Relationships between blood pressure and heart rate in the saltwater crocodile Crocodylus porosus

The cardiac limb of the baroreflex loop was studied in the saltwater crocodile Crocodylus porosus, The classical pharmacological methodology using phenylephrine and sodium nitroprusside was used to trigger blood pressure changes, and the resulting alterations in heart rate were analysed quantitatively using a logistic function. Interindividual differences in resting heart rates and blood pressures were observed, but all seven animals displayed clear baroreflex responses. Atropine and sotalol greatly attenuated the response. A maximal baroreflex gain of 7.2 beats min(-1) kPa(-1) was found at a mean aortic pressure of 6.1 kPa, indicating the active role of the baroreflex in a wide pressure range encompassing hypotensive and hypertensive states. At the lowest mean aortic pressures (5.0 kPa), the synergistic role of the pulmonary-to-systemic shunt in buffering the blood pressure drop also contributes to blood pressure regulation, Pulse pressure showed a better correlation,vith heart rate and also a higher gain than mean aortic, systolic or diastolic pressures, and this is taken as an indicator of the existence of a differential control element working simultaneously with a linear proportional element.

Human vascular to cardiac tissue selectivity of L- and T-type calcium channel antagonists

1 Voltage-operated calcium channel (VOCC) antagonists are effective antihypertensive and antianginal agents but they also depress myocardial contractility. 2 We compared four L-type calcium channel antagonists, felodipine, nifedipine, amlodipine and verapamil and a relatively T-type selective calcium channel antagonist, mibefradil, on human and rat isolated tissue assays to determine their functional vascular to cardiac tissue selectivity (V/C) ratio. 3 The V/C ratio was calculated as the ratio of the IC50 value of the antagonist that reduced (by 50%) submaximally contracted (K+ 62 mM) human small arteries from the aortic vasa vasorum (vascular, V) mounted in a myograph and the IC50 value of the antagonist that reduced (-)-isoprenaline (6 nM) submaximally stimulated human right atrial trabeculae muscle (cardiac, C) mounted in organ chambers. 4 The average pIC(50) Values (-log IC50 M) for the human vascular preparations were felodipine 8.30, nifedipine 7.78, amlodipine 6.64, verapamil 6.26 and mibefradil 6.22. The average pIC(50) values for the cardiac muscle were felodipine 7.21, nifedipine 6.95, verapamil 6.91, amlodipine 5.94, and mibefradil 4.61. 5 The V/C ratio calculated as antilog [pIC(50)V-pIC(50)C] is thus mibefradil 41, felodipine 12, nifedipine 7, amlodipine 5 and verapamil 0.2. 6 In rat small mesenteric arteries the pIC(50) values for the five drugs were similar to the values for human vasa vasorum arteries contracted by K+ 62 mM. However for methoxamine (10 mu M) contraction in the rat arteries the pIC(50) values were lower for felodipine 7.24 and nifedipine 6.23, but similar for verapamil 6.13, amlodipine 6.28 and mibefradil 5.91. 7 In conclusion in the human tissue assays, the putative T-channel antagonist mibefradil shows the highest vascular to cardiac selectivity ratio; some 3 fold higher than the dihydropyridine, felodipine, and some 200 fold more vascular selective than the phenylalkylamine, verapamil. This favourable vascular to cardiac selectivity for mibefradil, from a new chemical class of VOCC antagonist, may be explained by its putative T-channel selectivity.

Unsupervised cell nucleus segmentation with active contours

The task of segmenting cell nuclei from cytoplasm in conventional Papanicolaou (Pap) stained cervical cell images is a classical image analysis problem which may prove to be crucial to the development of successful systems which automate the analysis of Pap smears for detection of cancer of the cervix. Although simple thresholding techniques will extract the nucleus in some cases, accurate unsupervised segmentation of very large image databases is elusive. Conventional active contour models as introduced by Kass, Witkin and Terzopoulos (1988) offer a number of advantages in this application, but suffer from the well-known drawbacks of initialisation and minimisation. Here we show that a Viterbi search-based dual active contour algorithm is able to overcome many of these problems and achieve over 99% accurate segmentation on a database of 20 130 Pap stained cell images. (C) 1998 Elsevier Science B.V. All rights reserved.

The velocity of probability transport in quantum mechanics

In his study of the 'time of arrival' problem in the nonrelativistic quantum mechanics of a single particle, Allcock [1] noted that the direction of the probability flux vector is not necessarily the same as that of the mean momentum of a wave packet, even when the packet is composed entirely of plane waves with a common direction of momentum. Packets can be constructed, for example for a particle moving under a constant force, in which probability flows for a finite time in the opposite direction to the momentum. A similar phenomenon occurs for the Dirac electron. The maximum amount of probabilitiy backflow which can occur over a given time interval can be calculated in each case.

