post-Tr: 28.6 +/- 5.6 mmol/kg dry wt). We have demonstrated for the first time that several signals act to coordinately regulate Phos and PDH, and thus carbohydrate metabolism, in human skeletal muscle after 7 wk of endurance training.     

The nitrogen requirements and dietary nitrogen utilization for the gecarcinid land crab Gecarcoidea natalis

The nitrogen requirements for tissue maintenance, moulting, and oogenesis were determined experimentally for the herbivorous land crab Gecarcoidea natalis. The maintenance nitrogen requirements for intermoult animals was very low (4.83+/-1.68 mmol N kg-1 dry body wt d-1), but during oogenesis the total requirement was much higher (8. 6 mmol N kg-1 dry body wt d-1). Gecarcoidea natalis could potentially assimilate enough nitrogen from rain forest leaf litter or leaves of Ficus or Erythrina to satisfy not only the maintenance nitrogen requirements but the observed rate of incorporation of nitrogen into the ovaries during oogenesis. The ovaries developed slowly over a period of 2 mo (mid-July to late September) and had a final nitrogen content of 359+/-15.9 (n=18) mmol kg-1 dry body wt. This was equivalent to 9.3%+/-0.4% of the total body nitrogen. A substantial nitrogen debt was incurred during ecdysis (658+/-126 mmol kg-1 dry body wt). This nitrogen debt could be satisfied slowly, from leaf litter, over a period of 1-3 mo. After ecdysis, the majority of the nitrogen and urate within the animal prior to moulting was retained within the soft crab (85.0%+/-1.2% total nitrogen, 82.0%+/-1.2% nonurate nitrogen and 99.56% urate), while only a minority was lost with the exuviae (18.0%+/-1.2% total nitrogen, 14.7%+/-1.2% nonurate nitrogen, and 0.4%+/-0.4% urate). The urate deposits in G. natalis were not mobilized as a source of nitrogen in animals maintained on a nitrogen-free diet.     

Creatine phosphate in fiber types of skeletal muscle before and after exhaustive exercise

Percutaneous muscle biopsies were obtained from the vastus lateralis of physically active men (n = 12) 1) at rest, 2) immediately after an exercise bout consisting of 30 maximal voluntary knee extensions of constant angular velocity (3.14 rad/s), and 3) 60 s after termination of exercise. Creatine phosphate (CP) content was analyzed in pools of freeze-dried fast-twitch (FT) and slow-twitch (ST) muscle fiber fragments, and ATP, CP, creatine, and lactate content were assayed in mixed pools of FT and ST fibers. CP content at rest was 82.7 +/- 11.2 and 73.1 +/- 9.5 (SD) mmol/kg dry wt in FT and ST fibers (P less than 0.05). After exercise the corresponding values were 25.4 +/- 19.8 and 29.7 +/- 14.4 mmol/kg dry wt. After 60 s of recovery CP increased (P less than 0.01) to 41.3 +/- 12.6 and 49.6 +/- 11.7 mmol/kg dry wt in FT and ST fibers, respectively. CP content after recovery, relative to initial level, was higher in ST compared with FT fibers (P less than 0.05). ATP content decreased (P less than 0.05) and lactate content rose to 67.4 +/- 28.3 mmol/kg dry wt (P less than 0.001) in response to exercise. It is concluded that basal CP content is higher in FT fibers than in ST fibers. CP content also appears to be higher in ST fibers after a 60-s recovery period after maximal short-term exercise. These data are consistent with the different metabolic profiles of FT and ST fibers.     

