Classes of tissue hypoxia

We identify eight causes of tissue hypoxia, falling into three classes, A, B, and C, depending upon the effect on the critical mixed venous pO2 and the optimal oxygen consumption rate. The critical mixed venous pO2 is the value above which the oxygen consumption rate is optimal and independent of the mixed venous pO2 and below which the oxygen consumption rate decreases towards zero. Class A hypoxia: primary decrease in mixed venous pO2. Causes: 1) ischaemic hypoxia (decrease in cardiac output), 2) low-extractivity hypoxia (decrease in oxygen extraction tension, px). Class B hypoxia: primary increase in critical mixed venous pO2. Causes: 1) shunt hypoxia (increased a-v shunting), 2) dysperfusion hypoxia (increased diffusion length from erythrocytes to mitochondria and/or decreased total capillary endothelial diffusion area, e.g., tissue oedema, microembolism), 3) histotoxic hypoxia (inhibition of the cytochrome chain). Class C hypoxia: primary increase in optimal oxygen consumption rate. Causes: 1) uncoupling hypoxia (uncoupling of the ATP formation associated with O2 reduction), 2) hypermetabolic hypoxia (increased energy metabolism, e.g., due to hyperthermia).

Laparoscopic colorectal surgery--are we being honest with our patients?

PURPOSE

A survey was undertaken to assess the impact of laparoscopy on the practice of colorectal surgery.

METHODS

A total of 1,520 questionnaires were mailed to all members of the American Society of Colon and Rectal Surgeons; 635 (42 percent) surgeons responded, 50 percent, and indicated that one questionnaire represented their entire group practice.

RESULTS

Two hundred seventy-eight (47 percent) respondents currently perform laparoscopic colorectal surgery; 62 percent (171) use the laparoscope for < or = 20 percent of their bowel resections. Conversely, only 6 percent (16) use the laparoscope in over 50 percent of resections. The percentage of surgeons who perform various procedures were right colectomy, 78 percent; left colectomy, 57 percent; stoma creations, 52 percent; anterior resection, 44 percent; Hartmann's closure, 42 percent; abdominoperineal resection, 27 percent; rectopexy, 18 percent; and total colectomy, 14 percent. If the preoperative diagnosis is known to be carcinoma, 196 (71 percent) surgeons attempted laparoscopic colorectal surgery, but 55 percent of surgeons (108) operated only for early lesions and 35 percent (68) only for palliation. To enable the procedure to be laparoscopically performed, 87 percent (243) of surgeons stated that they have changed their practice to include routine use of ureteral stents (23 percent), preoperative colonoscopic marking of small lesions (40 percent), or intraoperative colonoscopy. Despite increased use of endoscopy, there were 18 patients in whom the wrong segment of colon was removed. Moreover, nine patients had early local recurrence after resection of colon cancer, nine had early local recurrence after rectal cancer resection, and five had early port-site recurrence. Although 255 (40 percent) surgeons surveyed would themselves undergo laparoscopic colorectal surgery for a rectal villous adenoma, only 38 (6 percent) would have a laparoscopic anterior resection for cancer.

CONCLUSIONS

Several important problems exist including early port-site recurrence and a dual surgical standard. Although many surgeons are eager to practice laparoscopic colorectal surgery on their patients with carcinoma, they are reluctant to have the new technique applied to themselves.

The new class II transposon Tn163 is plasmid-borne in two unrelated Rhizobium leguminosarum biovar viciae strains

