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Biomedical subjects

L Stevens

Publications and source records attributed to L Stevens.

At least 19 recordsLinked to original sources
PubMed1995

Structure-function relationship of soleus muscle fibres from the rhesus monkey.

Functional and structural properties of rhesus monkey skinned fibres were studied in order to examine the relationship between calcium/strontium (Ca/Sr) activation characteristics and protein composition. The fibres were classified according to their Ca/Sr affinity into slow (61%) and fast groups (39%). According to the myosin isoform composition, two additional hybrid types were defined. Thus, four profiles were characterized: two corresponding to slow (S) and fast (F) isoforms and two corresponding to a mixed proportion of slow and fast isoforms. They were called hybrid slow (HS) or hybrid fast (HF) based on the predominant myosin isoform. Tension/pCa parameters and maximal shortening velocities were determined. S fibres showed a higher pCa threshold and affinity as well as shallower slopes of their tension/pCa curve than did F fibres. HS and HF fibres exhibited tension/pCa curves which were positioned close to those of S and F fibres, respectively. No significant difference was observed between S and HS fibres or between F and HF fibres. Maximal shortening velocity values were higher for fibres expressing predominantly fast myosin isoforms. We suggest than when both S and F isoforms of myofibrillar proteins are expressed in a muscle fibre, the functional properties are mainly governed by the predominant isoform.

Animals↗
PubMed1992

Unfolding and refolding of hen egg-white riboflavin binding protein.

The unfolding and refolding of riboflavin-binding protein (RfBP) from hen egg-white induced by addition of guanidinium chloride (GdnHCl), and its subsequent removal by dialysis have been studied by c.d. and fluorescence for both the native and reduced protein. The reduction of its nine disulphide bonds causes a reduction in the secondary structure (alpha-helix plus beta-sheet) from 63% to 33% of the amino acid residues. Unfolding of the native protein occurred in two phases; the first involving a substantial loss of tertiary structure, followed by a second phase involving loss of secondary structure at higher GdnHCl concentrations. By contrast this biphasic behaviour was not discernible in the reduced protein. The loss of ability to bind riboflavin occurred after the first phase of unfolding. Comparison of unfolding of the holoprotein and apoprotein suggested that riboflavin has only a small stabilizing effect on the unfolding process. After removal of GdnHCl, the holoprotein, apoprotein and reduced protein assumed their original conformation. The significance of the results in relation to various models for protein folding is discussed.

Animals↗
PubMed1992

Biliary complications in pediatric liver transplantation. A comparison of reduced-size and whole grafts.

One of the major changes in liver transplantation has been the application of reduced-size liver transplants(RLT). RLT has the great advantage of expanding the donor pool up to ten times the weight of the recipient, thereby decreasing pretransplant mortality in the pediatric age group. It has been suggested that RLT is a risk factor for biliary complications. To analyze the role of RLT and biliary complications, the results of 213 consecutive liver transplants in 164 pediatric patients over a 6-year period will were reviewed. These included 113 whole-liver transplants and 100 reduced-size liver transplants (49 reduced cadaveric liver transplants (RCLT), 38 split-liver transplants (SLT) and 13 living-related liver transplants (LRLT). The average weight and age were significantly higher in recipients receiving whole-size grafts (average weight 18.4 mg, average age 4.9 years) than in those receiving reduced size grafts (average age 2.3 years, average weight 11.1 kg). Biliary reconstruction consisted of Roux-en-Y, cholangiojejunostomy (n = 203) or choledochocholedochostomy (n = 10). There were 29 total biliary complications, (13.6%) with no significant difference in the complication rate between the whole (n = 13, 11.5%) or reduced livers (n = 16, 16%). Biliary leakage was the most common complication (n = 20), and it occurred at the biliary enteric anastomoses (n = 10), the roux limb (n = 7), or at the cut edge (n = 3). Of the leaks occurring at the biliary enteric anastomoses, 50% were caused by hepatic artery thrombosis. Biliary obstruction accounted for their remaining complications (n = 9) or 4.2%. Actuarial survival from 6 years to a minimum of two months of follow-up was 73% in the whole-size and 70% in reduced-size liver transplants. This series demonstrates that the incidence of biliary complications is similar in reduced-size and full-size grafts. No grafts were lost to biliary complications in the absence of hepatic artery thrombosis.

