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Biomedical subjects

M D White

Publications and source records attributed to M D White.

At least 55 records · Page 3Linked to original sources
PubMed1993

Comparison of core threshold temperatures for forehead sweating based on esophageal and rectal temperatures.

A protocol incorporating successive hot and cold water immersions, causing respective warming and cooling of the body, has been used to determine the core threshold for sweating. Disparate results have been reported for the core threshold of sweating, and these have been attributed to the possible existence of core temperature gradients during such a protocol. Spatial and temporal core temperature (Tc, degree C) gradients during dynamic changes in body temperature may give rise to different values of core temperature thresholds for sweating, depending on the Tc measurement site. In addition, during such an immersion protocol skin temperature transients may influence expression of thresholds using esophageal temperature (Tes). With these considerations, the effects of Tc gradients and skin temperature on Tc thresholds for sweating were examined. Subjects (n = 22) were immersed to the neck in 40 degrees C water until Tes reached 38.5 degrees C (phase 1), followed immediately by cooling in 30.6 degrees C water until extinction of sweating was observed (phase 2). Cooling was continued in the latter bath after the sweating extinction until total immersed time reached 50 min or until shivering was initiated (phase 3). During the trials continuous assessment was made of rectal temperature (Tre) and Tes, mean unweighted skin temperature (Tsk, degree C), forehead sweating rate (Esw, g.m-2.min-1), oxygen consumption (VO2, L.min-1), and surface heat flux (Q, W.m-2). With the current protocol it appeared inappropriate to determine the Tc thresholds for onset of sweating, as sweating was initiated prior to any significant displacement of Tc, but was most likely influenced by Tsk and its rate of change.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Arthroscopic lavage and debridement for osteoarthritis of the knee.

We measured the effect of arthroscopic lavage and debridement of the osteoarthritic knee by comparing objective measurements of thigh muscle function before and after operation. There was some improvement in quadriceps isokinetic torque at six and 12 weeks after joint lavage but not after debridement. Neither method significantly relieved the patients' symptoms.

Adult↗
PubMed1992

Relationship between physique and rectal temperature cooling rate.

Despite many attempts to relate components of physique to core temperature cooling rate, no consistent relationship has emerged. The inconsistencies among the reported findings may arise from unaccounted thermoregulatory responses or incomplete physique assessment or both. A study was designed to examine this relationship in the range of rectal temperatures (Tre) within which shivering and sweating are absent, defined as the null zone, thus minimizing the contribution of these effector responses. Twenty healthy subjects (10 male and 10 female), representing a variety of physiques, participated in the study. The anthropometric protocol included 5 heights, body mass, 8 skinfolds, 10 girths, and 4 breadths. This permitted derivation of a body surface-area-to-mass ratio and estimates of adipose and muscle tissue masses using a cadaver-validated mass fractionation model. Subjects were heated in a 40 degrees C bath followed immediately by cooling in a 30.6 degrees C bath. During the cooling, forehead sweating rate and oxygen uptake were monitored to establish the boundaries of the Tre null zone. In addition, on-line recordings were made of Tre, skin temperature, and surface heat flux at six sites. The rate of cooling of Tre (Tre), in the range of temperatures between thresholds for sweating and shivering, was correlated to the components of physique. Estimates of adipose and skeletal muscle tissue masses did not correlate to Tre in the range of core temperatures investigated. However, total mass exhibited a significant correlation (r = 0.5, P less than or equal to 0.05) with Tre, but gender seemed to distort this relationship, possibly due to differences in adipose tissue distribution.

Adipose Tissue↗
PubMed1990

Monitoring of transplant patients' lymphocytes: knowledge of the varying specificities of anti-lymphocyte antibodies allows the interpretation of anomalous results.

In many transplant centers, the T lymphocytes of transplant patients are routinely monitored, both to predict and diagnose the cellular events that result from transplantation and to evaluate the effectiveness of immunosuppressive therapy. During the course of this monitoring, we have observed anomalous results: the number of T cells said to be present varies greatly depending on the surface marker used for the assay. It is shown, in this study, that these "anomalous" results can be predicted from a knowledge of the spectrum of specificity of the anti-lymphocyte antibody therapy being administered. Because polyclonal antibodies have varied and unstated specificities, it is difficult to interpret results obtained from monitoring T-cell numbers or subset ratios without some knowledge of the specificities of the drugs being used.

Antibodies↗
PubMed1990

Blood transfusion and surgery: the effect on growth of a syngeneic sarcoma.