Metabolic regulation of organic osmolytes in tubules from rat renal inner and outer medulla

Glycerophosphorylcholine (GPC), sorbitol and inositol were quantitated in renal tubule suspensions from inner and outer medulla of untreated Sprague-Dawley rats to study the regulation of organic osmolyte concentrations under different metabolic conditions and varying extracellular osmolalities in vitro. Inner medullary tubules prepared in hypertonic saline (550 mosm/kg) contained osmolyte concentrations comparable to those found in the kidney in vivo. Incubation for up to 8 h at 5 mmol/l glucose increased sorbitol in the inner medullary tubules and medium in an osmolality-dependent fashion, whereas GPC and inositol remained constant. At a given glucose concentration the rate of sorbitol formation decreased linearly with increasing tubular sorbitol concentration, which was regulated by an osmolality-dependent export mechanism. Perturbation of tubular mechanisms by inhibition of glycolysis or oxidative phosphorylation did not change the tubular osmolyte content. In contrast to papilla outer medullary tubules contained only inositol. Lactate added as a metabolic substrate to the outer medullary tubules did not change the cellular inositol levels. In outer medullary tubules osmolality changes (320-710 mosm/kg) had no effect on tubular inositol. Addition of furosemide was without effect, when added in vitro. The results indicate that tubular sorbitol formation is regulated by glucose concentration, the level of tubular sorbitol, and an osmolality-dependent export mechanism. In contrast, cellular inositol and GPC levels seem to be independent of acute changes in tubular metabolism.     

Muscle glycogen resynthesis during recovery from cycle exercise: no effect of additional protein ingestion.

In the present study, we have investigated the effect of carbohydrate and protein hydrolysate ingestion on muscle glycogen resynthesis during 4 h of recovery from intense cycle exercise. Five volunteers were studied during recovery while they ingested, immediately after exercise, a 600-ml bolus and then every 15 min a 150-ml bolus containing 1) 1.67 g. kg body wt(-1). l(-1) of sucrose and 0.5 g. kg body wt(-1). l(-1) of a whey protein hydrolysate (CHO/protein), 2) 1.67 g. kg body wt(-1). l(-1) of sucrose (CHO), and 3) water. CHO/protein and CHO ingestion caused an increased arterial glucose concentration compared with water ingestion during 4 h of recovery. With CHO ingestion, glucose concentration was 1-1.5 mmol/l higher during the first hour of recovery compared with CHO/protein ingestion. Leg glucose uptake was initially 0.7 mmol/min with water ingestion and decreased gradually with no measurable glucose uptake observed at 3 h of recovery. Leg glucose uptake was rather constant at 0.9 mmol/min with CHO/protein and CHO ingestion, and insulin levels were stable at 70, 45, and 5 mU/l for CHO/protein, CHO, and water ingestion, respectively. Glycogen resynthesis rates were 52 +/- 7, 48 +/- 5, and 18 +/- 6 for the first 1.5 h of recovery and decreased to 30 +/- 6, 36 +/- 3, and 8 +/- 6 mmol. kg dry muscle(-1). h(-1) between 1.5 and 4 h for CHO/protein, CHO, and water ingestion, respectively. No differences could be observed between CHO/protein and CHO ingestion ingestion. It is concluded that coingestion of carbohydrate and protein, compared with ingestion of carbohydrate alone, did not increase leg glucose uptake or glycogen resynthesis rate further when carbohydrate was ingested in sufficient amounts every 15 min to induce an optimal rate of glycogen resynthesis.     

Glucose formation in human skeletal muscle. Influence of glycogen content.

Eight men exercised at 66% of their maximal isometric force to fatigue after prior decrease in the glycogen store in one leg (low-glycogen, LG). The exercise was repeated with the contralateral leg (control) at the same relative intensity and for the same duration. Muscle (quadriceps femoris) glycogen content decreased in the LG leg from 199 +/- 17 (mean +/- S.E.M.) to 163 +/- 16 mmol of glucosyl units/kg dry wt. (P less than 0.05), and in the control leg from 311 +/- 23 to 270 +/- 18 mmol/kg (P less than 0.05). The decrease in glycogen corresponded to a similar accumulation of glycolytic intermediates. Muscle glucose increased in the LG leg during the contraction, from 1.8 +/- 0.1 to 4.3 +/- 0.6 mmol/kg dry wt. (P less than 0.01), whereas no significant increase occurred in the control leg (P greater than 0.05). It is concluded that during exercise glucose is formed from glycogen through the debranching enzyme when muscle glycogen is decreased to values below about 200 mmol/kg dry wt.     

