Response of barren-ground caribou to advancing spring phenology.

Phenological shifts are occurring in many ecosystems around the world. The capacity of species to adapt to changing phenology will be critical to their success under climate change scenarios. Failure to adjust migratory and reproductive timing to keep pace with the earlier onset of spring has led to negative demographic effects for populations of species across a variety of taxa. For caribou, there have been concerns that earlier spring green-up on calving areas might not be matched by earlier migration and parturition, potentially leading to a trophic mismatch with nutritional consequences for parturient and lactating caribou cows. However, there is limited evidence supporting these concerns. Here, we investigate the response of barren-ground caribou to changing spring phenology using data from telemetry and satellite imagery. From 2004 to 2016, we found that the average start of green-up on the calving area advanced by 7.25 days, while the start of migration advanced by 13.64 days, the end of migration advanced by 6.02 days, and the date of peak calving advanced by 9.42 days. Despite the advancing onset of green-up, we found no evidence for the development of a trophic mismatch because the advancing green-up coincided with earlier migration and calving by caribou. Changing snow cover on the late winter and migratory ranges was the most supported driver of advancing migratory behavior. The ability of caribou to adjust the timing of migratory and reproductive behavior in response to changing environmental conditions demonstrates the potential resilience of the species to some aspects of climate change.

Investigation of Raman Spectroscopic Signatures with Multivariate Statistics: An Approach for Cataloguing Microbial Biosignatures.

Spectroscopic instruments are increasingly being implemented in the search for extraterrestrial life. However, microstructural spectral analyses of alien environments could prove difficult without knowledge on the molecular identification of individual spectral signatures. To bridge this gap, we introduce unsupervised K-means clustering as a statistical approach to discern spectral patterns of biosignatures without prior knowledge of spectral regions of biomolecules. Spectral profiles of bacterial isolates from analogous polar ice sheets were measured with Raman spectroscopy. Raman analysis identified carotenoid and violacein pigments, and key cellular features including saturated and unsaturated fats, triacylglycerols, and proteins. Principal component analysis and targeted spectra integration biplot analysis revealed that the clustering of bacterial isolates was attributed to spectral biosignatures influenced by carotenoid pigments and ratio of unsaturated/saturated fat peaks. Unsupervised K-means clustering highlighted the prevalence of the corresponding spectral peaks, while subsequent supervised permutational multivariate analysis of variance provided statistical validation for spectral differences associated with the identified cellular features. Establishing a validated catalog of spectral signatures of analogous biotic and abiotic materials, in combination with targeted supervised tools, could prove effective at identifying extant biosignatures.

Subpopulation structure of caribou (Rangifer tarandus L.) in arctic and subarctic Canada.

Effective management and conservation of species, subspecies, or ecotypes require an understanding of how populations are structured in space. We used satellite-tracking locations and hierarchical and fuzzy clustering to quantify subpopulations within the behaviorally different barren-ground caribou (Rangifer tarandus groenlandicus), Dolphin and Union island caribou (R. t. groenlandicus x pearyi), and boreal (R. t. caribou) caribou ecotypes in the Northwest Territories and Nunavut, Canada. Using a novel approach, we verified that the previously recognized Cape Bathurst, Bluenose-West, Bluenose-East, Bathurst, Beverly, Qamanirjuaq, and Lorillard barren-ground subpopulations were robust and that the Queen Maude Gulf and Wager Bay barren-ground subpopulations were organized as individuals. Dolphin and Union island and boreal caribou formed one and two distinct subpopulation, respectively, and were organized as individuals. Robust subpopulations were structured by strong annual spatial affiliation among females; subpopulations organized as individuals were structured by migratory connectivity, barriers to movement, and/or habitat discontinuity. One barren-ground subpopulation used two calving grounds, and one calving ground was used by two barren-ground subpopulations, indicating that these caribou cannot be reliably assigned to subpopulations solely by calving-ground use. They should be classified by annual spatial affiliation among females. Annual-range size and path lengths varied significantly among ecotypes, including mountain woodland caribou (R. t. caribou), and reflected behavioral differences. An east-west cline in annual-range sizes and path lengths among migratory barren-ground subpopulations likely reflected differences in subpopulation size and habitat conditions and further supported the subpopulation structure identified.