The effects of blood transfusion, blood components, and surgical trauma on the growth of an experimental sarcoma have been examined. Recipient animals were inbred adult female WAB rats, which received allogeneic transfusions from inbred adult female PVG rats, syngeneic blood from inbred colony-mates, or saline infusions. Small volume transfusions (1-4 ml) of whole blood had no effect on tumour growth, but growth of the MC7 sarcoma was significantly enhanced following allogeneic transfusions of 5 ml whole blood, or when 4 ml was combined with sham laparotomy. Maximal enhancement of tumour growth occurred when 4 ml transfusions of allogeneic washed cells were given, but allogeneic plasma was also able, to a lesser degree, to enhance tumour growth. These data confirm that blood transfusion may enhance growth of the MC7 sarcoma, that the effect may be dose dependent, and synergistic with the immunosuppression of surgery. Many components of an allogeneic transfusion may be responsible for this effect.

Animals↗
PubMed1989

Characterization of the terminal cisternae and longitudinal tubules of sarcoplasmic reticulum from malignant hyperpyrexia susceptible porcine skeletal muscle.

1. The sarcoplasmic reticulum (SR) from malignant hyperpyrexia susceptible (MHS) and control porcine skeletal muscle was separated into vesicular fractions enriched in the membrane elements of the terminal cisternae and longitudinal tubules. 2. The two membrane preparations were highly purified and had distinctive features which were associated with their origins in the SR membraneous network. 3. Calsequestrin and calcium were enriched in the terminal cisternae fraction (HSR), in comparison to longitudinal tubule preparations (LSR). 4. The HSR membrane also had a greater total capacity to store Ca2+ and Ca2+ release was more rapid than from LSR preparations. 5. No distinction could be made between the membrane morphology, Ca2+ -fluxes or Ca2+ -dependent ATPase activities, associated with these functionally distinct regions of MHS and control preparations.

Animals↗
PubMed1988

Calmodulin-antagonist drugs and porcine malignant hyperpyrexia.

1. Landrace swine were identified as malignant hyperpyrexia susceptible (MHS) or control by the contracture responses of gracilis muscle fibre bundles to 3% halothane, 2 mmol/l caffeine and 80 mmol/l KCl. The effects of calmodulin-antagonist drugs on the contractile behaviour of control and MHS preparations were investigated in vitro. 2. Calmodulin-antagonists at micromolar concentrations induced contracture in both control and MHS muscle. Pretreatment of MHS muscle with calmodulin-antagonist drugs potentiated its response to halothane and caffeine. 3. These results suggest that calmodulin-antagonist drugs cause an increase in myoplasmic Ca2+ concentration in both control and MHS muscle.

Animals↗
PubMed1988

Disintegration of microorganisms.

The most common methods for the large-scale disintegration of microorganisms are high-pressure homogenization and wet milling. The most-used homogenizer is produced by Manton Gaulin and the common ball mill is the Dyno-Mill. Other manufacturers are now producing similar equipment (e.g., Rannie homogenizers and Netzsch ball mills). However, only relatively limited information on these systems has been published so far. An additional system that might become available for large-scale disintegration is microfluidization. When coming to choose optimal equipment and conditions for cell disintegration, it might be useful to consider some relevant topics that were compiled by the Retsch company for particle disruption and are presented, with modification, in Table XIII. Obviously, the importance of the above points will vary in different processes, but all of them should be considered in any biotechnological large-scale application. It is important to realize that although the mechanical disintegration methods are of general use, it is essential to define the optimal disintegration conditions for each microorganism and/or product. As a starting point, the published data for a similar product should be consulted. This should be followed by laboratory-scale experiments carried out with equipment and conditions that can be easily scaled up.

Cell Fractionation↗
PubMed1987

Thiophosphorylation of skeletal muscle sarcoplasmic reticulum in porcine malignant hyperpyrexia.

1. The basal, Ca2+-dependent and Mg2+-dependent thiophosphorylation of malignant hyperpyrexia-susceptible (MHS) porcine skeletal muscle was investigated. 2. Seven major proteins of Mr 100,000-11,000 were substrates for thiophosphorylation. 3. Sodium molybdate significantly elevated all levels of thiophosphorylation in control sarcoplasmic reticulum, but did not effect the Ca2+-dependent thiophosphorylation of MHS samples. 4. These results suggest that MHS sarcoplasmic reticulum may have altered sensitivity to protein phosphatase inhibition.

Adenosine Triphosphate↗
PubMed1987

Calmodulin in porcine malignant hyperpyrexia.

