Differences In Maximal Rate Research Articles

Lipid Testing Trends Before and After Hospitalization for Myocardial Infarction Among Adults in the United States, 2008-2019.

BackgroundRoutine monitoring of low-density lipoprotein cholesterol (LDL-C) identifies patients who may benefit from modifying lipid-lowering therapies (LLT). However, the extent to which LDL-C testing is occurring in clinical practice is unclear, specifically among patients hospitalized for a myocardial infarction (MI).MethodsUsing US commercial claims data, we identified patients with an incident MI hospitalization between 01/01/2008-03/31/2019. LDL-C testing was assessed in the year before admission (pre-MI) and the year after discharge (post-MI). Changes in LDL-C testing were evaluated using a Poisson model fit to pre-MI rates and extrapolated to the post-MI period. We predicted LDL-C testing rates if no MI had occurred (ie, based on pre-MI trends) and estimated rate differences and ratios (contrasting observed vs predicted rates).ResultsOverall, 389,367 patients were hospitalized for their first MI during the study period. In the month following discharge, 9% received LDL-C testing, increasing to 27% at 3 months and 52% at 12 months. Mean rates (tests per 1000 patients per month) in the pre- and post-MI periods were 51.9 (95% CI: 51.7, 52.1) and 84.4 (95% CI: 84.1, 84.6), respectively. Over 12 months post-MI, observed rates were higher than predicted rates; the maximum rate difference was 66 tests per 1000 patients in month 2 (rate ratio 2.2), stabilizing at a difference of 15–20 (ratio 1.2–1.3) for months 6–12.ConclusionAlthough LDL-C testing increased following MI hospitalization, rates remained lower than recommended by clinical guidelines. This highlights a potential gap in care, where increased LDL-C testing after MI may provide opportunities for LLT modification and decrease risk of subsequent cardiovascular events.

Metabolic homeostasis: oxidative phosphorylation and the metabolic requirements of higher plants and animals.

A model of oxidative phosphorylation and its regulation is presented, which is consistent with the experimental data on metabolism in higher plants and animals. The variables that provide real-time control of metabolic status are: intramitochondrial [NAD+]/[NADH], energy state ([ATP]/[ADP][Pi]), and local oxygen concentration ([O2]). ATP consumption and respiratory chain enzyme content are tissue specific (liver vs. heart muscle), and the latter is modulated by chronic alterations in ATP consumption (i.e., endurance training etc.). ATP consumption affects the energy state, which increases or decreases as necessary to match synthesis with consumption. [NAD+]/[NADH], local [O2], and respiratory chain content determine the energy state at which match of synthesis and utilization is achieved. Tissues vary widely in their ranges of ATP consumption. Expressed as the turnover of cytochrome c, the rates may change little (7 to 12/s) (liver) or a lot (1 to >300/s) (flight muscle of birds, bats, and insects). Ancillary metabolic pathways, including creatine or arginine kinase, glycerol phosphate shuttle, fatty acid, and citric acid cycle dehydrogenases, are responsible for meeting tissue-specific differences in maximal rate and range in ATP utilization without displacing metabolic homeostasis. Intramitochondrial [NAD+]/[NADH], [ATP], and [Pi] are adjusted to keep [ADP] and [AMP] similar for all tissues despite large differences in ranges in ATP utilization. This is essential because [ADP] and [AMP], particularly the latter, have major roles in regulating the activity of many enzymes and signaling pathways (AMP deaminase, AMP dependent protein kinases, etc.) common to all higher plants and animals.NEW & NOTEWORTHY Oxidative phosphorylation has an intrinsic program that sets and stabilizes cellular energy state ([ATP]/[ADP][Pi]), and thereby metabolic homeostasis. A computational model consistent with regulation of oxidative phosphorylation in higher plants and animals is presented. Focus is on metabolism ancillary to oxidative phosphorylation by which it was integrated into preexisting metabolic regulation and adapted by evolution to develop cells and tissues with differing rates of ATP utilization: i.e., liver versus brain versus muscle.