A proposed nomenclature and diagnostic criteria for protein-energy wasting in acute and chronic kidney disease.

The recent research findings concerning syndromes of muscle wasting, malnutrition, and inflammation in individuals with chronic kidney disease (CKD) or acute kidney injury (AKI) have led to a need for new terminology. To address this need, the International Society of Renal Nutrition and Metabolism (ISRNM) convened an expert panel to review and develop standard terminologies and definitions related to wasting, cachexia, malnutrition, and inflammation in CKD and AKI. The ISRNM expert panel recommends the term 'protein-energy wasting' for loss of body protein mass and fuel reserves. 'Kidney disease wasting' refers to the occurrence of protein-energy wasting in CKD or AKI regardless of the cause. Cachexia is a severe form of protein-energy wasting that occurs infrequently in kidney disease. Protein-energy wasting is diagnosed if three characteristics are present (low serum levels of albumin, transthyretin, or cholesterol), reduced body mass (low or reduced body or fat mass or weight loss with reduced intake of protein and energy), and reduced muscle mass (muscle wasting or sarcopenia, reduced mid-arm muscle circumference). The kidney disease wasting is divided into two main categories of CKD- and AKI-associated protein-energy wasting. Measures of chronic inflammation or other developing tests can be useful clues for the existence of protein-energy wasting but do not define protein-energy wasting. Clinical staging and potential treatment strategies for protein-energy wasting are to be developed in the future.

Adjunctive use of the Rinspiration system for fluidic thrombectomy during primary angioplasty: the Rinspiration international registry.

BACKGROUND: Atherothrombotic embolization during primary percutaneous coronary intervention (PCI) induces microvascular obstruction and reduces myocardial tissue reperfusion. A variety of thrombectomy devices have been evaluated as an adjunct to primary PCI in patients with ST-elevation myocardial infarction (STEMI) to reduce distal embolization. Results have been inconsistent and difficult to predict. The aim of this study was to investigate the safety and efficacy of an innovative thrombectomy device, the Rinspiration System, which simultaneously "rinses" the vessel with turbulent flow and aspirates thrombus. METHODS: We prospectively enrolled 109 patients at six academic institutions in three countries referred for primary or rescue PCI for STEMI presenting within 12 hr of symptom onset. The primary endpoint was >or=50% ST-segment elevation resolution (STR) measured 60 min after PCI by continuous electrocardiographic recording, Secondary end points included STR > 70% at 60 min, final TIMI flow, myocardial blush score, and 30-day major adverse cardiac events (MACE). RESULTS: Mean symptom-to-PCI time was 4.7 +/- 2.7 hr. Rinspiration was successfully delivered in 98% of cases. Final TIMI three flow was achieved in 89% of patients and myocardial blush >or=2 in 78%. Rates of STR >or= 50% and >70% at 60 min were 97 and 80%, respectively. No device-related complications were observed. Thirty-day MACE rate was 4.6%. CONCLUSIONS: This international multicenter registry demonstrates that the adjunctive use of Rinspiration during primary PCI is safe and feasible. The excellent STR data compare favorably with results of previous trials using different devices for thrombus management, indicating a potential clinical benefit.

Muscle protein turnover and glucose uptake in acutely uremic rats. Effects of insulin and the duration of renal insufficiency.