Gene expression reveals vulnerability to oxidative stress and interstitial fibrosis of renal outer medulla to nonhypertensive elevations of ANG II

The present study was designed to determine whether nonhypertensive elevations of plasma ANG II would modify the expression of genes involved in renal injury that could influence oxidative stress and extracellular matrix formation in the renal medulla using microarray, Northern, and Western blot techniques. Sprague-Dawley rats were infused intravenously with either ANG II (5 ng. kg(-1). min(-1)) or vehicle for 7 days (n = 6/group). Mean arterial pressure averaged 110 +/- 0.6 mmHg during the control period and 113 +/- 0.4 mmHg after ANG II. The mRNA of 1,751 genes ( approximately 80% of all currently known rat genes) that was differentially expressed (ANG II vs. saline) in renal outer and inner medulla was determined. The results of 12 hybridizations indicated that in response to ANG II, 11 genes were upregulated and 25 were downregulated in the outer medulla, while 11 were upregulated and 13 were downregulated in the inner medulla. These differentially expressed genes, most of which were not known previously to be affected by ANG II in the renal medulla, were found to group into eight physiological pathways known to influence renal injury and kidney function. Particularly, expression of several genes would be expected to increase oxidative stress and interstitial fibrosis in the outer medulla. Western blot analyses confirmed increased expression of transforming growth factor-beta1 and collagen type IV proteins in the outer medulla. Results demonstrate that nonhypertensive elevations of plasma ANG II can significantly alter the expression of a variety of genes in the renal outer medulla and suggested the vulnerability of the renal outer medulla to the injurious effect of ANG II.     

Predominant osmotically active organic solutes in rat and rabbit renal medullas

The mechanism that concentrates the urine to an osmolality several times that of systemic plasma results in high concentrations of solutes (particularly NaCl and urea) in extracellular fluid of renal medulla, but not in the labyrinth of the renal cortex. Intracellular and extracellular osmolality must be equal in animals, but the known intracellular levels of Na and K salts and urea in renal medullas are much too low to balance the high extracellular osmolality. The purpose of these studies was to identify the other intracellular osmolytes that must be present. Cortexes and medullas from rabbit and rat kidneys were analyzed by proton nuclear magnetic resonance, mass spectrometry, and chemical assays to determine the identity and amount of organic solutes. Large amounts of glycerophosphorylcholine, betaine, sorbitol, and inositol were found in both species localized almost exclusively to the inner medulla. In rabbits during antidiuresis glycerophosphorylcholine, betaine, and sorbitol were present in the inner medulla, at concentrations of 21.1, 34.8, and 20.8 mumol/g wet weight, respectively, but were not detected in the cortex. Inositol was present in rabbit inner medulla at 10.7 mumol/g wet weight and was also present in the cortex, but at lower concentration. None of the above metabolites was present in measurable amounts in urine or peripheral plasma. The accumulation in the cells of the inner medulla of relatively large amounts of betaine, sorbitol, glycerophosphorylcholine and inositol during antidiuresis suggests that they may play a significant role in the maintenance of intracellular osmotic balance.     