Heritable variation in reaction norms of metabolism and activity across temperatures in a wild-derived population of white-footed mice (Peromyscus leucopus)

Heritable variation in metabolic traits is likely to affect fitness. In this study, white-footed mice from wild-derived photoresponsive [R, infertile in short day length (SD)] and non-photoresponsive (NR, fertile in SD) selection lines were maintained under short-day (SD 8Light:16Dark), sub-thermoneutral conditions (22 or 12°C). Mice had significantly higher levels of food intake and resting metabolic rates (RMR) at low temperature. RMR differed significantly between lines (greater in NR mice). In contrast to previous work under thermoneutral conditions, there was no significant difference in overall activity or average daily metabolic rates (ADMR) of mice from the two lines. Reduced activity may reflect behavioral changes under cooler conditions (e.g., nest building) reducing the overall energetic cost of fertility (for NR mice). There was no significant difference in maximal rate of oxygen consumption ([Formula: see text]) between lines. R mice had significantly greater brown adipose tissue and white abdominal fat mass due to both line and temperature. Reaction norms for intake, resting metabolism (RMR/BMR) and level of activity from current (12 and 22°C) and previously published data (28°C) demonstrate independent effects of genetics (line) and environment (temperature) for resting metabolism, but a clear interaction between these for activity. The results suggest that fertility under winter conditions imposes metabolic costs that are related to the level of reproductive development. Under the coldest conditions tested, however, mice that remained fertile in SD reduced activity, ADMR and food requirements, decreasing the differential between selection lines. Heritable variation in reaction norms suggests a genetic by environment effect that could be subject to selection.

Sex-related differences in maximal rate of isometric torque development

Sex-differences in the maximum rate of torque development (dτ/dtmax) may be due to differences in maximum muscle strength, because higher torque values mathematically lead to higher values for the rate of change in torque. The rate of change in the isometric torque-time curve is often normalized to the isometric maximum voluntary contraction (MVC) to evaluate males and females on a relative scale. Normalization eliminates sex-differences in dτ/dtmax in the lower limbs because males and females are more comparable (i.e., differences between the sexes are relatively small) with respect to both muscle size and strength. However, normalization fails to result in parody in dτ/dtmax of the upper limb, leading to the idea that other factors may be involved. This study determined if sex-differences in dτ/dtmax in the upper limb can be attributed to differences in isometric MVC and/or a neural variable related to rate of increase in muscle activation (Q30). Forty-six participants (23 males, 23 females) performed maximal isometric elbow flexion contractions, “as hard and as fast as possible”. Maximum torque (τmax), dτ/dtmax, and the rate of increase in surface electromyographic (sEMG) activity (Q30) were assessed. Muscle plus bone cross-sectional area (M+B CSA) of the upper arm was calculated to estimate differences in muscle size, only for comparative purposes. Maximum strength (55.5%) and muscle size (41.9%) of the elbow flexors in males were much greater than that of females (p<0.05). There was a large difference (61.2%) between males and females with respect to dτ/dtmax that was reduced by statistical correction using an analysis of covariance (ANCOVA). The percent differences were reduced to 36.7% (p<0.05) for τmax and 54.4% (p<0.05) for Q30, but was nearly eliminated to 13.8% (p>0.05) when both variables were used simultaneously as covariates. Since sex-differences in the upper limb dτ/dtmax persist, additional neural or biomechanical factors may be involved.

Cortico-motoneuronal excitation of three hand muscles determined by a novel penta-stimulation technique.