Acute renal failure (ARF) in rats is associated with increased amino acid release from peripheral tissues and insulin resistance. To study whether abnormal protein and carbohydrate metabolism are linked in ARF, the effects of insulin on net muscle protein degradation (T) and on glucose uptake were measured in the perfused hindquarters of paired ARF and sham-operated (SO) rats. The basal rate of T increased 40% after 24 and 98% after 48 h of ARF. Insulin was less effective in decreasing T in ARF (-79% SO vs. -22% ARF 24 h and -64% SO vs. -23% ARF 48 h; P less than 0.01). Protein synthesis (PS) and protein degradation (PD) were measured independently in incubated epitrochlearis muscles; the increase in T after 24 h of ARF was due specifically to increased PD, while PS was unchanged. At this stage, insulin was less effective in decreasing PD in ARF (-10% ARF vs. -23% SO; P less than 0.02), although PS responded normally. After 48 h of ARF, the further increment in T was caused by the additional appearance of depressed basal and insulin-stimulated PS. This was confirmed in the perfused hindquarter (26 +/- 3 ARF vs. 38 +/- 3 SO, basal; 54 +/- 5 ARF vs 73 +/- 7 SO, insulin-stimulated, nmol phenylalanine/g per h; P less than 0.05). Although basal glucose uptake by hindquarters of ARF and SO rats was comparable, insulin-stimulated glucose uptake was 33% less at 24 and 44% less after 48 h of ARF. After 48 h of ARF, lactate and alanine release were increased and net glycogen synthesis in muscle was depressed. These abnormalities were even more apparent in the presence of insulin. Inefficient glucose utilization, estimated as the ratio of lactate release to glucose uptake, was correlated with T (r = +0.78; P less than 0.001). In conclusion, after 24 h of ARF, both increased PD and altered glucose utilization could be detected. After 48 h of ARF, T increased further because PS was depressed. At this time, glucose utilization was clearly abnormal and the results suggest that abnormal net protein degradation in ARF may be a consequence of defective glucose utilization.

Mechanisms for defects in muscle protein metabolism in rats with chronic uremia. Influence of metabolic acidosis.

Chronic renal failure (CRF) is associated with metabolic acidosis and abnormal muscle protein metabolism. As we have shown that acidosis by itself stimulates muscle protein degradation by a glucocorticoid-dependent mechanism, we assessed the contribution of acidosis to changes in muscle protein turnover in CRF. A stable model of uremia was achieved in partially nephrectomized rats (plasma urea nitrogen, 100-120 mg/dl, blood bicarbonate less than 21 meq/liter). CRF rats excreted 22% more nitrogen than pair-fed controls (P less than 0.005), so muscle protein synthesis and degradation were measured in perfused hindquarters. CRF rats had a 90% increase in net protein degradation (P less than 0.001); this was corrected by dietary bicarbonate. Correction of acidosis did not reduce the elevated corticosterone excretion rate of CRF rats, nor did it improve a second defect in muscle protein turnover, a 34% lower rate of insulin-stimulated protein synthesis. Thus, abnormal nitrogen production in CRF is due to accelerated muscle proteolysis caused by acidosis and an acidosis-independent inhibition of insulin-stimulated muscle protein synthesis.

Metabolic acidosis stimulates protein degradation in rat muscle by a glucocorticoid-dependent mechanism.

Metabolic acidosis is associated with enhanced renal ammonia-genesis which is regulated, in part, by glucocorticoids. The interaction between glucocorticoids and chronic metabolic acidosis on nitrogen utilization and muscle protein metabolism is unknown. In rats pair-fed by gavage, we found that chronic acidosis stunted growth and caused a 43% increase in urinary nitrogen and an 87% increase in urinary corticosterone. Net protein degradation in incubated epitrochlearis muscles from chronically acidotic rats was stimulated at all concentrations of insulin from 0 to 10(4) microU/ml. This effect of acidosis persisted despite supplementation of the media with amino acids with or without insulin, indomethacin, and inhibitors of lysosomal thiol cathepsins. Acidosis did not change protein synthesis; hence, the increase in net protein degradation was caused by stimulation of proteolysis. Acidosis did not increase glutamine production in muscle. The protein catabolic effect of acidosis required glucocorticoids; protein degradation was stimulated in muscle of acidotic, adrenalectomized rats only if they were treated with dexamethasone. Moreover, when nonacidotic animals were given 3 micrograms/100 g of body weight dexamethasone twice a day, muscle protein degradation was increased if the muscles were simply incubated in acidified media. We conclude that chronic metabolic acidosis depresses nitrogen utilization and increases glucocorticoid production. The combination of increased glucocorticoids and acidosis stimulates muscle proteolysis but does not affect protein synthesis. These changes in muscle protein metabolism may play a role in the defense against acidosis by providing amino acid nitrogen to support the glutamine production necessary for renal ammoniagenesis.

Nitrogen sparing induced by leucine compared with that induced by its keto analogue, alpha-ketoisocaproate, in fasting obese man.

