Pasteurella challenge and ELISA serology evaluation of broiler breeders vaccinated with live cholera vaccine

A novel high-pressure, high-resolution NMR probe is described which operates at a frequency of 500 MHz. The design features an alternative RF coil (8 mm sample tube) for high frequency, sensitivity, probe power, and resolution (< 3.0 x 10(-9)). The probe is capable of pressures to at least 5 kbar over a temperature range of -30 to 80 degreesC, and has a double-tuned 1H/2H circuit which can tune at 1H frequencies of either 300 or 500 MHz. The sensitivity of the 300-MHz circuit is over twice that of previous 10-mm high-pressure NMR probe designs, while at 500 MHz the sensitivity is nearly five times that of previous 300-MHz pressure probes. Potential biochemical applications are demonstrated by 2D NOESY spectra of a Troponin C mutant.     

Three-dimensional hysterosonography for the study of endometrial tumors: comparison with conventional transvaginal sonography, hysterosalpingography, and hysteroscopy

The combined effects of pressure and temperature on the activity of butyrylcholinesterase (BuChE) were investigated in the pressure range from 10(-3) to 5 kbar and temperature range from -10 degrees C to 70 degrees C. Inactivation of the enzyme showed a complex dependence on pressure and temperature. Under moderate pressures (1-3 kbar) at temperatures 40-65 degrees C BuChE was resistant to heat inactivation; under other conditions of pressure and temperature, the action of both parameters was synergistic and caused inactivation. Results allowed to construct a pressure-temperature kinetic phase diagram for the enzyme inactivation. The elliptic diagram for the irreversible transition active-->inactive BuChE as a function of both pressure and temperature has a positive angular coefficient. This indicates that pressure acts as a stabilizer of BuChE against heat denaturation.     

The unusually slow unfolding rate causes the high stability of pyrrolidone carboxyl peptidase from a hyperthermophile, Pyrococcus furiosus: equilibrium and kinetic studies of guanidine hydrochloride-induced unfolding and refolding

To elucidate the energetic features of the anomalously high-level stabilization of a hyperthermophile pyrrolidone carboxyl peptidase (PfPCP) from a hyperthermophilic archaeon, Pyrococcus furiosus, equilibrium and kinetic studies of the guanidine hydrochloride (GuHCl)-induced unfolding and refolding were carried out with CD measurements at 220 nm in comparison with those from the mesophile homologue (BaPCP) from Bacillus amyloliquefaciens. The mutant protein of PfPCP substituted with Ser at both Cys142 and Cys188 (PfC142/188S) was used. The GuHCl unfolding for PfC142/188S and BaPCP was reversible. It was difficult to obtain the equilibrated unfolding curve of the hyperthermophile proteins at temperatures below 50 degreesC and pH 7, because of the remarkably slow rate of the unfolding. The unfolding for PfC142/188S attained equilibrium after 7 days at 60 degreesC, resulting in the coincidence between the unfolding and refolding curves. The Gibbs energy change of unfolding, DeltaGH2O (56.6 kJ/mol), for PfC142/188S at 60 degreesC and pH 7 was dramatically higher than that (7.6 kJ/mol) for BaPCP at 40 degreesC and pH 7. The unfolding and refolding kinetics for PfC142/188S and BaPCP at both 25 and 60 degreesC at pH 7 were approximated as a single exponential. The rate constant in water (kuH2O) of the unfolding reaction for PfC142/188S (1.6 x 10(-)15 s-1) at 25 degreesC and pH 7 was drastically reduced by 7 orders of magnitude compared to that (1.5 x 10(-)8 s-1) for BaPCP, whereas the refolding rates (krH2O) in water for PfC142/188S (9.3 x 10(-)2 s-1) and BaPCP (3.6 x 10(-)1 s-1) at 25 degreesC and pH 7 were similar. These results indicate that the greater stability of the hyperthermophile PCP was characterized by the drastically slow unfolding rate.     

