Hypoxia-induced inhibition of converting enzyme activity: role in vascular regulation

Systemic and pulmonary vascular reactivity to graded doses of angiotensin I (ANG I), angiotensin II (ANG II), and, as a control, phenylephrine were examined in 14- or 28-day hypoxia-exposed and air control rats. Hypoxic rats exhibited pulmonary hypertension that was reversible on return to room air, but systemic arterial pressure was not altered by hypoxia. Systemic pressor responses to ANG I and ANG II were significantly less in the hypoxic rats than in the control rats at 14 and 28 days but returned to control levels in hypoxic animals that were then returned to room air, demonstrating reversibility of the hypoxia-induced changes in vascular reactivity. Pulmonary pressor responses to ANG I were significantly less at 14 days, whereas responses to ANG II were significantly greater at 28 days, in hypoxic rats than in controls. There were no significant differences in systemic and pulmonary pressor responses to phenylephrine between the hypoxic and air control animals. The altered systemic and pulmonary pressor responsiveness to ANG I and ANG II in hypoxic rats is probably related to mechanisms specific to the renin-angiotensin system, such as inhibition of intrapulmonary angiotensin-converting enzyme activity and down regulation of ANG II receptors in the systemic circulation. Further study is needed to elucidate these mechanisms.     

Molecular genotyping of human T-cell antigen receptor variable gene segments

The gene complex encoding the chain of the T-cell antigen receptor (Tcr) in man was previously reported to contain a restriction fragment length polymorphism (RFLP) involving a single Bgl II site adjacent to the second constant region gene. This RFLP allowed assignment of Tcr genotypes in certain human families. In the present study, two different RFLP in a V gene family were detected using the murine probe V8.1 in genomic DNA samples digested with the restriction endonucleases Hind III and Bam HI. Use of these RFLP to mark the V gene complex allowed complete haplotype assignment in four of seven families studied and provided support for linkage of the V gene complex to the constant region genes. Different combinations of the C and two V region markers can result in eight possible distinct haplotypes. The observation of all but one of the eight possible haplotypes in parents of the families studied suggests that recombination events occur between the C and V region and among members of the V region subfamily marked by the V8.1 probe. These markers can be used for mapping studies of the V gene complex in man and will allow an appraisal of possible associations between Tcr genes and disease susceptibility.Abbreviations used in this paper: Tcr T-cell antigen receptor - RFLP restriction fragment length polymorphism - C2 second Tcr constant region gene - V Variable - C constant - J joining - D diversity     

The nutritional ecology of the ctenophore Bolinopsis vitrea: comparisons with Mnemiopsis mccradyi from the same region

Bolinopsis vitrea is a warm water lobate ctenophore which doesnot overlap in its distribution with Mnemiopsis mccradyi incontiguous waters. We examined its feeding ecology on a seriesof cruises. B. virrea ingested increasingly more prey at higherfood concentrations (2–100 prey l^–1) but feedingeffort (clearance rate) decreased with increasing food availability.On a dry weight basis, smaller tentaculate Bolinopsis ingestedseveral times more than larger lobates, but based on carbonweight, specific ingestion was fairly uniform over the entiresize range investigated (6–60 mm total length). Bolinopsiscollected during the daytime in the Bahamas rarely had morethan three prey items in their guts. These results and laboratorymeasurements of digestion times (av. = 1.9 h) allowed computationof daily rations, which could not account for the metabolicrequirement as measured on the same cruises. Results of feedingexperiments, however, implied that prey densities in excessof 11^–1 were sufficient to sustain a growing populationof Bolinopsis. Prey concentrations about an order of magnitudehigher were required for M. mccradyi based on similar experiments.These results were in general agreement with observed densitiesand distributions of ctenophores and their zooplankton preyin the Bahamas and coastal South Florida.     

Photosynthetic pathways in a midwestern rock outcrop succulent,Sedum nuttallianum Raf. (Crassulaceae)

Shoots of Sedum nuttallianum exhibited CAM^* acid fluctuations in the field. These nocturnal acid accumulations persisted in the laboratory under well-watered and water-stressed conditions. Simultaneous measurements of transpiration, however, indicated daytime stomatal opening and nocturnal stomatal closure. Measurements of CO₂ and H₂O vapor exchange continuously for six days after watering substantiated these results in part: the majority of CO₂ uptake occurred during the day early in the experiment; however, after several days without water, nighttime CO₂ uptake was stimulated and eventually was greater than the drastically reduced daytime CO₂ uptake. This nighttime uptake was never quite sufficient to account for all estimated increases in tissue acidity. Thus, a combination of CAM and CAM-cycling occurred early in the desiccation experiment. Evidence for CAM and a form of CAM-idling was found later in the experiment. Though nighttime CO₂ uptake occurred and persisted after only one day without water, rates were too low to alter the tissue ¹³C/¹²C value from a C₃-like number (–30). Thus, although CAM and CAM-idling may have survival value during extended droughts, shoots of S. nuttallianum apparently utilize the C₃ pathway to obtain most of their carbon.Abbreviations C₃ pathway - CO₂ fixation pathway in which an intermediate containing 3 carbon atoms is formed - CAM Crassulacean acid metabolism - Chl Chlorophyll - c_i internal CO₂ concentration - DW Dry weight - g_c mean conductance to CO₂ - FW Fresh weight - PAR Photosynthetically active radiation - SD Standard deviation - vpd Vapor pressure deficit - WUE Water use efficiency     

Human alpha- and beta-CGRP and rat alpha-CGRP are coronary vasodilators in the rat