We measured the effects of seven consecutive daily infusions of alpha-ketoisocaproate (the alpha-keto analogue of leucine) or leucine itself on urinary urea and total nitrogen excretion during fasting. Two study protocols were undertaken. In protocol I, subjects underwent three separate 14-d fasts: one during which 34 mmol/d of leucine were infused on days 1--7; a second during which 34 mmol/d of alpha-ketoisocaproate were infused on days 1--7; and a third control fast during which no infusions were given. Infusions of alpha-ketoisocaproate significantly reduced daily urine urea nitrogen excretion compared with both the control fasts and the fasts in which leucine was infused (P less than 0.001). This nitrogen-sparing effect of alpha-ketoisocaproate persisted during days 8--14 even though no further infusions were given. Daily urinary urea nitrogen excretion during fasts when leucine was administered did not differ from values observed during control fasts. In protocol II, subjects were starved on two occasions for 14 d. During one fast, infusions of 11 mmol/d of alpha-ketoisocaproate were given on days 1--7; during the control fast, no infusions were given. Daily urine urea nitrogen excretion was lower (P less than 0.001) on days 1--7 and also on days 8--14 of the fast during which alpha-ketoisocaproate was given. The nitrogen-sparing effect of alpha-ketoisocaproate could not be related to changes in circulating levels of amino acids, ketone bodies, or insulin in either protocol. We conclude that alpha-ketoisocaproate infusions decrease the nitrogen wasting of starvation, whereas leucine, studied under identical conditions, does not.

Systemic response to thermal injury in rats. Accelerated protein degradation and altered glucose utilization in muscle.

Negative nitrogen balance and increased oxygen consumption after thermal injury in humans and experimental animals is related to the extent of the burn. To determine whether defective muscle metabolism is restricted to the region of injury, we studied protein and glucose metabolism in forelimb muscles of rats 48 h after a scalding injury of their hindquarters. This injury increased muscle protein degradation (PD) from 140 +/- 5 to 225 +/- 5 nmol tyrosine/g per h, but did not alter protein synthesis. Muscle lactate release was increased greater than 70%, even though plasma catecholamines and muscle cyclic AMP were not increased. Insulin dose-response studies revealed that the burn decreased the responsiveness of muscle glycogen synthesis to insulin but did not alter its sensitivity to insulin. Rates of net glycolysis and glucose oxidation were increased and substrate cycling of fructose-6-phosphate was decreased at all levels of insulin. The burn-induced increase in protein and glucose catabolism was not mediated by adrenal hormones, since they persisted despite adrenalectomy. Muscle PGE2 production was not increased by the burn and inhibition of prostaglandin synthesis by indomethacin did not inhibit proteolysis. The increase in PD required lysosomal proteolysis, since inhibition of cathepsin B with EP475 reduced PD. Insulin reduced PD 20% and the effects of EP475 and insulin were additive, reducing PD 41%. An inhibitor of muscle PD, alpha-ketoisocaproate, reduced burn-induced proteolysis 28% and lactate release 56%. The rate of PD in muscle of burned and unburned rats was correlated with the percentage of glucose uptake that was directed into lactate production (r = +0.82, P less than 0.01). Thus, a major thermal injury causes hypercatabolism of protein and glucose in muscle that is distant from the injury, and these responses may be linked to a single metabolic defect.

Abnormal cation transport in uremia. Mechanisms in adipocytes and skeletal muscle from uremic rats.

The cause of the abnormal active cation transport in erythrocytes of some uremic patients is unknown. In isolated adipocytes and skeletal muscle from chronically uremic chronic renal failure rats, basal sodium pump activity was decreased by 36 and 30%, and intracellular sodium was increased by 90 and 50%, respectively, compared with pair-fed control rats; insulin-stimulated sodium pump activity was preserved in both tissues. Lower basal NaK-ATPase activity in adipocytes was due to a proportionate decline in [3H]ouabain binding, while in muscle, [3H]ouabain binding was not changed, indicating that the NaK-ATPase turnover rate was decreased. Normal muscle, but not normal adipocytes, acquired defective Na pump activity when incubated in uremic sera. Thus, the mechanism for defective active cation transport in CRF is multifactorial and tissue specific. Sodium-dependent amino acid transport in adipocytes closely paralleled diminished Na pump activity (r = 0.91), indicating the importance of this defect to abnormal cellular metabolism in uremia.