The cortico-motoneuronal system (CMS), i.e. the monosynaptic projection from primary motor cortex to motoneurons in lamina IX of the spinal cord is, among all mammals, best developed in humans. Increasing evidence suggests that the CMS is crucially important for skilled individuated finger movements. Little is known about to what extent the strength of the CMS differs between hand muscles. Here we measured CMS excitation to the first dorsal interosseus (FDI), abductor pollicis brevis (APB) and abductor digiti minimi (ADM) muscles in healthy subjects by using a novel penta-stimulation technique (PST) and single motor unit (SMU) recordings. The PST is an extension of the triple-stimulation technique. It applies two additional supramaximal electrical stimuli at the wrist to the 'peripheral nerve of no interest' (in the case of the FDI and ADM the median nerve, in the case of the APB the ulnar nerve) to collide with the descending volleys in that nerve elicited by transcranial magnetic stimulation of motor cortex and electrical stimulation of Erb's point. This eliminates volume conduction from neighbouring muscles innervated by the nerve of no interest and, therefore, allows accurate determination of the PST response. The PST response was significantly larger in the FDI compared with the ADM and APB. This was validated by the SMU recordings, which showed a higher estimated amplitude of the mean compound excitatory postsynaptic potential in spinal motoneurons of the FDI than in those of the APB and ADM. Finally, as a possible functional correlate, the maximum rate of repetitive voluntary finger movements was higher for index finger abduction (prime mover, FDI) than for little finger abduction (prime mover, ADM) and thumb abduction (prime mover, APB), and individual differences in maximum rate between the different movements correlated with individual differences in the corresponding PST responses. In conclusion, PST is a valuable novel method for accurate quantification of CMS excitation. The findings strongly suggest that CMS excitation differs between hand muscles and that these differences directly link to capability differences in individuated finger movements.

Nitroprusside reverses lengthened time of contraction in stunned canine cardiac myocytes.

We tested the hypothesis that stunning reduces the function of isolated canine ventricular myocytes and that nitroprusside (NP) reverses this effect. After stunning (15 min occlusion, 45 min reperfusion), isolated myocytes were prepared from control (circumflex artery) and stunned (left anterior descending) regions of the hearts of seven dogs. The myocytes were examined at baseline and with NP (10(-6,-5,-4) M) for oxygen consumption (MVO2, nl O2/min/10(5) cells), cyclic guanosine monophosphate (cyclic GMP; fmol/10(5) cells), and cell contraction. Basal MVO2 was not significantly different between control and stunned myocytes (888 +/- 108 vs. 716 +/- 94). NP caused a dose dependent decrease in MVo2 (control, 262 +/-51; stunned, 287 +/- 59, NP 10(-4) M). Basal cyclic GMP levels were comparable between control and stunned myocytes (117 +/-28 vs. 124 +/- 18). NP produced a similar dose-dependent increase in cyclic GMP in control and stunned myocytes. Baseline cell shortening (%) was similar in control vs. stunned myocytes (12.1 +/- 1.2 vs. 11.0 +/- 0.9). NP reduced shortening (6.9 +/- 0.3 vs. 7.3 +/- 0.5, NP 10(-4) M). There was no baseline difference in maximal rate of shortening (microm/s) between control and stunned myocytes (164 +/- 14, 157 +/- 20). With NP, a decrease in the maximal rate of shortening was seen in both groups (128 +/- 12, 139 +/- 21, NP 10(-4) M). The time of contraction (s) was significantly longer in stunned (0.20 +/- 0.03) versus control (0.13 +/- 0.01). NP significantly lengthened the time of contraction in controls in a dose-dependent manner (0.33 +/-0.05, NP 10(-4) M). In stunned myocytes, however, low-dose NP (10(-6) M) caused a decrease in the time of contraction (0.15 +/-0.03). High-dose NP (10(-4) M) did not significantly lengthen time of contraction in stunned cells (0.23 +/- 0.02). The time of relaxation followed a similar pattern. We conclude that part of the effect of NP in low doses in stunned myocardium is to reduce the lengthened time of contraction and relaxation characteristic of stunning.