The H-phosphonate approach to the solution phase synthesis of linear and cyclic oligoribonucleotides

The solution phase synthesis of the tetraribonucleoside triphosphate r(ApCpGpU) 18 and the corresponding cyclic tetraribonucleotide 19 is described. The synthetic methodology is based on 5'- O -(DMTr)-2'- O -(Fpmp)-ribonucleoside-3'- H -phosphonate building blocks 10. Coupling, which is rapid and quantitative, is effected with di-(2-chlorophenyl) phosphorochloridate 5 at -40 degreesC; it is followed by in situ treatment with 2-(4-methyl-phenyl)sulphanyl-1 H -isoindole-1,3(2 H )-dione 6b. The resulting sulphur transfer reaction also proceeds rapidly and quantitatively at -40 degreesC. The same coupling and sulphur transfer steps are used in the cyclization reaction, but a 5'- H -phosphonate intermediate 24 is involved. The final three-step unblocking process involves treatment with (i) E -2-nitrobenzaldoxime 7 and N 1, N 1, N 3, N 3-tetramethylguanidine (TMG) 8 in aceto-nitrile, (ii) concentrated aqueous ammonia at 50 degreesC and (iii) 0.5 mol/dm3sodium acetate buffer (pH 4.0) at 40 degreesC. The fully unblocked products 18 and 19 were characterized by NMR spectroscopy and by enzymatic digestion.     

An unusual oxygen-sensitive, iron- and zinc-containing alcohol dehydrogenase from the hyperthermophilic archaeon Pyrococcus furiosus

Pyrococcus furiosus is a hyperthermophilic archaeon that grows optimally at 100 degreesC by the fermentation of peptides and carbohydrates to produce acetate, CO2, and H2, together with minor amounts of ethanol. The organism also generates H2S in the presence of elemental sulfur (S0). Cell extracts contained NADP-dependent alcohol dehydrogenase activity (0.2 to 0.5 U/mg) with ethanol as the substrate, the specific activity of which was comparable in cells grown with and without S0. The enzyme was purified by multistep column chromatography. It has a subunit molecular weight of 48,000 +/- 1,000, appears to be a homohexamer, and contains iron ( approximately 1.0 g-atom/subunit) and zinc ( approximately 1.0 g-atom/subunit) as determined by chemical analysis and plasma emission spectroscopy. Neither other metals nor acid-labile sulfur was detected. Analysis using electron paramagnetic resonance spectroscopy indicated that the iron was present as low-spin Fe(II). The enzyme is oxygen sensitive and has a half-life in air of about 1 h at 23 degreesC. It is stable under anaerobic conditions even at high temperature, with half-lives at 85 and 95 degreesC of 160 and 7 h, respectively. The optimum pH for ethanol oxidation was between 9. 4 and 10.2 (at 80 degreesC), and the apparent Kms (at 80 degreesC) for ethanol, acetaldehyde, NADP, and NAD were 29.4, 0.17, 0.071, and 20 mM, respectively. P. furiosus alcohol dehydrogenase utilizes a range of alcohols and aldehydes, including ethanol, 2-phenylethanol, tryptophol, 1,3-propanediol, acetaldehyde, phenylacetaldehyde, and methyl glyoxal. Kinetic analyses indicated a marked preference for catalyzing aldehyde reduction with NADPH as the electron donor. Accordingly, the proposed physiological role of this unusual alcohol dehydrogenase is in the production of alcohols. This reaction simultaneously disposes of excess reducing equivalents and removes toxic aldehydes, both of which are products of fermentation.     