Dichloroacetate inhibits glycolysis and augments insulin-stimulated glycogen synthesis in rat muscle.

The decrease in plasma lactate during dichloroacetate (DCA) treatment is attributed to stimulation of lactate oxidation. To determine whether DCA also inhibits lactate production, we measured glucose metabolism in muscles of fed and fasted rats incubated with DCA and insulin. DCA increased glucose-6-phosphate, an allosteric modifier of glycogen synthase, approximately 50% and increased muscle glycogen synthesis and glycogen content greater than 25%. Lactate release fell; inhibition of glycolysis accounted for greater than 80% of the decrease. This was associated with a decrease in intracellular AMP, but no change in citrate or ATP. When lactate oxidation was increased by raising extracellular lactate, glycolysis decreased (r = - 0.91), suggesting that lactate oxidation regulates glycolysis. When muscle lactate production was greatly stimulated by thermal injury, DCA increased glycogen synthesis, normalized glycogen content, and inhibited glycolysis, thereby reducing lactate release. The major effect of DCA on lactate metabolism in muscle is to inhibit glycolysis.

The acidosis of chronic renal failure activates muscle proteolysis in rats by augmenting transcription of genes encoding proteins of the ATP-dependent ubiquitin-proteasome pathway.

Chronic renal failure (CRF) is associated with negative nitrogen balance and loss of lean body mass. To identify specific proteolytic pathways activated by CRF, protein degradation was measured in incubated epitrochlearis muscles from CRF and sham-operated, pair-fed rats. CRF stimulated muscle proteolysis, and inhibition of lysosomal and calcium-activated proteases did not eliminate this increase. When ATP production was blocked, proteolysis in CRF muscles fell to the same level as that in control muscles. Increased proteolysis was also prevented by feeding CRF rats sodium bicarbonate, suggesting that activation depends on acidification. Evidence that the ATP-dependent ubiquitin-proteasome pathway is stimulated by the acidemia of CRF includes the following findings: (a) An inhibitor of the proteasome eliminated the increase in muscle proteolysis; and (b) there was an increase in mRNAs encoding ubiquitin (324%) and proteasome subunits C3 (137%) and C9 (251%) in muscle. This response involved gene activation since transcription of mRNAs for ubiquitin and the C3 subunit were selectively increased in muscle of CRF rats. We conclude that CRF stimulates muscle proteolysis by activating the ATP-ubiquitin-proteasome-dependent pathway. The mechanism depends on acidification and increased expression of genes encoding components of the system. These responses could contribute to the loss of muscle mass associated with CRF.

Ubiquitin conjugation by the N-end rule pathway and mRNAs for its components increase in muscles of diabetic rats.

Insulin deficiency (e.g., in acute diabetes or fasting) is associated with enhanced protein breakdown in skeletal muscle leading to muscle wasting. Because recent studies have suggested that this increased proteolysis is due to activation of the ubiquitin-proteasome (Ub-proteasome) pathway, we investigated whether diabetes is associated with an increased rate of Ub conjugation to muscle protein. Muscle extracts from streptozotocin-induced insulin-deficient rats contained greater amounts of Ub-conjugated proteins than extracts from control animals and also 40-50% greater rates of conjugation of (125)I-Ub to endogenous muscle proteins. This enhanced Ub-conjugation occurred mainly through the N-end rule pathway that involves E2(14k) and E3alpha. A specific substrate of this pathway, alpha-lactalbumin, was ubiquitinated faster in the diabetic extracts, and a dominant negative form of E2(14k) inhibited this increase in ubiquitination rates. Both E2(14k) and E3alpha were shown to be rate-limiting for Ub conjugation because adding small amounts of either to extracts stimulated Ub conjugation. Furthermore, mRNA for E2(14k) and E3alpha (but not E1) were elevated 2-fold in muscles from diabetic rats, although no significant increase in E2(14k) and E3alpha content could be detected by immunoblot or activity assays. The simplest interpretation of these results is that small increases in both E2(14k) and E3alpha in muscles of insulin-deficient animals together accelerate Ub conjugation and protein degradation by the N-end rule pathway, the same pathway activated in cancer cachexia, sepsis, and hyperthyroidism.