Salicylate nephropathy in the Gunn rat: potential role of prostaglandins

We examined the potential role of prostaglandins in the development of analgesic nephropathy in the Gunn strain of rat. The homozygous Gunn rats have unconjugated hyperbilirubinemia due to the absence of glucuronyl transferase, leading to marked bilirubin deposition in renal medulla and papilla. These rats are also highly susceptible to develop papillary necrosis with analgesic administration. We used homozygous (jj) and phenotypically normal heterozygous (jJ) animals. Four groups of rats (n = 7) were studied: jj and jJ rats treated either with aspirin 300 mg/kg every other day or sham-treated. After one week, slices of cortex, outer and inner medulla from one kidney were incubated in buffer and prostaglandin synthesis was determined by radioimmunoassay. The other kidney was examined histologically. A marked corticomedullary gradient of prostaglandin synthesis was observed in all groups. PGE2 synthesis was significantly higher in outer medulla, but not cortex or inner medulla, of jj (38 +/- 6 ng/mg prot) than jJ rats (15 +/- 3) (p less than 0.01). Aspirin treatment reduced PGE2 synthesis in all regions, but outer medullary PGE2 remained higher in jj (18 +/- 3) than jJ rats (9 +/- 2) (p less than 0.05). PGF2 alpha was also significantly higher in the outer medulla of jj rats with and without aspirin administration (p less than 0.05). The changes in renal prostaglandin synthesis were accompanied by evidence of renal damage in aspirin-treated jj but not jJ rats as evidenced by: increased incidence and severity of hematuria (p less than 0.01); increased serum creatinine (p less than 0.05); and increase in outer medullary histopathologic lesions (p less than 0.005 compared to either sham-treated jj or aspirin-treated jJ). These results suggest that enhanced prostaglandin synthesis contributes to maintenance of renal function and morphological integrity, and that inhibition of prostaglandin synthesis may lead to pathological renal medullary lesions and deterioration of renal function.     

Taurine protects against carbon tetrachloride toxicity in the cultured neurons and in vivo

Carbon tetrachloride (CCl4) has been found to induce cellular damage by generating oxygen free radicals. A study was carried out to investigate the effects of taurine (extracted from Pegasus laternarius Cuvier) on CCl4 intoxicated cultured neurons. CCl4 application (0.4 mmol x l(-1), 0.8 mmol x l( -1), 1.2 mmol x l (-1) and 1.6 mmol x l(-1 )) increased the lipid peroxidation product and decreased glutathione peroxidase (GPx) activity significantly in a concentration dependent manner. Pretreatment of cultures with taurine (10 micromol x l(-1), 30 micromol x l(-1) and 60 micromol x l(-1)) prevented the loss of GPx activity and lipid peroxidation. The effects of three different dosages of taurine (10 mg/kg body wt., 20 mg/kg body wt. and 40 mg/ kg body wt.) for 45 days on the activities of superoxide dismutase and glutathione peroxidase were examined in the cerebrum, cerebellum and medulla of normal and CCl4 treated mice. Treatment of mice with taurine provided protection against CCl4 toxicity as was evident by lipid peroxide status. Taurine was not so successful at inducing the activity of SOD in normal animals except in the medulla where it could increase the activity of SOD (p < 0.05). Taurine induces the GPx activity in a dose dependent manner in all regions of the brain studied. Also in the CCl4 poisoned mice taurine could augment the status of GPx activity in a dose dependent manner. Hence it is concluded that taurine can protects neurons from the oxidative stress induced by CCl4.     

Effect of endurance training on muscle TCA cycle metabolism during exercise in humans.