Biliary Tract Diseases↗
PubMed1992

Ca2+ movements in sarcoplasmic reticulum of rat soleus fibers after hindlimb suspension.

The functional capacity of skeletal muscle sarcoplasmic reticulum (SR) was examined in the slow soleus of rats submitted to 15 days of disuse produced by hindlimb suspension (HS). By using caffeine-induced contractions of single skinned fibers, Ca2+ uptake, Ca2+ release, and passive Ca2+ leakage through the SR membrane were investigated. In the SR of atrophied muscles, the amounts of Ca2+ uptake and Ca2+ release were significantly higher than in the control muscles and were close to those found for a fast muscle, the plantaris. Moreover, the study of the Ca2+ leakage showed that the time required to empty the SR previously loaded with Ca2+ was reduced by a factor of two after HS. Such disturbances of the Ca2+ movements in the SR suggested that alterations of the SR membrane occurred after HS. The results supported the idea that after hindlimb unweighting the slow soleus muscle acquired SR properties that were very much like those of a faster muscle.

Animals↗
PubMed1992

Outcome of renal transplantation in children aged 1-5 and 6-18 years.

Results of renal transplantation in younger children have not been very encouraging in the past. We therefore studied the effect of newer immunosuppressive regimens on the outcome of renal transplantation of 5 children aged 2.9 +/- 1.3 years (range 1.6-5.0), and compared it to 10 children of an older pediatric patient group aged 11.4 +/- 4.4 years (range 6.0-18.5). All patients with the exception of 1 underwent dialysis. The percentage of cadaveric and live-related transplants was similar in both groups. Recipients of a cadaveric transplant had at least 3 blood transfusions; recipients of live-related transplants had donor-specific transfusions with azathioprine. Posttransplantation immunosuppression consisted of prednisone and azathioprine; recipients of cadaveric transplants received also ciclosporin. Rejection episodes and side effects (hypertension, hirsutism) were comparable in both groups. In the younger patient group, 1 patient died of a congenital lung abnormality but had a functioning graft. In the older patient group, 1 patient lost his graft 16 months posttransplantation due to reduction of his immunosuppressives, necessitated by a severe CMV infection. Growth and development improved in the younger patient group, but was stable in older patients. Renal transplantation is a suitable option in younger pediatric patients. Graft survival rates are comparable to those of older patients.

Adolescent↗
PubMed1991

Egg white proteins.

1. Egg white proteins are the principal solutes present in egg white, making up approximately 10% of its weight. 2. They are globular proteins and most have acidic isoelectric points. 3. Many are glycoproteins with carbohydrate contents ranging from 2 to 58%. 4. Of the major egg white proteins, lysozyme is the only one having catalytic activity, but many have specific binding sites, e.g. for vitamins such as biotin, riboflavin and thiamin, or for metal ions such as FeIII. 5. A major group are those showing proteinase inhibitory activity, and they include ovomucoid, ovoinhibitor, cystatin and ovostatin. 6. The synthesis of egg white protein occurs in the oviduct, and is hormonally controlled either by oestrogens or progesterone. 7. Extensive studies have been carried out in the genes coding for egg white proteins.

Animals↗
PubMed1991

A comparative study of the structure of egg-white riboflavin binding protein from the domestic fowl and Japanese quail.