The effects of the recently described human alpha-calcitonin gene-related peptide (CGRP), human beta-CGRP and rat alpha-CGRP have been compared with those of the vasodilator sodium nitroprusside, on the rat and rabbit isolated heart. Hearts were perfused at constant flow and [Arg8]-vasopressin was used to increase coronary perfusion pressure. In the rat heart, the order of potency for evoking cumulative dose-dependent falls in perfusion pressure was human beta-CGRP greater than rat alpha-CGRP greater than human alpha-CGRP greater than sodium nitroprusside. In the same preparations the three CGRPs (but not sodium nitroprusside) elicited cumulative dose-related increases in heart rate. In the rabbit heart the order of potency for vasodilatation was rat alpha-CGRP greater than human alpha-CGRP greater than sodium nitroprusside. In marked contrast to results from the rat, neither rat alpha-CGRP nor human alpha-CGRP altered heart rate in the rabbit isolated heart. These results show that human alpha- and beta-CGRP and rat alpha-CGRP are vasodilators in the coronary vasculature, but that there is species variation as CGRP had a positive chronotropic effect in the rat heart but not in the rabbit heart.     

Chemolithotrophic metabolism of the newly-isolated moderately thermophilic,obligately autotrophic Thiobacillus tepidarius

Thiobacillus tepidarius, isolated from the hot springs at Bath, Avon, UK, grew optimally at 43–45°C and pH 6.0–7.5 on thiosulphate or tetrathionate. In batch culture, thiosulphate was oxidized stoichiometrically to tetrathionate, with a rise in pH. The tetrathionate was then oxidized to sulphate, supporting growth and producing a fall in pH to a minimum of ph 4.8. The organism contained high levels of thiosulphate-oxidizing enzyme, rhodanese and ribulose bisphosphate carboxylase. It was obligately chemolithotrophic and autotrophic. In chemostat culture, T. tepidarius grew autotrophically with the following sole energy-substrates: sulphide, thiosulphate, trithionate, tetrathionate, hexathionate or heptathionate. Thiocyanate, dithionate and sulphite were not used as sole substrates, although sulphite enhanced growth yields in the presence of thiosulphate. Maximum specific growth rate on tetrathionate was 0.44 h^-1. True growth yields (Y _max) and maintenance coefficients (m) were calculated for sulphide, thiosulphate, trithionate and tetrathionate and observed yields at a single fixed dilution rate compared with those on hexathionate and heptathionate. Mean values for Y _max, determined from measurements of absorbance, dry wt, total organic carbon and cell protein, were similar for sulphide, thiosulphate and trithionate (10.9 g dry wt/mol substrate) as expected from their equivalent oxygen consumption for oxidation. Y _max for tetrathionate (20.5) and the relative Y _o values (as g dry wt/g atom oxygen consumed) for thiosulphate and all four polythionates indicated that substrate level phosphorylation did not contribute significantly to energy conservation. These Y _max values were 40–70% higher than any of those previously reported for obligately aerobic thiobacilli. Mean values for m were 6.7 mmol substrate oxidized/g dry wt·h for sulphide, thiosulphate and trithionate, and 2.6 for tetrathionate.Abbreviation PIPES Piperazine-N,N-bis(ethane sulphonic acid)     

Assembly of microfibrils in vivo and in vitro from (1»3)-β-d-glucan synthesized by protoplasts of Saccharomyces cerevisiae

Polymer chains of (13)--d-glucan were dissolved with 1 M NaOH at 4° C from native microfibrillar protoplast nets. The chains associated into microfibrils during NaOH neutralization or dialysis. In contrast to the native microfibrils which are of uniform width individually (10 to 20 nm) and arranged in flat bundles, the microfibrils formed in vitro showed no band formation and consisted of fibrous spindle-shaped subunits of variable width or loose elementary fibrils about 1.7 nm wide. X-ray diagrams of native nets indicated a fairly high crystallinity and were different for wet and dry specimens. They corresponded to those of paramylon. Precipitated glucans produced diagrams different from the former and revealing a lower crystallinity especially with the dry samples.The X-ray pattern, combined with other data, allowed the precipitated microfibrils to be identified as aggregates of molecular strands composed each of three intertwined helical glucan chains. Since these triple helical chains are about 1.7 nm wide the elementary fibrils of this width can represent only single triple-helical strands. These helices have 7 glucose residues per turn and therefore a low symmetry which explains the poor crystallizing properties. The 7 membered helix represents a basic difference with the well crystallized native glucan which is built of highly symmetrical triple helices with 6 glucose residues per turn. Since 6₁ helical conformation is not formed in vitro at normal temperatures its generation in vivo must be due to the action of synthesizing enzymes at the protoplast membrane. The intertwining of these helices and crystallization of the strands are determined by their symmetry and physical properties of the chains. This characterizes the native microfibrils as products of self-assembly of enzymegenerated 6₁ helices.     

Iron-Chelating Compounds Produced by Soil Pseudomonads: Correlation with Fungal Growth Inhibition

Strains of Pseudomonas putida, Pseudomonas sp., and Pseudomonas aeruginosa were examined for their ability to grow in the presence of the iron chelator, ethylenediamine-di-(o-hydroxyphenylacetic acid). In vitro fungal inhibition assays showed that the isolates varied in their ability to inhibit the growth of representative fungal plant pathogens. Fungal inhibition in vitro was superior to that of previously reported Pseudomonas sp. Studies with Fusarium oxysporum forma sp. lycopersici and a susceptible tomato cultivar demonstrated that Pseudomonas putida PPU3.1 was able to significantly reduce wilt disease.