We tested the theory that links the capacity to perform prolonged exercise with the size of the muscle tricarboxylic acid (TCA) cycle intermediate (TCAI) pool. We hypothesized that endurance training would attenuate the exercise-induced increase in TCAI concentration ([TCAI]); however, the lower [TCAI] would not compromise cycle endurance capacity. Eight men (22 +/- 1 yr) cycled at approximately 80% of initial peak oxygen uptake before and after 7 wk of training (1 h/day, 5 days/wk). Biopsies (vastus lateralis) were obtained during both trials at rest, after 5 min, and at the point of exhaustion during the pretraining trial (42 +/- 6 min). A biopsy was also obtained at the end of exercise during the posttraining trial (91 +/- 6 min). In addition to improved performance, training increased (P < 0.05) peak oxygen uptake and citrate synthase maximal activity. The sum of four measured TCAI was similar between trials at rest but lower after 5 min of exercise posttraining [2.7 +/- 0.2 vs. 4.3 +/- 0.2 mmol/kg dry wt (P < 0.05)]. There was a clear dissociation between [TCAI] and endurance capacity because the [TCAI] at the point of exhaustion during the pretraining trial was not different between trials (posttraining: 2.9 +/- 0.2 vs. pretraining: 3.5 +/- 0.2 mmol/kg dry wt), and yet cycle endurance time more than doubled in the posttraining trial. Training also attenuated the exercise-induced decrease in glutamate concentration (posttraining: 4.5 +/- 0.7 vs. pretraining: 7.7 +/- 0.6 mmol/kg dry wt) and increase in alanine concentration (posttraining: 3.3 +/- 0.2 vs. pretraining: 5.6 +/- 0.3 mmol/kg dry wt; P < 0.05), which is consistent with reduced carbon flux through alanine aminotransferase. We conclude that, after aerobic training, cycle endurance capacity is not limited by a decrease in muscle [TCAI].     

Dynamics of renal medullary vinculin under changing of osmoregulating function

Reduction of vinculin occurs in the renal medulla under the long-lasting dehydration. The protein content measured in inner medulla of rats of the WAG line under hydration was 92.1 +/- 6.3 in relative units, but it was only 77.6 +/- 2.3 after a 3-day water deprivation. The vinculin content in the inner medullar layer from mutant rats of Brattleboro line incapable of synthesizing vasopressin is essentially higher: it is 188.9 +/- 8.5 in hydrated conditions and drops to 148.4 +/- 7.3 under a 3-day dehydration. The same high level of vinculin is in outer medulla from rats of Brattleboro line: 222.1 +/- 11.8 in hydrated animals and 174.9 +/- 11 after a 3-day dehydration. No differences were revealed in response of vinculin to alternative osmoregulating stimulation in cortex in both rat lines.     

Human skeletal muscle exercise metabolism following an expedition to mount denali

Chronic exposure to high altitude is known to result in changes in the mechanisms regulating O(2) delivery to the contracting muscle. However, the effects of acclimatization on metabolism in the contracting muscle cell remain unclear. In this study, we have investigated the hypothesis that acclimatization would result in a closer coupling between ATP utilization and ATP production and that the improved energy state would be accompanied by a reorganization of the metabolic pathways consisting of an increased oxidative and decreased glycolytic potential. Five men, mean age of 28 +/- 2 (SE) yr, performed a standardized, two-stage submaximal cycling task in normoxia for 20 min at each of 59 and 74% peak O(2) consumption before and 3-4 days after returning from a 21-day expedition to Mount Denali (6,194 m). Acclimatization was without effect in altering the resting values of the adenine nucleotides (ATP, ADP, AMP), inosine monophosphate (IMP), or phosphocreatine (PCr) in the vastus lateralis. During exercise (40 min) after acclimatization compared with preacclimatization, PCr was not as depressed (33.2 +/- 7.1 vs. 40.6 +/- 5.4 mmol/kg dry wt) and IMP (0.289 +/- 0.11 vs. 0. 131 +/- 0.03 mmol/kg dry wt) and lactate (26.1 +/- 6.2 vs. 18.6 +/- 8.8 mmol/kg dry wt) in contracting muscle were not as elevated (P < 0.05). Although no effect of acclimatization was observed for the maximal activity (mol. kg protein(-1). h(-1)) of citrate synthase (4. 76 +/- 0.44 vs. 4.94 +/- 0.45), lactate dehydrogenase was increased by 13% (36.5 +/- 2.6 vs. 41.2 +/- 3.1, P < 0.05). It is concluded that acclimatization results in an improved energy state in the contracting muscle when tested under normoxic conditions; however, these effects are not associated with a higher oxidative potential or a lower glycolytic potential as hypothesized.