1. The riboflavin binding proteins from domestic fowl and Japanese quail have been isolated and their structures compared by circular dichroism, fluorescence and peptide mapping. 2. The two proteins have similar secondary structures, but differ in their tertiary structures as reflected in the environments of aromatic amino acid side chains. 3. Differences in amino acid sequence between the proteins are indicated by the digestion patterns obtained with thermolysin, chymotrypsin and V8 proteinase from Staphylococcus aureus. Both proteins are resistant to digestion by trypsin.

Animals↗
PubMed1991

Liver transplantation in children from living related donors. Surgical techniques and results.

Pediatric liver transplantation with reduced size donor organs (RLT) has evolved into a standard clinical procedure increasing the choices of recipients for their treatment. Nevertheless organ availability remains a major problem. The authors therefore have proposed to study the use of hepatic segments from living related donors (LRT) in a group of 20 children less than 2 years of age or weighing less than 15 kg, in whom standard indications for transplantation existed. Volunteer related donors were selected after medical and psychiatric evaluations, and the suitability of the donor's liver was established by functional and radiologic criteria. A two-stage informed consent process assured appropriate "volunteerism." Nineteen infants received LRT as first grafts and one as a second graft. Seventeen of the recipients are alive 3 to 18 months after LRT. Fifteen of 20 patients are currently at home with the original graft and normal liver function (bilirubin less than 1.5 mg/dl) after a median hospital stay of 27 days (range, 14-93 days). Four patients underwent retransplantation, in all cases due to arterial thrombosis. The overall graft survival for 20 primary LRTs is 75%, with follow-up between 3 and 18 months. A number of technical problems occurred during our initial trial, the most aggravating being vascular thrombosis. Refined approaches to vascular reconstruction should reduce the incidence of thrombosis and improve the rate of survival in future cases. The donor group for the initial 20 LRT procedures comprised 12 mothers, 7 fathers, and 1 grandmother. In addition one father and one uncle, who was an identical twin of the recipient's father, who did not qualify for anatomic reasons, were used in repeat LRT. All donors survived and are now in normal health between 3 and 18 months after LRT, having returned to all activities enjoyed before donation. The median hospital stay was 6 days (range, 5-14). Complications were minimal, and all were limited to the first three procedures, in which a full left hepatectomy was performed. After alteration of the procedure into a left lateral segmentectomy, no complications were encountered. The left lateral segmentectomy presents minimal surgical trauma to the liver and should remain the primary approach for obtaining a liver graft from a living donor. For children, transplantation of a left lateral segment from a live donor provides a new way of providing a transplant of appropriate size and with good function. The success of this program has led to the acceptance of LRT for general clinical application in the authors' institution.

Adult↗
PubMed1990

Cytoplasmically inherited reproductive incompatibility in Tribolium flour beetles: the rate of spread and effect on population size.

This paper reports on the effects of a cytoplasmically inherited reproductive incompatibility in different genetic strains of the flour beetle, Tribolium confusum. We measured the rate of spread and the effect of host population size using different initial frequencies of infection with a cytoplasmic factor that mediates reproductive incompatibility. There were two experiments, in one the infected and uninfected lines were from the same genetic strain, b-Yugoslavia. In the other, the infected line was from the "high cannibalism" bIV strain and the uninfected line from the "low cannibalism" bI strain. We estimate that the fitness ratio of infected to uninfected in b-Yugoslavia is 0.63 and the observed rate of spread for this strain corresponds to a model of cytoplasmic inheritance that takes into account the productivity differences between the infected and cured lines. In the bI-bIV experiment, because the uninfected and infected lines are from different genetic strains, we cannot partition the effects of the cytoplasmic factor from other factors. The rate of spread in the bI-bIV experiment is faster in males and slower in females than predicted from a model of cytoplasmic inheritance. In both experiments, productivity varies with initial infection frequency; however, the relationship is not explained by a simple model that predicts lower population size at intermediate infection frequencies.

Animals↗
PubMed1990

An observationally based rating scale for affective symptomatology in child psychiatry.