Aerobic performance does not affect social rank in female Red Jungle Fowl

1. Exercise capacity ultimately constrains behaviour, and therefore may influence social interactions. The hypothesis was tested that individual differences in maximal rates of oxygen consumption (V·O2max) – a primary determinant of sustainable exercise capacity – affect dominance hierarchies in experimental all‐female flocks of the highly social Red Jungle Fowl (Gallus gallus). It was also examined whether social rank could in turn influence V·O2max (which is quite plastic in most vertebrates), and whether these relationships were influenced by a common and relatively benign parasite, the intestinal nematode Ascaridia galli. 2. Substantial between‐individual variation was found in V·O2max that was significantly repeatable over time, but there was no indication that V·O2max was affected by A. galli infection. Stable social hierarchies were quickly established in 26 of 28 experimental flocks (each contained three females previously isolated from each other). Infection status affected social rank, but there was no consistent pattern between rank and infection. 3. No indication was found that individual differences in V·O2max either predicted the social rank in newly formed flocks, or were affected by social status in established flocks.

Reducing Systemic Absorption from Monochloracetic Acid Exposure Through Dermal Decontamination: Use of the Pig Ear Organ Culture System

AbstractSevere systemic intoxication may occur after skin contamination with monochloracetic acid (MCA). For this reason the effects of decontaminating with either water (most commonly used) or bicarbonate on the rates of percutaneous penetration and dermal accumulation of radiolabeled MCA were measured using the blood-perfused pig ear model. The rate of percutaneous penetration of a 40% solution of MCA was measured after exposure times of 1, 3, and 10 min. Maximal rates of percutaneous penetration (ng/min/cm2; mean ± SEM) were 891 ± 335 for a 1 min exposure; 947 ± 191 for a 3 min exposure; and 3221 ± 515 for a 10 min exposure. Although the initial rate of percutaneous absorption (first 30 min) was directly related to the exposure time, there was no difference in maximal rates of percutaneous penetration for 1 and 3 min exposures. It appears, that for short exposure times, the percutaneous penetration rate is determined by both the rate of penetration into the skin and the rate of diffusion from dermal st...

Acid-catalyzed transannular cyclization of medium ring unsaturated sulfides. The effect of ring size and double bond geometry on rate

The acid-catalyzed transannular cyclization of 8–10-membered γ,δ-unsaturated cyclic sulfides yields cis fused bicyclic sulfonium salts independently of the geometry of the double bond. The rate varies linearly with the acidity function –(H0)I with a slope of 1. The rate variations span about six powers of ten range, the maximum rate difference being observed for the E/Z thiacyclooct-4-ene pair. The data are consistent with the classical interpretation of the intramolecular reactivity in terms of internal strain of the substrate and/or of the transition state.

Glucose sensing and signalling properties in Saccharomyces cerevisiae require the presence of at least two members of the glucose transporter family.

The kinetics of glucose transport in a number of different mutants of Saccharomyces cerevisiae with multiple deletions in the glucose transporter gene family were determined. The deletions led to differences in maximal rate and affinity for glucose uptake by the cells, dependent on the growth conditions. At the same time, there were changes in glucose repression, as determined by expression of invertase activity. Only in the strain with genes HXT1-4 and SNF3 deleted but carrying HXT6/7 were glucose uptake kinetics and invertase activity independent of the presence or concentration of glucose in the growth medium. Some degree of glucose sensitivity was recovered if the SNF3 or HXT2 gene was present in the multiple-deletion background. It is hypothesized that during growth on glucose, both modulation of the kinetics of glucose uptake and derepression of invertase activity require the presence of more than one active gene of the glucose transporter family.

Upland tundra in the foothills of the Brooks Range, Alaska: Influence of light, water content and temperature on CO2 exchange of characteristic lichen species