Insufficiently active Australian college students: Perceived personal, social, and environmental influences

Background. A sustainable pattern of participation in physical activity is important in the maintenance of health and prevention of disease, College students are in transition from an active youth to a more sedentary adult behavior pattern. Methods. We assessed self-reported physical activity and other characteristics in a sample of 2,729 male and female students (median age was 20 years) recruited from representative courses and year levels at four Australian College campuses. They were categorized as sufficiently or insufficiently active, using estimates of energy expenditure (kcal/week) derived from self-reported physical activity, Personal factors (self-efficacy, job status, enjoyment), social factors (social support from family/friends), and environmental factors (awareness of facilities, gym membership) were also assessed. Results. Forty-seven percent of females and 32% of males were insufficiently active. For females, the significant independent predictors of being insufficiently active were lower social support from family and friends, lower enjoyment of activity, and not working. For males, predictors were lower social support from family and friends, lower enjoyment of activity, and being older. Conclusions. Factors associated with physical activity participation (particularly social support from family and friends) can inform physical activity strategies directed at young adults in the college setting. (C) 1999 American Health Foundation and Academic Press.

Two-wave-mixing induced self-focusing in an active photorefractive oscillator

We derive a nonlinear wave equation for a signal beam which is coupled to a pump beam by two-wave-mixing in a photorefractive crystal. This equation describes self-focusing of the signal beam. We compare two-wave-mixing induced spatial self-focusing of single-pass experiments in a diffusion-type photorefractive crystal and of a photorefractive oscillator using the same crystal. We observe that the nonlinear refractive index change in the oscillator is decreased while increasing resonator losses.

Both CD4(+) and CD8(+) lymphocytes reduce the severity of tissue lesions in murine systemic candidiasis, and CD4(+) cells also demonstrate strain-specific immunopathological effects

The role of T lymphocytes in host responses to sublethal systemic infection with Candida albicans was evaluated by mAb depletion of CD4(+) and CD8(+) cells from BALB/c and CBA/CaH mice, which develop mild and severe tissue damage, respectively. Depletion of CD4(+) lymphocytes from BALB/c mice markedly increased tissue damage, but did not alter the course of infection. In CBA/CaH mice, depletion of CD4+ cells abrogated tissue destruction in both brain and kidney at day 4 after infection, and significantly decreased fungal colonization in the brain. However, the severity of tissue lesions increased relative to controls from day 8 onwards. A small increase in tissue damage was evident in both mouse strains after depletion of CD8(+) cells. There were no major differences between days 4 end 8 after infection in cDNA cytokine profiles of CD4(+) lymphocytes from either BALB/c or CBA/CaH mice. After passive transfer into infected syngeneic recipients, spleen cells from infected CBA/CaH mice markedly increased tissue damage when compared to controls, and also caused a significant increase in fungal colonization in the brain. A similar transfer in BALB/c mice increased the number of inflammatory cells in and around the lesions, but had no effect on the fungal burden in brain and kidney. The data demonstrate that both CD4(+) and CD8(+) lymphocytes contribute to the reduction of tissue damage after systemic infection with C. albicans, and that the development and expression of CD4(+) lymphocyte effector function is influenced by the genetic background of the mouse.

The crack tip strain field of AISI 4340 - Part II - Experimental measurements

Crack tip strain maps have been measured for AISI 4340 high strength steel. No significant creep was observed. The measured values of CTOD were greater than expected from the HRR model. Crack tip branching was observed in every experiment. The direction of crack branching was in the same direction as a major ridge'' of epsilon(yy) strain, which in turn was in the same direction as predicted by the HRR model. Furthermore, the measured magnitudes of the epsilon(y)y strain in this same direction were in general greater than the values predicted by the HRR model. This indicates more plasticity in the crack tip region than expected from the HRR model. This greater plasticity could be related to the larger than expected CTOD values. The following discrepancies between the measured strain fields for AISI 4340 and the HRR predictions are noteworthy: (1) The crack branching. (2) Values of CTOD significantly higher than predicted by HRR. (3) The major ridge'' of epsilon(yy) strain an angle of about 60 degrees with the direction of overall propagation of the fatigue precrack, in which the measured magnitudes of the epsilon(yy) strain were greater than the values predicted by the HRR model. (4) Asymmetric shape of the plastic zone as measured by the epsilon(yy) strain. (5) Values of shear strain gamma(xy) significantly higher than predicted by the HRR model. (C) 1999 Kluwer Academic Publishers.