An extracellular protease of Streptococcus gordonii hydrolyzes type IV collagen and collagen analogues

Streptococcus gordonii is a frequent cause of infective bacterial endocarditis, but its mechanisms of virulence are not well defined. In this study, streptococcal proteases were recovered from spent chemically defined medium (CDM) and fractionated by ammonium sulfate precipitation and by ion-exchange and gel filtration column chromatography. Three proteases were distinguished by their different solubilities in ammonium sulfate and their specificities for synthetic peptides. One of the enzymes cleaved collagen analogs Gly-Pro 4-methoxy-beta-naphthylamide, 2-furanacryloyl-Leu-Gly-Pro-Ala (FALGPA), and p-phenylazobenzyloxycarbonyl-Pro-Leu-Gly-Pro-Arg (pZ-peptide) and was released from the streptococci while complexed to peptidoglycan fragments. Treatment of this protease with mutanolysin reduced its 180- to 200-kDa mass to 98 kDa without loss of enzymatic activity. The purified protease cleaved bovine gelatin, human placental type IV collagen, and the Aalpha chain of fibrinogen but not albumin, fibronectin, laminin, or myosin. Enzyme activity was inhibited by phenylmethylsulfonyl fluoride, indicating that it is a serine-type protease. Maximum production of the 98-kDa protease occurred during growth of S. gordonii CH1 in CDM containing 0.075% total amino acids at pH 7.0 with minimal aeration. Higher initial concentrations of amino acids prevented the release of the protease without reducing cell-associated enzyme levels, and the addition of an amino acid mixture to an actively secreting culture stopped further enzyme release. The purified protease was stored frozen at -20 degreesC for several months or heated at 50 degreesC for 10 min without loss of activity. These data indicate that S. gordonii produces an extracellular gelatinase/type IV collagenase during growth in medium containing minimal concentrations of free amino acids. Thus, the extracellular enzyme is a potential virulence factor in the amino acid-stringent, thrombotic, valvular lesions of bacterial endocarditis.     

Thermal recovery in 304 stainless steel following explosive shock loading and explosive forming

The annealing behavior of type 304 stainless steel sheet samples shock-loaded at pressures between 750 and 1200 kbar, and cylindrical samples explosively expanded between 32 and 62 pct is characterized by rapid (catastrophic) hardness recovery between 750° and 850°C. Apparent aging effects, the occurrence of precipitates and dislocation loops of varying sizes, and a preferential etching at grain boundaries in thin electropolished foils is observed at 750 and 1200 kbar and 32 and 62 pct. Electron transmission microscope observations revealed that the catastrophic recovery and subsequent pseudorecrystallization were essentially synonymous, with no apparent nucleation and growth of new grains. Recovery is characterized mainly by the collapse of deformation twins and the accelerated annihilation of dislocations. Considerably less recovery is observed for lower shock pressures (<750 kbar), and for less explosive expansion (<25 pct) as evidenced by the presence of numerous dislocations at temperatures where complete recovery has occurred for higher pressure samples. It is suggested that a nonequilibrium vacancy concentration exists at the higher shock-pressures and larger degrees of explosive expansion, and that this feature is largely strain-rate dependent.     

Cryopreservation of unfertilized mouse oocytes: the effect of replacing sodium with choline in the freezing medium

Although embryo cryopreservation has become commonplace in many species, effective methods are not available for routine freezing of unfertilized eggs. Cryopreservation-induced damage may be caused by the high concentration of sodium ions in conventional freezing media. This study investigates the effect of a newly developed low-sodium choline-based medium (CJ2) on the ability of unfertilized, metaphase II mouse eggs to survive cryopreservation and develop to the blastocyst stage in vitro. Specifically, the effects of cooling to subzero temperatures, thawing rate, LN2 plunge temperature, and equilibration with a low-sodium medium prior to freezing are examined. In contrast to cooling to 23, 0, or -7.0 degreesC in a sodium-based freezing medium (ETFM), cooling in CJ2 had no significant negative effect on oocyte survival or development. Oocytes frozen in CJ2 survived plunging into LN2 from -10, -20, or -33 degreesC at significantly higher rates than oocytes frozen in ETFM. With the protocol used (1.5 M PrOH, 0.1 M sucrose, -0.3 C/min, plunging at -33 degreesC) rapid thawing by direct submersion in 30 degreesC water was more detrimental to oocyte survival than holding in air for 30 or 120 s prior to transfer to water. Equilibration of unfertilized oocytes with a low-sodium medium prior to cryopreservation in CJ2 significantly increased survival and blastocyst development. These results demonstrate that the high concentration of sodium in conventional freezing media is detrimental to oocyte cryopreservation and show that choline is a promising replacement. Reducing the sodium content of the freezing medium to a very low level or eliminating sodium altogether may allow oocytes and other cells to be frozen more effectively.     