In a previous publication we described diel courses of CO 2 exchange and microclimate conditions for characteristic lichens in their natural habitat within upland tundra communities of northern Alaska. The influence of individual environmental factors on net photosynthesis (NP) of Cetraria cucullata, Dactylina arctica, Masonhalea richardsonii, Peltigera aphthosa, Peltigera malacea, Stereocaulon alpinum , and Thamnolia vermicularis was analyzed in the present study. CO 2 exchange measurements were conducted in the laboratory, and clear response characteristics with respect to light, water content (WC), temperature, and external CO 2 concentration were established under controlled conditions. In addition, dependencies of NP on these factors were extracted from field data. These measurements show a high scatter in data points, however, they represent the range of actual performance of the lichens under natural conditions. In general both, field and laboratory data sets, agree well with respect to absolute rates of photosynthetic capacity as well as response characteristics. The combined information from both sources enable us to identify and describe those physiological features which are relevant for photosynthetic production of the lichens at this tundra site. There were large differences in maximal rates of NP attained under natural ambient CO 2 which were expressed more strongly under conditions of CO 2 saturation. Photosynthetic capacity of the cyanobacterial P. malacea is ten times higher than that of the green algal M. richardsonii . In the field, actual photosynthesis often seemed to be depressed due to photoinhibition. Photosynthetic carbon gain occurred even with thallus temperatures of −10°C, while the temperature optimum of NP was between 11 and 22°C. Most of the species responded to supra-optimal degrees of WC with a pronounced depression in NP. Elevated ambient CO 2 concentration prevented this decrease in NP, indicating that it was caused by increased resistance of the thallus to CO 2 diffusion. Depression of NP at high thallus WC regularly occurred under natural conditions, impairing primary production. Response characteristic of the lichens to experimental increase in ambient CO 2 is highly dependent on thallus hydration. At optimal WC some species are already saturated by natural ambient CO 2 at least at lower light intensities. Possible future increase in natural ambient CO 2 concentration will impact lichen NP in particular when the thalli are highly water saturated.

Effect of daily photon receipt on the susceptibility of dwarf bean (Phaseolus vulgaris L.) leaves to photoinhibition of photosynthesis

Bean (Phaseolus vulgaris L.) plants were grown at two light periods of 8 and 13 h with a similar photon flux density (PFD) giving a daily photon receipt (DPR) of 17.9 and 38.2 mol · m−2, respectively. Shoot growth and leaf area development were followed at regular intervals and diurnal whole-plant photosynthesis measured. Single mature trifoliate leaves were exposed to photoinhibitory treatments at PFDs of 800 and 1400 μmol · m−2 · s−1 and at temperatures of 12 and 20°C. Chlorophyll fluorescence and photon yields were measured at regular intervals throughout each treatment. Plants grown in 13 h had significantly greater leaf areas than those grown in 8 h. There were no differences in maximum rates of photosynthesis, photon yields and only minor but significant differences in Fv/Fm for plants in the two treatments, showing photosynthetic characteristics were dependent on PFD but not DPR. A significant decline in photosynthesis and Fv/Fm occurred over the 13-h but little change in photosynthesis for plants in the 8 h, indicating some feedback inhibition of photosynthesis was occurring. Plants grown in 8 h were consistently more susceptible to photoinhibition of photosynthesis at all treatments than 13-h plants. Nevertheless, photoinhibition was exacerbated by increases in PFD, and by decreases in temperature for leaves from both treatments. However, for plants from the 8-h day, exposing leaves to 12°C and 1400 μmol · m−2 · s−1 caused photo-oxidation and severe bleaching but no visible damage on leaves from 13-h-grown plants. Closure of the photosystem II reaction-centre pool was partially correlated with increasing extents of photoinhibition but the relationship was similar for plants from both treatments. There remains no clear explanation for their wide differences in susceptibility to photoinhibition.

Growth and microbiology of nonmedicated, segregated, early-weaned pigs (1993)

