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Biomedical subjects

D G Smith

Publications and source records attributed to D G Smith.

At least 307 records · Page 17Linked to original sources
PubMed1977

Differences in pulmonary microvascular anatomy between Bufo marinus and Xenopus laevis.

1. Histological and corrosion-casting techniques have been used to provide a comparison of lung structure between a terrestrial load (Bufo marinus) and an aquatic one (Xenopus laevis). The pulmonary microvascular anatomy is distinctly different in these two species and both differ from classical descriptions of other anuran lungs. 2. In X. laevis large peribronchial vessels form a number of direct connections between the pulmonary artery and vein at the base of the lung. As a result of their location these vessels could easily function as respiratory bypasses or shunts. No similar connections were found in B. marinus lungs, nor have they been previously described for any other anuran amphibians. Possible respiratory implications of their presence in X. laevis are discussed. 3. The patterns of major vessel distribution are markedly different in the two species. Despite these differences the appearance of the respiratory capillary beds and their patterns of supply and drainage are surprisingly similar, suggesting that common design problems have been encountered in the evolution of both lung types. 4. The lungs of X. laevis have considerably less septal and lung wall smooth muscle than is the case in B. marinus. However, Xenopus lungs are generally thicker-walled and of more solid construction. The differences are discussed in terms of the widely different habitats of the two species.

Animals↗
PubMed1977

Use of 13C in biosynthetic studies. The labelling pattern in tenellin enriched from isotope-labelled acetate, methionine, and phenylalanine.

The biogenetic origin of the carbon atoms in tenellin has been established by adding 13C-enriched compounds to cultures of Beauveria bassiana, and determining the isotopic distribution in the metabolite by 13C nuclear magnetic resonance spectrometry. Tenellin is formed by condensation of an acetate-derived polyketide chain with a phenylpropanoid unit that may be phenylalanine. Alternate carbon atoms of the polyketide chain were labelled with sodium [1(-13C)]- and [2-(13C]-acetate; sodium [1,2-(13C)]acetate was incorporated as intact two-carbon units, the presence of which in tenellin was apparent from coupling between adjacent 13C-enriched carbons. Substituent methyl groups of the polyketide-derived alkenyl chain were labelled with L-[Me-13C]methionine. The labelling patterns from DL-[carboxy-13C]phenylalanine and DL-[alpha-13C]phenylalanine indicated a rearrangement of the propanoid component at some stage in the synthesis. The mass spectrum of tenellin from cultures administered L-[15N]phenylalanine showed isotopic enrichment similar to that obtained with 13C- or 14C-labelled phenylalanine. During incorporation of L-[carboxy-14C, beta-3H]phenylalanine 96% of the tritium label was lost, discounting the possibility of a 1,2-hydride shift during biosynthesis of the metabolite.

Acetates↗
PubMed1977

Biosynthesis of gibberellins in Gibberella fujikuroi. Gibberellin A47.

Two minor radioactive products in cultures of G. fujikuroi strain ACC917 supplemented with labeled gibberellin A4 have been identified as the 2alpha-hydroxy derivative, gibberellin A47, and the hydrate, gibberellin A2. In addition, evidence was obtained by combined gas chromatography--mass spectrometry for the formation of 3-O-acetylgibberellin A1,3-O-acetylgibberellin A3, and gibberellin A20 by the culture. The time course of gibberellin synthesis in defined and complex media, as well as changes in the relative amounts of radioactive gibberellins formed when [4C]gibberellin A4 was added to cultures at different ages, suggest that the composition of the gibberellin mixture produced is determined by the balance between synthesis and decay of key enzymes in the branching pathway.

Gibberella↗
PubMed1977

Oxygen exchange in a simulated trout gill secondary lamella.

The complex blood flow patterns occurring in a trout secondary lamella were computed from a theoretical electrical model consisting of a two-dimensional array of unitary resistances representing the blood channels of the lamella. Estimates of oxygen uptake from water to blood were made by means of the standard conductance equations for oxygen and values from the literature for blood and water PO2's in trout. The results were plotted as contour charts of blood and water PO2, O2 transfer, and blood flow. According to the results of various manipulations of this model, oxygen exchange across a given lamella will be largely unaffected by changes in the overall shape of the lamella. However, the model predicted that oxygen exchange would be greatly reduced if 1) the basal pillar cell channels were denied access to the respiratory water flow, 2) pillar cell contraction were to force blood into the larger-diameter marginal channels, or 3) the blood flow rate were to be increased, regardless of a concomitant increase in water flow. These predictions are discussed in terms of current theories of gas exchange in teleost gills.