Low-dose midazolam attenuates predatory odor avoidance in rats

Based on the premise that optimal drug delivery might improve the efficacy of locoregional treatment for solid tumors, the authors set up an experimental model for isolation perfusion in surgical specimens from patients resected for carcinoma of the colon. Ten surgical specimens were cannulated, washed internally and externally with saline solution, promptly cooled to 4 degreesC, connected to a circuit, and perfused with Krebs-Henselait modified solution, concentrated red blood cells, albumin, desamethasone, glucose, and heparin for 60 minutes at a target temperature of 37 degreesC. Organ temperature, flow rate, perfusion pressure, and metabolic and functional parameters were checked at 5, 20, and 60 minutes of perfusion. A paraphysiologic perfusion procedure was achieved. Mean values (and ranges) were as follows: temperature 37 degreesC (35. 1-39.6 degreesC); flow rate 10.2 (5.6-17.9) ml/min/100 g; arterial pressure 96 (42-154) mmHg; arterial pH 7.3 (7.1-7.5); arterial PO2 183 (78-304) mmHg; arterial PCO2 36 (31-46) mmHg. No important signs of tissue damage were found at histology. Autonomous or stimulated peristalsis (or both) was present throughout the experiment. Mean O2 extraction was 7.9 ml/min/100 g (range 3.1-11.0). Mean glucose consumption was 229 mg/100 g (range 174-252). The model worked well and appears promising, particularly for future use in various pharmacokinetic and pharmacodynamic studies of antiblastic agents.     

Existence of a mannitol hydrate during freeze-drying and practical implications

We report thermal and crystallographic evidence for a previously unknown mannitol hydrate that is formed in the process of freeze-drying. The mannitol hydrate was produced by freeze-drying pure mannitol solutions (1-4% w/v) using the following cycle: (1) equilibration at -5 degreesC for 1 h; (2) freezing at -40 degreesC; (3) primary drying at -10 degreesC for 15 h; and (4) secondary drying at 10 degreesC for 2 h and then 25 degreesC for 5 h. This crystal form was also observed upon freeze-drying in the presence of sorbitol (1% w/v). The mannitol hydrate showed a distinct X-ray powder diffraction pattern, low melting point, and steplike desolvation behavior that is characteristic of crystalline hydrates. The mannitol hydrate was found to be metastable, converting to anhydrous polymorphs of mannitol upon heating and exposure to moisture. The amount of the mannitol hydrate varied significantly from vial to vial, even within the same batch. The formation of mannitol hydrate has several potential consequences: (1) reduced drying rate; (2) redistribution of the residual hydrate water during accelerated storage to the amorphous drug; and (3) vial-to-vial variation of the moisture level.     

Activation of angiotensin II-forming chymase in the cardiomyopathic hamster heart

Thermoluminescence (TL) emission arising from charge recombination in photosynthetic reaction centres was examined considering the energy transfer between antenna chlorophylls and the reaction centre. The energy transfer processes were shown to decrease the width and change the temperature of the maximum glow of the TL band profiles when the rate constant of direct recombination between the oxidized primary electron donor and reduced primary acceptor (pheophytin or bacteriopheophytin) did not exceed 10(6) s-1. The primary radical pair lifetime of 3.10(-9)-10(-8) s was shown to minimize the influence of energy transfer on the TL band profiles and, therefore, the energy transfer can be neglected when the TL band profiles are calculated. The profile of the TL band arising from charge recombination in the photosystem 2 state S2QB.- was shown to depend considerably on the temperature-dependent rate constant of direct recombination between QB.- and S2 state of the photosystem 2 donor site.     