The crack tip strain field of AISI 4340 - Part III - Hydrogen influence

This paper studied the influence of hydrogen and water vapour environments on the plastic behaviour in the vicinity of the crack tip for AISI 4340. Hydrogen and water vapour (at a pressure of 15 Torr) significantly increased the crack tip opening displacement. The crack tip strain distribution in 15 Torr hydrogen was significantly different to that measured in vacuum. In the presence of sufficient hydrogen, the plastic zone was larger, was elongated in the direction of crack propagation and moreover there was significant creep. These observations support the hydrogen enhanced localised plasticity model for hydrogen embrittlement in this steel. The strain distribution in the presence of water vapour also suggests that SCC in AISI 4340 occurs via the hydrogen enhanced localised plasticity mechanism. (C) 1999 Kluwer Academic Publishers.

Comparison of acetylcholinesterase genes from cattle ticks

We describe the isolation and characterisation of two putatively new acetylcholinesterase genes from the African cattle ticks Boophilus decoloratus and Rhipicephalus appendiculatus. The nucleotide sequences of these genes had 93% homology to each other and 95% and 91% identity, respectively, to the acetylcholinesterase gene from an Australian strain of another cattle tick, Boophilus microplus. Translation of the nucleotide sequences revealed putative amino acids that are essential for acetylcholinesterase activity: the active site serine, and the histidine and glutamate residues that associate with this serine to form the catalytic triad. All known acetylcholinesterases have three sets of cysteines that form disulfide bonds; however, the acetylcholinesterase genes of these three species of ticks encode only two sets of cysteines. Acetylcholinesterases of B. microplus from South Africa, Zimbabwe, Kenya and Mexico had 98-99% identity with acetylcholinesterase from B. microplus from Australia, whereas acetylcholinesterase from B. microplus from Indonesia was identical to that from Australia. Preliminary phylogenetic analyses surprisingly indicate that the acetylcholinesterases of ticks are closer phylogenetically to acetylcholinesterases of vertebrates than they are to those of other arthropods. (C) 1999 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.

Active site-directed protein regulation

Regulation of protein function is vital for the control of cellular processes. Proteins are often regulated by allosteric mechanisms, in which effecters bind to regulatory sites distinct from the active sites and alter protein function. Intrasteric regulation, directed at the active site and thus the counterpart of allosteric control, is now emerging as an important regulatory mechanism.

Novel murine myeloid cell lines that exhibit a differentiation switch in response to IL-3 or GM-CSF, or to different constitutively active mutants of the CM-CSF receptor beta subunit

Several activating mutations have recently been described in the common beta subunit for the human interleukin(IL)-3, IL-5, and granulocyte-macrophage colony-stimulating factor (GM-CSF) receptors (h beta c), Two of these, FI Delta and 1374N, result, respectively, in a 37-amino acid duplication and an isoleucine-to-asparagine substitution in the extracellular domain. A third, V449E, leads to valine-to-glutamic acid substitution in the transmembrane domain. Previous studies have shown that when expressed in murine hemopoietic cells in vitro, the extracellular mutants can confer factor independence on only the granulocyte-macrophage lineage while the transmembrane mutant can do so to all cell types of the myeloid and erythroid compartments. To further study the signaling properties of the constitutively active hpc mutants, we have used novel murine hemopoietic cell lines, which we describe in this report. These lines, FDB1 and FDB2, proliferate in murine IL-3 and undergo granulocyte-macrophage differentiation in response to murine GM-CSF, We find that while the transmembrane mutant, V449E, confers factor-independent proliferation on these cell lines, the extracellular hpc mutants promote differentiation. Hence, in addition to their ability to confer factor independence on distinct cell types, transmembrane and extracellular activated h beta c mutants deliver distinct signals to the same cell type. Thus, the FDB cell lines, in combination with activated h beta c mutants, constitute a powerful new system to distinguish between signals that determine hemopoietic proliferation or differentiation. (C) 2000 by The American Society of Hematology.

The biologically active iron chelators 2-pyridylcarboxaldehyde isonicotinoylhydrazone, 2-pyridylcarboxaldehyde benzoylhydrazone monohydrate and 2-furaldehyde isonicotinoylhydrazone

In the crystal structures of the respective title compounds, C12H10N4O, C13H11N3O . H2O and C11K9N3O2, variations in the torsion angles of the aromatic pyridyl and benzoyl groups are observed, and the disposition of the heterocyclic aldehyde is shown to be influenced by the ring size of this group.