Tn163 is a transposable element identified in Rhizobium leguminosarum bv. viciae by its high insertion rate into positive selection vectors. The 4.6 kb element was found in only one further R. leguminosarum bv. viciae strain out of 70 strains investigated. Both unrelated R. leguminosarum bv. viciae strains contained one copy of the transposable element, which was localized in plasmids native to these strains. DNA sequence analysis revealed three large open reading frames (ORFs) and 38 bp terminal inverted repeats. ORF1 encodes a putative protein of 990 amino acids displaying strong homologies to transposases of class II transposons. ORF2, transcribed in the opposite direction, codes for a protein of 213 amino acids which is highly homologous to DNA invertases and resolvases of class II transposons. Homology of ORF1 and ORF2 and the genetic structure of the element indicate that Tn163 can be classified as a class II transposon. It is the first example of a native transposon in the genus Rhizobium. ORF3, which was found not to be involved in the transposition process, encodes a putative protein (256 amino acids) of unknown function. During transposition Tn163 produced direct repeats of 5 bp, which is typical for transposons of the Tn3 family. However, one out of the ten insertion sites sequenced showed a 6 bp duplication of the target DNA; all duplicated sequences were A/T rich. Insertion of Tn163 into the sacB gene revealed two hot spots. Chromosomes of different R. leguminosarum bv. viciae strains were found to be highly refractory to the insertion of Tn163.

[Disordered peripapillary microcirculation in glaucoma patients]

To study the haemodynamics of the peripapillary choroid, perfusion pressure videoangiography (PVA) was performed in six healthy subjects and in seven patients with primary open-angle glaucoma (poag). In healthy subjects the peripapillary part of the choroid starts filling at distinctly lower ocular perfusion pressures than other parts of the choroid. The mean difference in perfusion pressure between peripapillary and perimacular filling was 13.6 mmHg in the six healthy subjects. A different filling pattern of the choroid was found in the seven glaucoma patients. The mean difference in perfusion pressure between the beginning of peripapillary and the beginning of perimacular perfusion of the choroid was found to be as small as 1.9 mmHg. That the filling of the peripapillary choroid observed by PVA in healthy subjects is found to start at lower perfusion pressures than in the other parts is explained by autoregulative dilatation of the peripapillary choroidal arterioles resulting from artificially raised intraocular pressure during the PVA examination. In the poag patients the peripapillary choroidal arterioles were dilated either insufficiently or not at all. The following conclusions are drawn: (1) The peripapillary choroid of healthy persons shows effective autoregulation securing the blood supply to the prelaminar part of the optic nerve. (2) In poag the peripapillary choroid has lost the capability of effective autoregulation.

[Replication of ColE 1-related plasmids at increased growth temperature depending on rom function]

The content of ColE 1-related plasmids increased about 4-6-fold after a temperature-shift from 30 to 42 degrees C (45 degrees C) if the rom-region of the plasmids was deleted. The copy number of rom(+)-plasmids did not change after the temperature shift. All rom(-)-plasmids tested in this study showed this plasmid amplification. The Rom-protein is capable of inhibiting plasmid replication by stabilization the initial reversible stage of the association of RNA I with the primer precursor RNA II. We suggest that the temperature-dependent enhancement of the copy number of rom(-)-plasmids is due to a destabilization of this initial phase of the RNA I-preprimer interaction at high temperatures which is suppressed by the Rom-protein in cells with rom(+)-plasmids.

[In-vitro plaque accumulation on different filling materials]

The influence of the surface roughness of dental filling materials as well as of specific properties of materials on plaque accumulation was to be tested in a comparative study for various materials (Degulor S, Amalcap SAS, Visio Dispers, Ketak-Fil, CuproDur, Harvard Cement) was to be tested in a comparative investigation. For this purpose, the different materials were placed in a Streptococcus mutans NCTC 10449 culture medium containing sucrose, and incubated for three days at 37 degree C. Following this, the specific accumulation of polysaccharides formed outside of cells (plaque) was subjected to gravimetric analysis. Filling materials that take a high polish (Degulor S, Amalcap SAS, Visio Dispers) accumulated only 25 to 50% as much plaque as did cements. Within the group of cements there were also differences (up to 40%) in spite of similar surface roughness. These differences are presumably due to properties specific to the materials. In preliminary examinations of the products named, antibacterial effects were registered in three cases (Degulor S, Harvard Cement and Cupro-Dur--inhibiting areola between 1 and 7.5 mm).