Survival of frozen-thawed human red cells as a function of cooling and warming velocities

Human red cells were equilibrated for 30 min at 20degreesC in buffered saline containing 2 M glycerol and then frozen to --196degreesC at 0.27, 1.7, 59, 180, 480, 600, and 1300degreesC/min and warmed at 0.47, 1, 26, 160, and 550degreesC/min. Cells frozen at 600 and 1300degreesC/min responded in the classical fashion for cells containing intracellular ice; i.e., survivals were low when warming was slow (less than 10%), but increased progressively with increasing warming rate. The sensitivity to slow warming presumably reflects the recrystallization of intracellular ice. Cells frozen at 59 and 180degreesC/min yielded high survivals at all warming rates. This response is also consistent with the findings for other cells cooled just slowly enough to preclude intracellular ice. Cells frozen very slowly at 0.27 and 1.7degreesC/min, however, responded differently; survivals were considerably higher when warming was slow (0.47 or 1degreesC/min) than when it was 26, 160, or 550degreesC/min. This response is analogous to that observed recently by others in mouse embryos and in higher plant tissue-culture cells and to that observed for many years in higher plants. It also confirms previous observations of Meryman in human red cells. It may reflect osmotic shock from rapid dilution but, if so, the basis of the osmotic shock is uncertain.     

Chlorination kinetics of ZnO with Ar-Cl2-O2 gas and the effect of oxychloride formation

The chlorination rate of ZnO with Ar-Cl₂-O₂ gas was measured from 1023 K to 1273 K and the effects of temperature and partial pressures of chlorine and oxygen were investigated. The rate-determining step of chlorination was considered to be the dissociation of intermediate between ZnO and Cl₂ from linear relationship between reciprocal values of reaction rate and partial pressure of chlorine. The activation energy of chlorination was 58.2±2.5 kJ/mol. This comparatively low activation energy as a chemically controlled reaction was consistent with estimated rate-determining step of the dissociation of unstable compound. Increasing the partial pressure of oxygen slightly increased the chlorination rate, and this effect is considered to be caused by the increase in the formation rate of zinc oxychloride. To clarify the formation of zinc oxychloride, the equilibrium between Ar-Cl₂-O₂ gas and ZnO was investigated by the transpiration method at 1073 K. Calculated partial pressures of ZnOCl from experimental results were in the same order with or one order of magnitude larger than those estimated from reported Gibbs energy of formation of ZnOCl. Zinc oxychloride formation in ZnO chlorination must be taken into consideration as well as ZnCl₂ and Zn₂Cl₄ formation.     

The role of the house fly (Musca domestica) in the dissemination of hookworm

The effect of cooling rate, warming rate, and duration of phase transition upon survival of frozen canine kidneys was investigated. In the present study, 11 kidneys out of 14 rapidly cooled (2--4degreesC/min) to --22degreesC and thawed (70--110degreesC/min) were viable following contralateral nephrectomy. The serum creatinine and BUN levels rose to a maximum of 8.4 and 30 mg%, respectively, on the eighth day post-contralateral nephrectomy. Average survival time was 10 days; however, two of the dogs in this group were allowed to survive, one for 3 months and one for over 2 years. Eight kidneys out of 16 slowly cooled (0.25-1.0degreesC/min) and either rapidly or slowly warmed (20-30degreesC/min) had function to produce small amounts of urine; however, they did not survive more than 5 days after contralateral nephrectomy. Cooling rates of 0.1 and 10degreesC/min were too harmful to the kidney to have renal function after reimplantation. The minimum renal cell damage as assessed by LDH and GOT in the post-freeze perfusate was found in the 2-4degreesC/min cooling rate following rapid warming (70degrees-110degreesC/min). Correlation of the duration of phase transition time to renal cell damage was linear for LDH and GOT (r=0.93). This result suggests that the duration of phase transition time also is an important factor during the freezing process, affecting post-thaw survival of canine kidneys.     