Seventy pigs, 7 to 10 d of age, were randomly selected by litter of origin from a commercial farm in Northeast Kansas to compare the growth and microbiology of nonmedicated, segregated, early-weaned pigs to controls raised at the farm of origin. After weaning, both groups were fed a similar nutritional programs consisting of dry diets. No antimicrobial drugs were administered to the pigs except for a feed grade antimicrobial (carbadox) from weaning to 50 lb. Pigs were monitored for 12 weeks. Individual pigs weights, nasal swabs, and serum samples were collected on d 0 and then every 14 d thereafter for a total of 7 collections. Four pigs were necropsied at the initiation of the study (d 0). In addition, four pigs were randomly selected at each collection period from each group for necropsy and collection of tissues for bacterial culture. The segregated earlyweaned pigs were able to reach an accelerated phase of growth before the controls. On d 14, 28, 42, 56, and 70 of the experiment, segregated early-weaned pigs were 21, 82, 90, 54, and 52% heavier than control pigs, respectively. A low percentage of pigs were infected with Pasteurella multocida at 7 to 10 d of age, which corresponds to d 0 of the experiment. The principal time of transmission of P. multocida infection was in the immediate postweaning period. The rate of isolation of P. multocida then declined from d 14 to d 84 of the experiment in both groups of nonmedicated pigs. This response must be kept in mind when evaluating the efficacy of antibiotic protocols. Appropriate nonmedicated controls must also be evaluated. The maximum difference in rate of isolation of P. multocida from nasal swabs and tissues between the early and control groups occurred on d 28 and d 42 of the experiment. This corresponds to the two collection days when segregated early-weaned pigs were 82% and 90% heavier than control pigs raised on-site. The only Pasteurella multocida isolates capable of producing toxin were detected on d 14 in the control group. Pasteurella multocida toxin has also been shown to have deleterious effects on systemic organs and immune response. The rates of Bordetella bronchiseptica isolation were similar between control and segregated early-weaned groups. However, B. bronchiseptica isolates were recovered from any tissues of any pigs necropsied. Antibiotic regimens targeted at this organism would appear unwarranted in a commercial production setting. Haemophilus parasuis and Streptococcus suis were present in both groups of pigs at 7 to 10 d of age. However, as indicated by the excellent growth performance achieved in the presence of H. parasuis colonization of the nasal cavity, elimination of this organism probably is not necessary to achieve excellent growth levels. More studies need to be undertaken to understand the mode of transmission and epidemiology of Streptococcus suis infection. Mycoplasma hyopneumoniae apparently was eliminated without medication by moving pigs to an isolated site. Mycoplasma hyopneumoniae could be detected only in the control group. Data from this experiment also suggest that weaning pigs at 14 to 17 d could prevent vertical transmission of Actinobacillus pleuropneumonia. The growth and microbiology of nonmedicated, segregated, early-weaned pigs must be considered when developing cost-effective and efficacious medication protocols for application of segregated early weaning in the commercial swine industry.; Swine Day, Manhattan, KS, November 18,1993

Mitochondrial respiration in locust flight muscles

AbstractHighly coupled mitochondria isolated from locust flight muscles display substrate preferences consistent with the use of carbohydrate and lipid as the major metabolic fuels during flight. Maximal rates of coupled respiration expressed per milligram mitochondrial protein exceed by severalfold published values obtained using vertebrate muscle mitochondria. These differences in maximal rates of coupled respiration in vitro are apparent even when rates are expressed per unit mitochondrial marker enzyme (citrate synthase) activity or per unit mitochondrial volume (exchangeable water space). Locusts in flight achieve a greater fraction of the flux measured in vitro through cytochrome oxidase than mammals exercising at maximum aerobic capacity. These data suggest that besides possessing “better” mitochondria, locusts may possess higher capacities for O2 (and/or substrate) delivery, allowing the achievement of higher rates of respiration in vivo than in mammals. © 1992 Wiley‐Liss, Inc.