Glomerular function in Pima Indians with noninsulin-dependent diabetes mellitus of recent onset.

Differential solute clearances were used to characterize glomerular function in 20 Pima Indians with noninsulin-dependent diabetes mellitus (NIDDM) of less than 3 yr duration. 28 Pima Indians with normal glucose tolerance served as controls. In the diabetic group, the glomerular filtration rate (GFR, iothalamate clearance) exceeded the control value by 15% (140 +/- 6 vs. 122 +/- 5 ml/min, P less than 0.01). A corresponding 12% increase in renal plasma flow (RPF) was not statistically significant and did not account fully for the observed hyperfiltration, suggesting a concomitant elevation of the ultrafiltration pressure or coefficient. The median albumin excretion ratio in NIDDM exceeded control by almost twofold (10.1 vs. 5.8 mg/g creatinine), a trend which just failed to achieve statistical significance (P = 0.06). Fractional clearances of dextrans of broad size distribution were also elevated in diabetic subjects, significantly so for larger dextrans of between 48 and 60 A radius. A theoretical analysis of dextran transport through a heteroporous membrane revealed glomerular pores in NIDDM to be uniformly shifted towards pores of larger size than in controls. We conclude that an impairment of barrier size selectivity combined with high GFR elevates the filtered protein load in NIDDM of recent onset. We propose that enhanced transglomerular trafficking of protein may predispose to sclerosis of glomeruli in those Pima Indians with NIDDM who ultimately develop diabetic nephropathy.

Muscle wasting in insulinopenic rats results from activation of the ATP-dependent, ubiquitin-proteasome proteolytic pathway by a mechanism including gene transcription.

In normal subjects and diabetic patients, insulin suppresses whole body proteolysis suggesting that the loss of lean body mass and muscle wasting in insulinopenia is related to increased muscle protein degradation. To document how insulinopenia affects organ weights and to identify the pathway for accelerated proteolysis in muscle, streptozotocin-treated and vehicle-injected, pair-fed control rats were studied. The weights of liver, adipose tissue, and muscle were decreased while muscle protein degradation was increased 75% by insulinopenia. This proteolytic response was not eliminated by blocking lysosomal function and calcium-dependent proteases at 7 or 3 d after streptozotocin. When ATP synthesis in muscle was inhibited, the rates of proteolysis were reduced to the same level in insulinopenic and control rats suggesting that the ATP-dependent, ubiquitin-proteasome pathway is activated. Additional evidence for activation of this pathway in muscle includes: (a) an inhibitor of proteasome activity eliminated the increased protein degradation; (b) mRNAs encoding ubiquitin and proteasome subunits were increased two- to threefold; and (c) there was increased transcription of the ubiquitin gene. We conclude that the mechanism for muscle protein wasting in insulinopenia includes activation of the ubiquitin-proteasome pathway with increased expression of the ubiquitin gene.

Metabolic acidosis stimulates muscle protein degradation by activating the adenosine triphosphate-dependent pathway involving ubiquitin and proteasomes.

Metabolic acidosis often leads to loss of body protein due mainly to accelerated protein breakdown in muscle. To identify which proteolytic pathway is activated, we measured protein degradation in incubated epitrochlearis muscles from acidotic (NH4Cl-treated) and pair-fed rats under conditions that block different proteolytic systems. Inhibiting lysosomal and calcium-activated proteases did not reduce the acidosis-induced increase in muscle proteolysis. However, when ATP production was also blocked, proteolysis fell to the same low level in muscles of acidotic and control rats. Acidosis, therefore, stimulates selectively an ATP-dependent, nonlysosomal, proteolytic process. We also examined whether the activated pathway involves ubiquitin and proteasomes (multicatalytic proteinases). Acidosis was associated with a 2.5- to 4-fold increase in ubiquitin mRNA in muscle. There was no increase in muscle heat shock protein 70 mRNA or in kidney ubiquitin mRNA, suggesting specificity of the response. Ubiquitin mRNA in muscle returned to control levels within 24 h after cessation of acidosis. mRNA for subunits of the proteasome (C2 and C3) in muscle were also increased 4-fold and 2.5-fold, respectively, with acidosis; mRNA for cathepsin B did not change. These results are consistent with, but do not prove that acidosis stimulates muscle proteolysis by activating the ATP-ubiquitin-proteasome-dependent, proteolytic pathway.