Conversion of temperature-sensitive to -resistant gene expression due to mutations in the promoter region of the melibiose operon in Escherichia coli

The melibiose utilization system of Escherichia coli W3133, a derivative of K12, is nonfunctional between 37 and 42 degreesC. The reason for this temperature sensitivity was thought to be that the melibiose transporter (MelB) of W3133 cells was temperature-sensitive. A mutant W3133-2 has been isolated as a temperature-resistant strain that can utilize melibiose between 37 and 42 degreesC. However, we found that the melibiose transporter of the W3133-2 was still temperature-sensitive. Half-life activities of the melibiose transporter at 37 degreesC (or 40 degreesC) in both E. coli W3133 and W3133-2 were exactly the same. Furthermore, we found that the nucleotide sequence of coding region of the melB structural gene (the second gene of the melibiose operon) of W3133-2 was exactly the same as that of W3133. Activity of alpha-galactosidase (product of the first gene, melA, of the melibiose operon) of W3133 cells grown at 40 degreesC was very low, although that of W3133-2 cells grown at 40 degreesC was high. These observations suggested that expression of the melibiose operon in W3133 is also temperature-sensitive. In fact, we found that the expression in W3133 cells was temperature-sensitive, while that in W3133-2 cells was temperature-resistant, by analyzing mRNA levels using the Northern blot method. Furthermore, we identified mutations in the promoter region of the melibiose operon of W3133-2 that resulted in the elongation of an 18 nucleotide inverted repeat sequence to a 28-nucleotide repeat sequence present immediately upstream of the -35 region. This may stabilize a possible stem structure due to the inverted repeat at 37-42 degreesC.     

Effect of the no-flow interval and hypothermia on cerebral blood flow and metabolism during cardiopulmonary resuscitation in dogs

BACKGROUND and PURPOSE: We sought (1) to determine the effect of brief periods of no flow on the subsequent forebrain blood flow during cardiopulmonary resuscitation (CPR) and (2) to test the hypothesis that hypothermia prevents the impact of the no-flow duration on cerebral blood flow (CBF) during CPR. METHODS: No-flow intervals of 1.5, 3, and 6 minutes before CPR at brain temperatures of 28 degreesC and 38 degreesC were compared in 6 groups of anesthetized dogs. Microsphere-determined CBF and metabolism were measured before and during vest CPR adjusted to maintain cerebral perfusion pressure at 25 mm Hg. RESULTS: Increasing the no-flow interval from 1.5 to 6 minutes at 38 degreesC decreased the CBF (18. 6+/-3.6 to 6.1+/-1.7 mL/100 g per minute) and the cerebral metabolic rate (2.1+/-0.3 to 0.7+/-0.2 mL/100 g per minute) during CPR. Cooling to 28 degreesC before and during the arrest eliminated the detrimental effects of increasing the no-flow interval on CBF (16. 8+/-1.0 to 14.8+/-1.9 mL/100 g per minute) and cerebral metabolic rate (1.1+/-0.1 to 1.3+/-0.1 mL/100 g per minute). Unlike the forebrain, 6 minutes of preceding cardiac arrest did not affect brain stem blood flow during CPR. CONCLUSIONS: Increasing the no-flow interval to 6 minutes in normothermic animals decreases the supratentorial blood flow and cerebral metabolic rate during CPR at a cerebral perfusion pressure of 25 mm Hg. Cooling to 28 degreesC eliminates the detrimental impact of the 6-minute no-flow interval on the reflow produced during CPR. The brain-protective effects of hypothermia include improving reflow during CPR after cardiac arrest. The effect of hypothermia and the impact of short durations of no flow on reperfusion indicate that increasing viscosity and reflex vasoconstriction are unlikely causes of the "no-reflow" phenomenon.     