Respiration of Malate and Glutamate in SymbioticFrankiaPrepared fromAlnus incana

Frankia vesicle clusters were prepared from root nodules of Alnus incana (L.) Moench inoculated either with a local source of Frankia or with Frankia Cpll. The capacity of vesicle clusters to respire was investigated by respirometric and enzymological studies. Simultaneous addition of malate, glutamate, and NAD+ supported respiration in both types of Frankia, though at a smaller rate compared to the substrates NADH or 6-phosphogluconate. The saturating concentrations of malate and glutamate were also much higher than with the other substrates. No respiration was supported by succinate. Activity of the enzymes malate dehydrogenase (EC 1.1.1.37) and glutamate oxaloacetate transaminase (EC 2.6.1.1) was demonstrated in crude extracts from both types of symbiotic Frankia. Their maximum rates were high enough to account for the respiration of malate and glutamate. This respiration was inhibited by mersalylic acid, an inhibitor of the dicarboxylate shuttle in mitochondria, but it was shown that inhibition of respiration could be due to a direct effect on the enzymes. We conclude that respiration of malate and glutamate is most likely mediated by malate dehydrogenase and glutamate oxaloacetate transaminase, but no explicit evidence for or against the presence of a dicarboxylate carrier was found. The utilization of respiratory substrates was largely similar in the two types of Frankia, except for some differences in maximum rates and cofactor dependency.

Na +/K +/Cl −-cotransporter mediated Rb + fluxes in membrane vesicles from kidneys of normotensive and hypertensive rats

This paper describes experiments to examine Rb + fluxes via the Na +/K +/Cl − cotransporter in membrane vesicles from renal outer medulla of three strains of rat: (A) Wistar (B) Milan hypertensive (MHS) and normotensive (MNS), and (C) Sabra salt-sensitive hypertensive (SBH) and salt-resistant (SBN). Initially, Na +-dependent furosemide- or bumetanide-inhibited 86Rb + fluxes were characterised using Wistar rat microsomes. The latter were partially purified on a metrizamide cushion, and assay conditions were optimized for use with microsomes from the other rats. The major result is that in microsomes from adult Milan hypetensive (MHS) rats the rate of the Na +/K +/Cl −-cotransporter mediated 86Rb flux at sub-saturating concentrations of Rb, appears to be significantly greater than in the normotensive (MNS) controls. The effect reflects an increased apparent Rb affinity of the cotransporter in MHS microsomes. There is no difference in maximal rate or in the apparent Na + activation affinity of the 86Rb + flux. In addition bumetanide appears to be a somewhat more effective inhibitor in MHS compared to MNS microsomes. The 86Rb + flux result is compatible with a previous finding that in red cells, Na +/K +-cotransporter mediated fluxes are increased in MHS compared to MNS. It supports the notion that the Na +/K +/Cl −-cotransporter in both red cells and kidney is a genetic marker for hypertension. It is of interest that apparetly more than one Na + transport system is affected in MHS hypertensive kidneys (a) the Na +/K +/Cl − cotransporter i nthe thick ascending limb of Henle and (b) the Na +/H + exchanger and/or a conductive Na +-pathway in brush-border membranes from proximal tubule. It is conceivable that in the hypertensive animals a common regulatory pathway (e.g., phosphorylation) or protein (e.g., cytoskeleton) is affected along the length of the nephron. In Sabra SBH and SBN rat microsomes, no difference was found for the 86Rb + flux via the Na +/K +/Cl − cotransporter (or via a K + channel).

Modified reperfusate after long-term preservation of the heart

Warm (30 °C) blood cardioplegia (K = 22 mEq/L) with glutamate (26 mmol/L) as a reperfusate was compared with unmodified blood reperfusion after prolonged hypothermic storage of the isolated canine heart. After cardioplegic arrest, three groups of hearts (n = 5 each) were excised and stored at 2 °C. In groups 1 and 2, reperfusion with unmodified blood was undertaken after six and 24 hours of storage, respectively, and in group 3, reperfusion with modified warm blood cardioplegia containing glutamate was administered after 24 hours of storage. After reperfusion, no significant difference in left ventricular developed pressure was noted between groups 1 (110 ± 15 mm Hg), 2 (127 ± 14 mm Hg), and 3 (98 ± 13 mm Hg). Similarly, no difference in maximum rate of rise of left ventricular pressure was noted between groups 1 (1,456 ± 171 mm Hg/s), 2 (1,905 ± 395 mm Hg/ s), and 3 (1,450 ± 291 mm Hg/s). Group 3 (modified reperfusate) had improved diastolic compliance compared with group 2 (0.776 mm Hg/mL versus 1.395 mm Hg/mL; p < 0.02). We conclude that our modified reperfusate improves diastolic function after 24 hours of hypothermic storage, but does not result in improved systolic function.