Excretion into the culture medium of a Bacillus beta-glucanase after overproduction in Escherichia coli

The beta-glucanase gene (bgl) from Bacillus amyloliquefaciens was expressed in E. coli CSH 55 under the control of the PR promoter of phage lambda that is repressed by the thermosensitive repressor C1857. Production of beta-glucanase was drastically stimulated by a temperature shift to 42 degrees C. This overexpression of the bgl gene (about 20% of the total cellular protein) led to an almost complete excretion of the otherwise periplasmic protein into the extracellular medium, beta-glucanase accounted for more than 50% of the extracellular proteins. Col E 1 related plasmid (pEG 1) are amplified in E. coli relA strains in response to an amino acid limitation leading to a 10-fold increase in the activity of plasmid encoded genes. In this work we intended to maximize the expression of the bgl gene by a concerted action of a plasmid amplification and temperature induction. Surprisingly we could not increase the beta-glucanase production above the level reached by plasmid amplification or temperature induction alone. The reasons for this unexpected result will be discussed. Under all conditions tested the expression of the bgl gene was much lower in the E. coli relA strain NF 162 than in E. coli CSH 55; the low beta-glucanase production was accompanied by a reduced excretion rate of the enzyme.

Apparatus for the electrical characterisation of conductive fluids

Non-invasive and fully automated conductimetric measurements of electrolyte and bacterial samples were achieved in a closed volume test cell, comprising a magnetic field coil and detector. By monitoring field induced currents in sample electrolytes the magnitude of the sample current was shown to vary as the inverse of the sample impedance. The impedance characteristic was shown to be that of an LCR resonant circuit. This characteristic is primarily a function of the applied frequency and the solution/cell properties being dependent on the solution conductivity and dielectric permittivity at any given concentration. Small changes in sample dielectric permittivity in the presence of a large background conductivity are shown to be significant. The apparatus described can provide fixed or swept frequency conductivity measurements in the range 1 kHz to 2.25 MHz with a lower conductivity sensitivity of 0.9 x 10(-3) Scm-1. Bulk impedimetric characteristics of cell suspensions are derived by a two stage measurement.

A mutant insulin receptor with defective tyrosine kinase displays no biologic activity and does not undergo endocytosis

The cDNAs encoding the normal human insulin receptor (HIRc) and a receptor that had lysine residue 1018 replaced by alanine (A/K1018) were used to transfect Rat 1 fibroblasts. Lysine 1018 is a critical residue in the ATP binding site of the tyrosine kinase domain in the receptor beta-subunit. Untransfected Rat 1 cells express 1700 endogenous insulin receptors. Expressed HIRc receptors had levels of insulin-stimulable autophosphorylation in vitro comparable to normal receptors, whereas A/K1018 receptors had less than 1% of that activity. Stimulation by insulin of HIRc receptors in situ in intact cells led to phosphorylation of beta-subunit tyrosine residues and activation of tyrosine kinase activity that could be preserved and assayed in vitro after receptor purification. In contrast, A/K1018 receptors showed no such activation, either of autophosphorylation or of kinase activity toward histone. Cells expressing HIRc receptors display enhanced sensitivity to insulin of 2-deoxyglucose transport and glycogen synthase activity. This increased sensitivity was proportional to insulin receptor number at low but not at high levels of receptor expression. A/K1018 receptors were unable to mediate these biologic effects and actually inhibited insulin's ability to stimulate glucose transport and glycogen synthase through the endogenous Rat 1 receptors. Expressed HIRc receptors mediated insulin internalization and degradation, whereas A/K1018 receptors mediated little, if any. Endocytotic uptake of the expressed A/K1018 insulin receptors was also markedly depressed compared to normal receptors. Unlike HIRc receptors, A/K1018 receptors also fail to undergo down-regulation after long (24 h) exposures to high (170 nM) concentrations of insulin. We conclude the following. 1) Normal human insulin receptors expressed in Rat 1 fibroblasts display active tyrosine-specific kinase, normal intracellular itinerary after endocytosis, and normal coupling to insulin's biologic effects. 2) A receptor mutated to alter the ATP binding site in the tyrosine kinase domain had little if any tyrosine kinase activity. 3) This loss of kinase activity was accompanied by a nearly complete lack of both endocytosis and biologic activity.