Reaction of neuronal nitric-oxide synthase with oxygen at low temperature. Evidence for reductive activation of the oxy-ferrous complex by tetrahydrobiopterin

The reaction of reduced NO synthase (NOS) with molecular oxygen was studied at -30 degreesC. In the absence of substrate, the complex formed between ferrous NOS and O2 was sufficiently long lived for a precise spectroscopic characterization. This complex displayed similar spectral characteristics as the oxyferrous complex of cytochrome P450 (lambda max = 416.5 nm). It then decomposed to the ferric state. The oxidation of the flavin components was much slower and could be observed only at temperatures higher than -20 degreesC. In the presence of substrate (L-arginine), another, 12-nm blue-shifted, intermediate spectrum was formed. The breakdown of the latter species resulted in the production of Nomega-hydroxy-L-arginine in a stoichiometry of maximally 52% per NOS heme. This product formation took place also in the absence of the reductase domain of NOS. Both formation of the blue-shifted intermediate and of Nomega-hydroxy-L-arginine required the presence of tetrahydrobiopterin (BH4). We propose that the blue-shifted intermediate is the result of reductive activation of the oxygenated complex, and the electron is provided by BH4. These observations suggest that the reduction of the oxyferroheme complex may be the main function of BH4 in NOS catalysis.     

Metabolic changes during exercise testing of patients with ischaemic heart disease

The applicability of a complement consumption assay as a means by which to detect IgG aggregates and immune complexes in serum was examined. Both heavy (greater than or equal to 19S) and intermediate (11-17S) IgG aggregates were detected and the sensitivity of the assay was greater than or equal to 10 mug aggregated IgG/ml. BSA anti-BSA complexes, formed in slight antibody excess, were detected at a BSA concentration of 200 ng/ml. NHS stored at 4degreesC for greater than or equal to 2-3 weeks or at -20degreesC for more than 3 months developed distinct anticomplementarity (AC). This background AC, due to IgG aggregate formation, was reduced by heating the serum at 56degreesC for 50 min prior to testing. A similar reduction of AC and C1q fixation was observed when IgG aggregated at 61degreesC or 63degreesC was heated further at 56degreesC for 50 min. The abatement of AC could not be correlated to a change in IgG aggregation size. In contrast, AC of preformed antigen-antibody complexes was not reduced by this heat treatment.     

Left ventricular dysfunction following rewarming from experimental hypothermia

This study was aimed at elucidating whether ventricular hypothermia-induced dysfunction persisting after rewarming the unsupported in situ dog heart could be characterized as a systolic, diastolic, or combined disturbance. Core temperature of 8 mongrel dogs was gradually lowered to 25 degreesC and returned to 37 degreesC over a period of 328 min. Systolic function was described by maximum rate of increase in left ventricular (LV) pressure (dP/dtmax), relative segment shortening (SS%), stroke volume (SV), and the load-independent contractility index, preload recruitable stroke work (PRSW). Diastolic function was described by the isovolumic relaxation constant (tau) and the LV wall stiffness constant (Kp). Compared with prehypothermic control, a significant decrease in LV functional variables was measured at 25 degreesC: dP/dtmax 2,180 +/- 158 vs. 760 +/- 78 mmHg/s, SS% 20.1 +/- 1.2 vs. 13.3 +/- 1.0%, SV 11.7 +/- 0.7 vs. 8.5 +/- 0.7 ml, PRSW 90.5 +/- 7.7 vs. 29.1 +/- 5.9 J/m. 10(-2), Kp 0.78 +/- 0.10 vs. 0.28 +/- 0.03 mm-1, and tau 78.5 +/- 3.7 vs. 25.8 +/- 1.6 ms. After rewarming, the significant depression of LV systolic variables observed at 25 degreesC persisted: dP/dtmax 1,241 +/- 108 mmHg/s, SS% 10.2 +/- 0.8 J, SV 7.3 +/- 0.4 ml, and PRSW 52.1 +/- 3.6 m. 10(-2), whereas the diastolic values of Kp and tau returned to control. Thus hypothermia induced a significant depression of both systolic and diastolic LV variables. After rewarming, diastolic LV function was restored, in contrast to the persistently depressed LV systolic function. These observations indicate that cooling induces more long-lasting effects on the excitation-contraction coupling and the actin-myosin interaction than on sarcoplasmic reticulum Ca2+ trapping dysfunction or interstitial fluid content, making posthypothermic LV dysfunction a systolic perturbation.