The anaesthetic complication malignant hyperpyrexia (MH) is due to an elevation of the myoplasmic Ca2+ concentration. Examination of calmodulin isolated from MH susceptible swine suggests that the disorder in calcium regulation in MH is not due to an abnormality in calmodulin.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1987

The effects of calmodulin antagonist drugs on isolated sarcoplasmic reticulum from malignant hyperpyrexia susceptible swine.

1. Because calcium antagonist drugs increase contracture in both control and malignant hyperpyrexia susceptible (MHS) skeletal muscle, the effect of these drugs on the sarcoplasmic reticulum (SR) was investigated. 2. The calmodulin antagonist drugs inhibited the Ca2+ dependent ATPase activity and the ATP-dependent Ca2+ uptake, and accelerated the efflux of Ca2+ from isolated SR preparations from both control and MHS skeletal muscle. These effects of calmodulin antagonist drugs on SR Ca2+ transport functions were consistent with their in vitro pharmacological effects on control and MHS muscle.

Adenosine Triphosphate↗
PubMed1987

Effects of adenylate cyclase activators on porcine skeletal muscle in malignant hyperpyrexia.

The effect of adenylate cyclase activation on the in vitro contractures of control and malignant hyperpyrexia susceptible (MHS) porcine muscle was investigated. While fluoride and molybdate ions potentiated drug-induced contractures in control muscle, other activators of adenylate cyclase (forskolin and noradrenaline) did not. Furthermore, fluoride and molybdate had no effect on MHS skeletal muscle contractility. Cyclic AMP content, basal adenylate cyclase activity and molybdate-stimulated adenylate cyclase activity of MHS skeletal muscle was not significantly different from that of control muscle. It is concluded that increased activity of adenylate cyclase does not represent the primary skeletal muscle defect which predisposes to porcine MH.

Adenylyl Cyclases↗
PubMed1987

The effect of oxytocin on porcine malignant hyperpyrexia susceptible skeletal muscle.

1. Certain commercial preparations of oxytocin have been reported to reverse the development of pale soft exudative meat and malignant hyperpyrexia (MH) in pigs in vitro. 2. In this study it is shown that preservative-free oxytocin has no significant effect on the characteristic contractures of MH susceptible (MHS) muscle to halothane, caffeine, succinylcholine and KCl in vitro. 3. Whilst a commercial preparation of oxytocin, Syntocinon (containing chlorbutol as preservative), reversed and prevented the MHS characteristic responses, this study demonstrates conclusively that this was entirely due to the preservative chlorbutol.

Animals↗
PubMed1987

Direct toxic effect of the radiocontrast agent diatrizoate on renal proximal tubule cells.

The pathophysiology of radiocontrast agent-induced acute renal failure is presently unclear. To test for a possible direct deleterious effect of diatrizoate, a commonly used radiocontrast agent, on renal tubule cells, suspensions enriched in rabbit proximal tubule segments were incubated with sodium diatrizoate. After these manipulations, a variety of well-established metabolic parameters to quantitate the extent of cell injury were measured. Diatrizoate sodium (25 mM) produced significant declines in tubule K+, ATP, and total adenine nucleotide (TAN) contents, significant decreases in tubule basal and uncoupled respiratory rates, and a significant increase in tubule Ca2+ content, demonstrating the development of cell injury induced by diatrizoate. These effects were dose related and were progressive with increasing incubation time from 97.5 to 157.5 min. The effects of N-methylglucosamine (meglumine) on renal tubule cell viability was also evaluated. Meglumine is a low molecular weight amino-substituted cationic compound and is commonly added to radiocontrast dye solutions. Meglumine (25 mM) had significant effects to lower tubule K+ content and to decrease both tubule basal and uncoupled respiratory rates. These alterations were slightly additive to diatrizoate in that meglumine diatrizoate produced greater alterations in tubule-metabolic parameters compared to diatrizoate sodium. A period of 22.5 min of hypoxia also caused deleterious changes in each of these quantitative indices of cell viability, and diatrizoate potentiated the degree of hypoxia-induced cell injury. These results demonstrate that the radiocontrast agent, diatrizoate, is directly toxic to renal proximal tubule cells. Meglumine, a cation added to diatrizoate containing radiocontrast solutions, also had a moderate toxic effect on renal epithelial cells and added to the toxicity of diatrizoate. Diatrizoate also aggravated the degree of cell injury induced by a 22.5-min period of hypoxia. These experiments thus provide evidence for a direct toxic effect of diatrizoate on proximal renal tubule cells which was additive to hypoxic cell injury.

Animals↗