Effects of magnesium deficiency on the photosynthesis and respiration of leaves of sugar beet

The effects of Mg deficiency on the photosynthesis and respiration of sugar beets (Beta vulgaris L. cv. F58-554H1) were studied by withholding Mg from the culture solution and by following changes in CO(2) and water vapor exchange of attached leaves. Leaf blade Mg concentration decreased from about 1200 to less than 200 meq kg(-1) dry matter without change in the rate of photosynthetic CO(2) uptake per unit leaf area, while from 200 to 50 meq kg(-1) the rate decreased to one-third. Rates of photorespiratory evolution of CO(2) into CO(2)-free air responded to Mg like those of photosynthetic CO(2) uptake, the rates decreasing to one-half, below 200 meq kg(-1). Respiratory CO(2) evolution in the dark increased almost 2-fold in low Mg leaves. Magnesium deficiency had less effect on leaf (mainly stomatal) diffusion resistance (r(1)) than on mesophyll resistance (r(m)); in Mg-deficient plants r(m) increased from 2.9 to 7.1 sec cm(-1), whereas r(1) became significantly greater than the control value only in the most severe instances of Mg deficiency.

Effects of Potassium Deficiency on the Photosynthesis and Respiration of Leaves of Sugar Beet under Conditions of Low Sodium Supply

Sugar beet plants (Beta vulgaris L. cv. F58-554H1) were germinated and cultured under standardized environmental conditions. The effects of K deficiency on photosynthetic and respiratory CO(2) exchange rates of attached leaves were studied under conditions of low Na supply by withholding both Na and K from the culture medium at cut-off (28 days after planting). Potassium and Na concentrations in the leaf blade and petiole decreased rapidly during the 8 days after cut-off, then more slowly.Photosynthetic CO(2) uptake per unit leaf area decreased rapidly with time after cut-off to 23% of the control rate in 17 days. Mesophyll resistance to CO(2) (r(m)) increased sharply after cut-off, r(m) eventually attaining 8.3 sec cm(-1). Leaf (mainly stomatal) diffusion resistance, r(1)', also increased rapidly from 4 days after cut-off, reaching 1.9 sec cm(-1) 13 days later. The photorespiratory evolution of CO(2) into CO(2)-free air decreased progressively after cut-off, but the rate of dark respiratory CO(2) evolution increased. It was concluded that withholding Na as well as K at cut-off increased the deleterious effects of K deficiency on photosynthesis and stomatal opening.

Effects of potassium deficiency on the photosynthesis and respiration of leaves of sugar beet

Sugar beet plants (Beta vulgaris L. var. F5855441) were germinated and cultured under standardized environmental conditions for 28 days. Potassium deficiency was then induced by withholding K from the culture solution. Changes in CO(2) and water vapor exchange rates and surface temperatures of individual attached leaves were measured with time after K cut-off, along with changes in the concentrations of the leaf minerals K, Na, Ca, Mg, Fe, Mn, Cu, and Zn. During the 1st week after K cut-off the concentration of Na in the leaf blade increased from 200 to 1000 milliequivalents per kilogram dry matter while K decreased from 1500 to 300 milliequivalents per kilogram. During the subsequent 2 weeks, both Na and K concentrations decreased. The concentrations of other leaf minerals, except Mn, were little affected by K cut-off. Photosynthetic CO(2) uptake per unit area decreased linearly with time after cut-off and attained one-third of the control rate after 21 days. Low K apparently decreased photosynthesis through an increase in mesophyll resistance to CO(2) (r(m)) from 2.8 to 5.3 seconds per centimeter in 21 days. Leaf (mainly stomatal) diffusion resistance (r'(1)) increased only slowly during the first 15 days from 0.3 to 0.5 second per centimeter, eventually reaching 1.6 seconds per centimeter at 21 days. Low K progressively decreased the photorespiratory evolution of CO(2) into CO(2)-free air, but steadily increased the rate of CO(2) evolution in dark.

