Diaphragmatic blood flow in the dog

In anesthetized mongrel dogs we measured the blood flow in the left phrenic artery (Qdi), using an electromagnetic flow probe, before and during supramaximal phrenic nerve stimulation (pacing). This was done at constant respiratory rate (24/min) but at three different stimulation frequencies at a duty cycle of 0.4 (20, 50, and 100 Hz) and at three different duty cycles at a stimulation frequency of 50 Hz (duty cycle = 0.2, 0.4, and 0.8). Qdi was unchanged during diaphragm contraction until transdiaphragmatic pressure (Pdi) was greater than approximately 11 cmH2O, whereafter it began to decrease, reaching zero at Pdi approximately 20 cmH2O. Thus, when Pdi was greater than 21 cmH2O, all flow occurred during relaxation. Qdi averaged over the entire respiratory cycle (Qt) was less at duty cycle = 0.8 than under the other conditions. This was because of decreasing length of relaxation phase rather than a difference of relaxation phase flow (Qr), which was maximal during all conditions of phrenic stimulation. During pacing-induced fatigue, Qt actually rose slightly as Pdi fell. This was due to an increase in contraction phase flow while Qr remained constant. The relationship between Qt and tension-time index was not unique but varied according to the different combinations of duty cycle and stimulus frequency.     

Studies on ciliated protozoa in eutrophic lakes: 2. Field and laboratory studies on the effects of oxygen and other chemical gradients on ciliate distribution

An investigation into the spatial distribution of hypolimnetic ciliates in three small eutrophic lakes during the period of summer stratification was carried out. Peak ciliate densities were found to occur at the oxic/anoxic boundary, ciliate numbers declining with increasing depth within the hypolimnion. The ciliates only occurred in aerobic water where oxygen levels were less than about 0.5 mgl^–1 Laboratory experiments demonstrated that the ciliates swim upwards under anaerobic conditions but swim rapidly downwards under aerobic conditions. Further laboratory experiments showed that although the bulk of the population occured within anaerobic water, the hypolimnetic ciliates are aerobes and cannot survive indefinite anoxia. Despite the demonstrable toxicity of high levels of ammonia and sulphide, it was probably excesive distance from an available source of oxygen that excluded the ciliates from the lowest levels of the hypolimnion. Possible mechanisms which allowed these aerobic ciliates to colonise anaerobic water are considered.     

Valveless pumping behavior of the simulated embryonic heart tube as a function of contractile patterns and myocardial stiffness

Biomechanics and Modeling in Mechanobiology - During development, the heart begins pumping as a valveless multilayered tube capable of driving blood flow throughout the embryonic vasculature. The...     

Comparative genome analysis of potential regulatory elements in the ABCG5-ABCG8 gene cluster

The excretion of sterols from the liver and intestine is regulated by the ABCG5 and ABCG8 transporters. To identify potential regulatory elements, 152 kb of the human ABCG5-ABCG8 gene cluster was sequenced and comparative genome analysis was performed. The two genes are oriented in a head-to-head configuration and are separated by a 374-bp intergenic region, which is highly conserved among several species. Using a reporter construct, the intergenic region was found to act as a bidirectional promoter. A conserved GATA site in the intergenic region was shown by site-directed mutagenesis to act as a repressor for the ABCG5 promoter. The intergenic region was also shown to be partially responsive to treatment by LXR agonists. In summary, several potential regulatory elements were found for the ABCG5 and ABCG8 genes, and the intergenic region was found to act as a bidirectional promoter.     

Differential recovery of peptides from sample tubes and the reproducibility of quantitative proteomic data

Differential recovery of peptides due to nonspecific adsorption can seriously compromise reproducibility and quality of proteomic data for peptide analyses by liquid chromatography-mass spectrometry (LC-MS). This study demonstrates large variations in reproducibility and quantitation of LC-MS data for peptides derived from tryptic digests of BSA upon storage in different sample tubes. Notably, we show that highly improved consistency and lower errors in quantitation of BSA tryptic peptides in replicate measurements is achieved with low-retention tubes compared to regular eppendorf tubes. Furthermore, qualitative differences in peptides detected by LC-MS were observed in the two types of storage tubes. These results illustrate the necessity for careful evaluation of storage vessels and conditions to minimize variability in sample quality for LC-MS experiments.     