METABOLIC REGULATION OF AMMONIUM UPTAKE BY ULVA RIGIDA (CHLOROPHYTA): A COMPARTMENTAL ANALYSIS OF THE RATE-LIMITING STEP FOR UPTAKE

Non-linear time courses of ammonium (NH4+) depletion from the medium and internal accumulation of soluble nitrogen (N) in macroalgae imply that the rate-limiting step for ammonium uptake changes over time. We tested this hypothesis by measuring the time course of N accumulation in N-limited Ulva rigida C. Agardh. Total uptake was measured as removal of NH4+ from medium. Rates for the component processes (transport of NH4+ across the membrane = Rv assimilation of tissure NH4+ into soluble N compounds = Ra, assimilation of tissue NH4+ into soluble N compounds = Ra and incorporation of soluble N compounds into macromolecules = R1) were determined by measuring the rate of labelling of the major tissue N pools after the addition of 15N-ammonium. The results indicate that nitrogen-specific rates (mass N taken up / mass N present / unit time) are ranked in the order of Rt < Ra < R1 Absolute uptake rates (μmol N. mg dry wt−1. h−1) showed a different relationship. Membrane transport appears to be inhibited when NH4+ accumulates in the tissue. Maximum uptake rates occur when assimilation of NH4+ into soluble N compounds begins. Assimilation of NH4+ into soluble N compounds was initially faster than incorporation of soluble N compounds into macromolecules. Implications of rate limitations caused by differences in maximal rates and maximal pool sizes are discussed.

Kinetic Determination of Tantalum in the Presence of Niobium

The rates of the ligand substitution reactions of niobium and tantalum complexes involving oxalate, tartrate, citrate or nitrilotriacetate as an auxiliary complexing agent with 4-(2-pyridylazo) resorcinol have been studied spectrophotometrically in acidic media. In the citrate system at pH 5, the maximum difference in rate of substitution between the niobium and the tantalum complexes was achieved. Under the chosen conditions, where the total concentrations of citrate and 4-(2-pyridylazo)resorcinol are 2×10−2 and 1×10−4 mol dm−3 respectively, the absorbance change during the reaction progress can be kinetically separated for each metal ion and less reactive tantalum in the range 10−6–10−5 mol dm−3 can be determined by a logarithmic extrapolation method. In the determination of 5×10−6 mol dm−3 of tantalum, the presence of 5-fold amounts (by molarity) of niobium can be tolerated. The effects of 52 diverse ions were examined.

Adaptive variation in the mammalian respiratory system in relation to energetic demand: V. Limits to oxygen transport by the circulation

This paper addresses the question of whether the structures determining convective transport of O 2 in the circulation are matched to the functional capacity of the system under the rate limiting conditions of V̇ O 2 max. ‘Athletic’ dogs and ponies are compared to ‘normal’ goats and calves, providing a 2.5-fold difference in V̇ O 2 max between two size pairs. A higher cardiac output (Q̇) and a larger arteriovenous oxygen concentration difference ( Ca O 2 − C V O 2 ) each provide about half of the 2.5-fold difference in maximal rates of O 2 delivery by the circulation. The higher Q̇ values of the athletic species are the result of larger stroke volumes, while maximal heart frequencies are the same for species of the same size. The higher ( Ca O 2 − C V O 2 ) of the athletic species is primarily the result of a higher hemoglobin concentration. Thus both mechanisms is involve building more structure of the same basic building blockes (cardiac muscle and erythrocytes). Our results suggest that all four species operate close to their upper limit of convective transport of O 2 in the circulation at V̇ O 2 max. We also find a constant relationship between mechanical work rate of the left ventricle and the volume of mitochondria, indicating that the supply of ATP to cardiac muscle is matched to its energy consumption at V̇ O 2 max. We conclude that the amount of structure is matched to the functional capacity of the circulatory system for transporting O 2 at V̇ 2 max.