Effects of phosphorus deficiency on the photosynthesis and respiration of leaves of sugar beet

Phosphorus deficiency was induced in sugar beet plants (Beta vulgaris L. var. F5855441), cultured hydroponically under standardized environmental conditions, by removal of phosphorus from the nutrient supply at the ten leaf stage 28 days after germination. CO(2) and water vapor exchange rates of individual attached leaves were determined at intervals after P cutoff. Leaves grown with an adequate nutrient supply attained net rates of photosynthetic CO(2) fixation of 125 ng CO(2) cm(-2) sec(-1) at saturating irradiance, 25 C, and an ambient CO(2) concentration of about 250 mul l(-1). After P cutoff, leaf phosphorus concentrations decreased as did net rates of photosynthetic CO(2) uptake, photorespiratory evolution of CO(2) into CO(2)-free air, and dark respiration, so that 30 days after cutoff these rates were about one-third of the control rates. The decrease in photosynthetic rates during the first 15 days after cutoff was associated with increased mesophyll resistance (r(m)) which increased from 2.4 to 4.9 sec cm(-1), while from 15 to 30 days there was an increase in leaf (mainly stomatal) diffusion resistance (r(l)') from 0.3 to 0.9 sec cm(-1), as well as further increases in r(m) to 8.5 sec cm(-1). Leaf diffusion resistance (r(l)') was increased greatly by low P at low but not at high irradiance, r(l)' for plants at low P reaching values as high as 9 sec cm(-1).

Potassium Deficiency-induced Changes in Stomatal Behavior, Leaf Water Potentials, and Root System Permeability in Beta vulgaris L

Studies of the water relations of potassium deficient sugarbeet plants (Beta vulgaris L.) revealed two factors for stomatal closure. One component of stomatal closure was reversible by floating leaf discs on distilled water to relieve the water deficit in the leaves; the other component was reversible in the light by floating the leaf discs on KCl solution for 1 hour or more. Potassium-activated stomatal opening in the light was observed when the guard cells were surrounded by their normal environment of epidermal and mesophyll cells, just as observed by previous workers for epidermal strips. Leaf water potentials, like stomatal apertures, appear to be strongly related to leaf potassium concentration. Potassium-deficient plants have a greatly decreased root permeability to water, and the implications of this effect on stomatal aperture and leaf water potential are discussed. In contrast, petiole permeability to water is unaffected by potassium treatment.

Effects of moisture stress on the multiplication and expansion of cells in leaves of sugar beet

Sugar beets were subjected to moisture stress by decreasing the water potential of the culture solution osmotically with polyethylene glycol by a known amount, ΔΨ π , and, alternatively by applying matric potential, Ψ τ , at the plant roots. Lowering the water potential at the root surface less than 200 millibars by either method resulted in significant decreases in the rate of cell multiplication. The final number of cells per leaf at Ψ π = -372 mb the final was 165% of that at Ψ π = -473 mb (ΔΨ τ = -101 mb); similarly at Ψ τ = -15 mb the final cell number was 198% of that at Ψ τ = -196 mb (ΔΨ τ = -181 mb). The mean cell volume of leaves was not significantly affected by these levels of moisture stress.

Sodium absorption by intact sugar beet plants

Sodium absorption by intact sugar beet plants (Beta vulgaris) was found to be mediated by at least two distinct mechanisms when uptake was studied over a wide range of Na and K concentrations. The first mechanism operates at low Na concentrations (<1 milliequivalent per liter); presence of K completely blocks this mechanism for Na. The second mechanism operates at high Na concentrations (>1 milliequivalent per liter), transporting Na as well as K; but apparently this mechanism is not active for Na absorption in young sugar beet plants up to the 10-leaf stage.