Interactions between L-arginine and L-glutamine change endothelial NO production. An effect independent of NO synthase substrate availability.

The effect of extracellular L-arginine and L-glutamine on nitric oxide (NO) release was studied in cultured bovine aortic endothelial cells and in rabbit aortic rings. Increasing L-arginine (0.01 to 10 mM) did not alter NO release from cultured endothelial cells or modify endothelium-dependent relaxation to acetylcholine in isolated vessels. L-Glutamine (0.6 and 2 mM) inhibited NO release from cultured cells (in response to bradykinin) and from aortic rings (in response to acetylcholine or ADP). L-Arginine (0.1-10 mM) dose-dependently reversed the L-glutamine inhibition of receptor-stimulated NO release in both models. In contrast to its inhibitory response to receptor-mediated stimuli, glutamine alone slightly potentiated NO release in both models when the calcium ionophore, A23187, was added. Furthermore, cultured cells incubated with L-arginine (0.01-10 mM), in the presence or absence of glutamine, released similar amounts of NO in response to A23187. L-Glutamine did not affect intracellular L-arginine levels. Neither D-glutamine nor D-arginine affected NO release or endothelium-dependent vascular relaxation. L-Glutamine had no effect on the activity of endothelial NOS assessed by L-arginine to L-citrulline conversion. These findings show that in the absence of L-glutamine, manipulating intracellular L-arginine levels over a wide range does not affect NO release. L-Glutamine in concentrations circulating in vivo may tonically inhibit receptor-mediated NO release by interfering with signal transduction. One mechanism by which L-arginine may enhance NO release is via reversal of the inhibitory effect of L-glutamine, but apparently independently of enhancing NO synthase substrate.

Drug eluting stents and the critical path initiative: Evolving paradigms for safety evaluation.

Recent discussions between FDA and other stakeholders have focused on the benefits and risks associated with drug eluting stents (DES). A particular topic of focus is DES thrombosis, a rare, but serious, clinical event that may occur months to years after the initial implantation. FDA continues vigilant postmarket surveillance of DES currently on the market and is working with stent manufactures to ensure that new DES platforms in the development pipeline are safe and effective. FDA is also taking steps, under its Critical Path Initiative (CPI) [FDA. Innovation or Stagnation: Challenge and Opportunity on the Critical Path to New Medical Products, March 2004.http://www.fda.gov/oc/initiatives/criticalpath/whitepaper.html], to help address current and future DES safety issues. This article describes some of these activities.:

Metabolic and clinical consequences of metabolic acidosis.

Acid-base balance is precisely regulated by pulmonary and renal responses while body buffers help to control pH. When its regulation becomes abnormal, accumulation of hydrogen ions cause metabolic acidosis and several responses are activated. These responses interfere with the metabolism of bones and muscle. Metabolic acidosis induces abnormalities in the release and function of several hormones including defects in growth hormone, IGF-1, insulin, glucocorticoids, thyroid hormone, parathyroid hormone and vitamin D. Clinical consequences of these abnormal metabolic responses include impaired growth of infants and children and loss of bone and muscle mass in adults. Notably, abnormalities in bone and muscle metabolism can be present even when there is little or no decrease in the plasma bicarbonate concentration. The abnormalities can be corrected by treatment with NaHCO 3 . In patients with chronic kidney disease, many abnormalities in bone and muscle metabolism can be directly linked to the presence of metabolic acidosis and these abnormalities can be largely corrected by treating acidosis with NaHCO3. Recent insights indicate that several consequences of metabolic acidosis including the development of insulin resistance can stimulate muscle protein degradation by activating proteolytic mechanisms. To avoid abnormalities in metabolism and the loss of bone and muscle, metabolic acidosis must be corrected in normal adults and in patients with kidney disease.