There is growing dissatisfaction with current methods for rating affective symptoms in children. We report findings from a preliminary psychometric study of an alternative approach, that of direct observational ratings. The Emotional Disorders Rating Scale (EDRS) is an observation-based instrument containing 59 items divided into eight subscales. The results of this study indicate that measurement of nonverbal components of affective symptoms in children is feasible. Interrater reliability and internal consistency of the EDRS subscales were high. The EDRS also has potential as a measurement of state-related changes in affective behavior and as a technique for examining treatment response.

Adolescent↗
PubMed1990

Rupture of the distal thoracic esophagus following blunt trauma: case report.

Rupture of the distal thoracic esophagus is an unusual injury following blunt abdominal trauma. We recently encountered this injury in a patient following a relatively minor motor vehicle accident. An improperly positioned seatbelt was presumed contributory in this case. Prevention of further contamination and drainage of infection are primary objectives. Wide mediastinal drainage with repair, resection, or diversion are recommended, depending on the degree of mediastinitis present.

Accidents, Traffic↗
PubMed1990

The use of electrically stimulated skeletal muscle to pump blood.

Electrically stimulated skeletal muscle can be used in many ways to pump blood. The important physiological characteristics of skeletal muscle for use in a cardiac assist role are presented. The force developed by a twitch and tetanic contraction are quantitated and the considerations in the choice of the stimulus applied to the innervating motor nerve are discussed. The importance of stimulus frequency and duration of the stimulus train are presented in terms of the stroke volume produced by skeletal muscle contracting around a pouch. The effect that preload has on pouch stroke volume and muscle blood flow are demonstrated. Finally an example is given in which cardiac output is augmented by an untrained, electrically stimulated, canine rectus abdominis muscle wrapped around a pouch connected between the apex of the left ventricle and the aorta. In this study, the augmentation in cardiac output was measured when the skeletal muscle was contracted after each second, third, and fourth ventricular contraction. The augmentation was 46% +/- 4, 31% +/- 7, and 25% +/- 4, respectively, for the three contraction regimens. Although electrically stimulated skeletal muscle can be used as a power source to assist the failing heart, the optimum application is yet to be discovered. Important considerations in selecting the optimal application are preload, stimulus train duration, train rate, and muscle blood flow.

Abdominal Muscles↗
PubMed1990

Dimensional change of impressions on sterilization.

The volume of impressions, before and after disinfection in a gluteraldehyde solution for longer than ten hours (that is, sterilization), was measured indirectly from dies produced from the impressions. Three elastomeric impression materials were used in both acrylic resin and poly-vinyl-chloride 'trays' to form the impressions. One impression material appeared to be practically superior to the others with respect to variability of volume. The effect of tray material on change in volume (calculated as after disinfection minus before disinfection) was significant for one impression material; acrylic trays produced the greatest effect. The change in volume was significant for two impression materials; acrylic trays were associated with greater increase in volume. It was concluded that if impressions are to be sterilized, a tray material having minimal potential to absorb disinfectant should be used.

Dental Impression Materials↗
PubMed1990

Contractile properties of rat soleus muscle after 15 days of hindlimb suspension.

The properties of the contractile elements interacting to develop force in atrophied rat soleus muscle were studied by using single skinned fibers, which permitted direct access to the contractile apparatus. Muscle atrophy was induced by 15 days of hindlimb suspension. Suspension resulted in a decrease of maximal tension relative to an important decline in fiber diameter. Ca affinity of the contractile proteins was not changed insofar as the tension-pCa relationship was not shifted along the pCa axis. However, after hindlimb suspension 1) the value of the Hill coefficient from the tension-pCa curve was found to be higher, 2) a higher Ca threshold for activation was reported, and 3) a significant increase in contraction kinetics was described. All these results suggested that after suspension the mechanical properties of the slow-twitch soleus appeared to resemble more closely those of a fast-twitch muscle. Our results were in complete agreement with published histochemical data.

Animals↗