Folding into a beta-hairpin can prevent amyloid fibril formation

The tetrapeptide KFFE is one of the shortest amyloid fibril-forming peptides described. Herein, we have investigated how the structural environment of this motif affects polymerization. Using a turn motif (YNGK) or a less rigid sequence (AAAK) to fuse two KFFE tetrapeptides, we show by several biophysical methods that the amyloidogenic properties are strongly dependent on the structural environment. The dodecapeptide KFFEAAAKKFFE forms abundant thick fibril bundles. Freshly dissolved KFFEAAAKKFFE is monomeric and shows mainly disordered secondary structure, as evidenced by circular dichroism, NMR spectroscopy, hydrogen/deuterium exchange measurements, and molecular modeling studies. In sharp contrast, the dodecapeptide KFFEYNGKKFFE does not form fibrils but folds into a stable beta-hairpin. This structure can oligomerize into a stable 12-mer and multiples thereof, as shown by size exclusion chromatography, sedimentation analysis, and electrospray mass spectrometry. These data indicate that the structural context in which a potential fibril forming sequence is present can prevent fibril formation by favoring self-limiting oligomerization over polymerization.     

Experimental investigation of the success of stocked, domestic brown trout and their effects on wild brown trout in upland and lowland rivers

The stocking of adult, domestic brown trout (DBT)( Salmo trutta L.) to supplement angling catches is a common practice. There is increasing concern, however, over the effects of such stockings on indigenous wild brown trout (WBT) populations. This paper describes an experimental field trial to explore the success of stocked DBT and their effects on WBT growth and abundance. DBT adults were stocked into upland rain‐fed and lowland spring‐fed streams. Three stocking treatments and a control were replicated six times for each of the two stream categories. In spring, baseline adult (defined as >200 mm LF) WBT densities were increased by 25, 50 and 100% using equal quantities of two different strains of DBT from two large suppliers. All DBT were measured, weighed and tagged before being stocked. The stocking procedure approximated to current stocking practice. A total of 48 500 m experimental sites were used. The abundance of WBT was estimated at each survey site in the summer prior to stocking via electrofishing and the depletion method. All WBT captured were measured and weighed. In addition, all WBT >100 mm were tagged. Habitat was assessed using the HABSCORE model. Post‐treatment monitoring was undertaken in the summer following stocking. Data will be presented regarding the effects of the stocking treatments on the growth and abundance of WBT as well as the strain‐dependent performance of DBT across all sites and on a river type‐specific basis. The suitability of using HABSCORE to formulate appropriate stocking densities will be discussed.     

Studies on non-steroidal inhibitors of aromatase enzyme; 4-(aryl/heteroaryl)-2-(pyrimidin-2-yl)thiazole derivatives

Steroidal and non-steroidal aromatase inhibitors target the suppression of estrogen biosynthesis in the treatment of breast cancer. Researchers have increasingly focused on developing non-steroidal derivatives for their potential clinical use avoiding steroidal side-effects.Non-steroidal derivatives generally have planar aromatic structures attached to the azole ring system. One part of this ring system comprises functional groups that inhibit aromatization through the coordination of the haem group of the aromatase enzyme. Replacement of the triazole ring system and development of aromatic/cyclic structures of the side chain can increase selectivity over aromatase enzyme inhibition.In this study, 4-(aryl/heteroaryl)-2-(pyrimidin-2-yl)thiazole derivatives were synthesized and physical analyses and structural determination studies were performed. The IC₅₀ values were determined by a fluorescence-based aromatase inhibition assay and compound 1 (4-(2-hydroxyphenyl)-2-(pyrimidine-2-yl)thiazole) were found potent inhibitor of enzyme (IC₅₀:0.42?nM). Then, their antiproliferative activity over MCF-7 and HEK-293 cell lines was evaluated using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Compounds 1, 7, 8, 13, 15, 18, 21 were active against MCF-7 breast cancer cells. Lastly, a series of docking experiments were undertaken to analyze the crystal structure of human placental aromatase and identify the possible interactions between the most active structure and the active site.     

Detecting low-abundance vasoactive peptides in plasma: Progress toward absolute quantitation using nano liquid chromatography-mass spectrometry

Profiling changes in the concentration of functionally related peptide hormones is critical to understanding the etiology of many diseases and therapies. We present novel data using nano liquid chromatography-mass spectrometry (LC-MS) to simultaneously measure a select group of vasoactive peptides (angiotensin, bradykinin, and related hormones) in 50-μl plasma samples, enabling repeated sampling in rodent models. By chromatographically resolving target peptides and using multiple reaction monitoring to enhance MS sensitivity, linear responses down to 10⁻¹⁷ mol were achieved. Purification of plasma peptides by either methanol precipitation or off-line high-performance liquid chromatography (HPLC) fractionation enabled the detection of endogenous peptides and revealed approaches for enhancing recovery. As proof of principle, seven vasoactive peptides were profiled before, during, and after acute angiotensin-converting enzyme (ACE) inhibition in an anesthetized rat. Of note was an apparent 10-fold increase in vasodilatory bradykinin that reversed after drug infusion but relatively minor changes in angiotensin II levels. Targeted MS analysis used to profile functionally related peptides or other analytes will greatly enhance our ability to define the sequence of events regulating complex and dynamic physiological processes.