Animals↗
PubMed1977

Sites of cholinergic vasoconstriction in trout gills.

Sites of cholinergic vasoconstriction were investigated in isolated saline-perfused holobranchs of trout (Salmo gairdneri and S. trutta). Acetylcholine (ACh) always increased overall branchial vascular resistance (BVR) and, in addition, decreased the proportion of the total inflow appearing at the outflow cannula from the efferent arch artery. Since this was observed in both constant pressure and constant flow situations, it was concluded that ACh exerted most of its effect at a site downstream from the secondary lamellae, probably at the bases of the efferent filament arteries. Prussian blue dye injections indicated that, in addition, ACh caused a marked reduction in flow to the distal halves of the filaments and that flow within the proximal secondary lamellae was restricted during ACh administration to the inner and outer marginal channels of the lamellae. The results are discussed in terms of recent findings concerning the vascular anatomy of teleost gills.

Acetylcholine↗
PubMed1976

The anatomy of the pulmonary vascular bed in the toad Bufo marinus.

1. The pulmonary vascular anatomy of the toad, Bufo marinus was studied by scanning electron microscopy of vascular corrosion casts and of tissues prepared for light microscopy. 2. The lung is divided by septa into three orders of alveoli. Arterial branches run in the septa and cannot be observed directly through the lung surface. 3. The capillary bed forms a meshwork over the lumenal surface of septa and lung walls. It is divided into longitudinal zones of arterial distribution; it is broken along primary septal margins into primary alveolar units; within alveoli, it is functionally divided by distortion over circum-alveolar smooth muscle bundles. 4. The capillaries form a network of tubes rather than a perforated sheet of vascular space. Capillary beds on either face of septa are interconnected through the septum. 5. There is no evidence of collateral ("bronchial") vessels or of anatomically definable shunt vessels. 6. Intrinsic pulmonary arterial branches have a muscular coat.

Animals↗
PubMed1976

The effect of sample attrition on the frequency distribution of blood pressure and genetic marker phenotypes representing a natural unselected community: Tecumseh, Michigan.

High significant differences in mean age, blood pressure and phenotype frequency distributions between the non-migrants and "emigrants" of a total unselected community sample were discovered. Use of the mean of BP scores collected from epidemiologic surveys over a period of time as an individual score allows sample attrition to produce both a genetically and demographically biased sample of a population intended to represent an unselected community of people. Multiple regression analyses estimated the contribution of an individual's age, genotype and mobility out of the sample to predicting blood pressure variation. Variation in blood pressure means among certain marker phenotype classes was greater in those who leave than in those who stay, but only the upper portion of the pressure distribution contributed to this relationship. A genetic-environment interaction is suggested.

Female↗
PubMed1976

Biosynthesis of bikaverin in Fusarium oxysporum. Use of 13C nuclear magnetic resonance with homonuclear 13C decoupling to locate adjacent 13C labels.

Bikaverin obtained by supplementing cultures of Fusarium oxysporum with singly and doubly 13C labeled acetate was enriched by approximately 0.5 atom percent with the 13C isotope. At this low enrichment 13C NMR spectra of samples labeled from (1-13C)- and (2-13C) acetate did not show, unequivocally, the pattern of isotopic incorporation. Small sample size, poor solubility and difficulties in the assignment of resonances also restricted the amount of information thacetate. The difficulty was overcome by using 13C homonuclear single-frequency decoupling in conjunction with 1H heteronuclear decoupling to locate bonded 13C-13C pairs. The carbon skeleton of bikaverin was shown to be biosynthesized entirely by condensation of acetate units and the pattern of assembly was established.

Acetates↗
PubMed1975

Toxicity of aerosol propellants in the respiratory and circulatory systems. VIII. Respiration and circulation in primates.

The low-pressure propellants influence predominantly the circulation, whereas the high pressure propellants affect the respiration in anesthetized monkeys. There are four groups according to the level of toxicity: Class 1, low-pressure propellants of high toxicity that cause tachycardia and hypotension; Class 2, low-pressure propellants of intermediate toxicity that influence either circulation or respiration or both; Class 3, high-pressure propellants of intermediate toxicity that cause bronchoconstriction; and Class 4, high-pressure propellants of low toxicity that do not influence respiration or circulation even when inhaled at levels of up to 20 percent concentration.

Aerosol Propellants↗