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Biomedical subjects

B L Baker

Publications and source records attributed to B L Baker.

At least 37 records · Page 2Linked to original sources
PubMed1994

Quantification of the interaction between lysolecithin and phospholipase A2.

The rate of hydrolysis of phosphatidylcholine bilayers by phospholipase A2 may be either enhanced or inhibited by the presence of lysolecithin depending on the experimental conditions examined. To further understand the relationship of lysolecithin to phospholipase A2 activity, the binding of lysolecithin to phospholipase A2 from the venom of Agkistrodon piscivorus piscivorus was examined by fluorescence spectroscopy. The tryptophan emission intensity of the enzyme was enhanced by 70% upon addition of lysolecithin. The binding isotherm for lysolecithin to the phospholipase A2 estimated from the fluorescence change was biphasic, with a clear break in the curve occurring at the critical micelle concentration of the lysolecithin. Several observations suggested that the phospholipase A2 was capable of hydrolyzing the lysolecithin although at a rate far below that of phospholipid hydrolysis. These experiments were repeated using several other species of phospholipase A2, and the results were found to be general among the enzymes except the lys-49 isozyme from A. p. piscivorus which displayed neither the dependence on the critical micelle concentration for binding nor the ability to hydrolyze lysolecithin. These results were used as the basis for a quantitative analysis of enzyme fluorescence changes that occur during the time course of phospholipid hydrolysis and of the mechanism whereby lysolecithin inhibits the hydrolysis of phosphatidylcholine bilayers by phospholipase A2.

Agkistrodon↗
PubMed1994

The development of a mutation in the precore region of the hepatitis B virus in a chronically infected individual.

Over a 15-year period, a white American woman was observed to have progressive hepatitis B that underwent hepatitis Be antigen (HBeAg) positivity to anti-HBe positivity with development of cirrhosis. This patient was found to have a non-sense mutation in the second codon of the pre-C region of the hepatitis B virus genome after her anti-HBe seroconversion but not in her serum when she was HBeAg+. As controls, serial blood specimens were analyzed from 12 other American patients who spontaneously converted from HBeAg to anti-HBe, who underwent an interferon alfa-associated HBeAg to anti-HBe seroconversion, and who did not seroconvert with interferon alfa therapy. No mutations in the pre-C region were observed to arise in these individuals. In conclusion, non-sense mutations that occur in the pre-C region in locations other than the 28th codon can be associated with HBeAg negative progressive liver disease. This report of a non-sense mutation occurring over time is unusual in that it occurred in a white American patient.

Adult↗
PubMed1994

Family involvement in residential treatment of children with retardation: is there evidence of detachment?

Family involvement could be critical for successful residential treatment. Historically, however, out of home placement for children with mental retardation meant a severing of meaningful ties with their families. Today, families have greater involvement with pre-placement services and might be more involved in residential treatment as well. Families (N = 55) were interviewed twice, approximately one and two years after placement, to assess their involvement with the child and their reactions to placement. Contrary to previous findings, family involvement was high and stable; there was no evidence of behavioral detachment. Moreover, respondents primarily reported post-placement benefits to the family. Family emotional reactions were considered within a framework of "psychological tasks of placement".

Child↗
PubMed1994

Increased alveolar/capillary membrane resistance to gas transfer in patients with chronic heart failure.

OBJECTIVE: To investigate pulmonary diffusive resistance to gas exchange in patients with heart failure and healthy volunteers, assessing the relative contributions of the alveolar/capillary membrane and pulmonary capillary blood. SETTING: Hospital outpatient department and pulmonary function laboratory. PATIENTS: 38 patients (mean age 60) receiving treatment with loop diuretics and angiotensin converting enzyme inhibitors for stable symptomatic heart failure of > 6 months duration (New York Heart Association (NYHA) classes II and III). Results were compared with those of 17 healthy volunteers (mean age 52). METHODS: The alveolar/capillary membrane diffusive resistance and the pulmonary capillary blood volume available for physiological gas exchange were determined by the Roughton and Forster method, which measures the single breath pulmonary diffusing capacity for carbon monoxide at varying alveolar oxygen concentrations. RESULTS: Total pulmonary diffusive resistance was higher in patients than controls. Alveolar/capillary membrane resistance formed the main component of this increase, accounting for a mean (SD) of 63% (20%) and 86% (8%) of total pulmonary diffusive resistance in patients in NYHA II and III classes respectively, compared with 53% (10%) in controls. The pulmonary capillary blood volume was not significantly different between controls and patients in NYHA class II (66 (18) ml v 61 (18) ml), but was increased in those in NYHA class III (95(46) ml, P < 0.05). CONCLUSION: This study confirmed impairment of pulmonary diffusion at rest in patients with chronic heart failure and identified impaired alveolar/capillary membrane function as the main factor responsible.

Adult↗
PubMed1993

Quantification of the interaction of lysolecithin with phosphatidylcholine vesicles using bovine serum albumin: relevance to the activation of phospholipase A2.

The activity of soluble phospholipase A2 to hydrolyze phosphatidylcholine vesicles increases abruptly after a lag time of several minutes. The onset of this apparent activation event probably results from the accumulation of a threshold mole fraction of the hydrolysis products (lysolecithin and fatty acid) in the bilayer. One important observation relevant to the mechanism of this activation process is the biphasic dependence of the lag time on vesicle concentration. To test whether this dependence can be attributed entirely to the strength of partitioning of the lysolecithin into the phosphatidylcholine bilayer, we estimated the apparent partition coefficient of lysophospholipid in the membrane of phosphatidylcholine vesicles. Based on competition between bovine serum albumin and the vesicles for the lysophospholipid, we estimated the partition coefficient to be about 5.10(-7) for palmitoyl lipids at 39 degrees C and about 9.10(-7) for myristoyl lipids at 22 degrees C. These values were able to rationalize the behavior of the lag time with dipalmitoylphosphatidylcholine vesicles, but they were unable to predict the behavior with dimyristoylphosphatidylcholine. Therefore, it appears that the complete dependence of the lag phase on vesicle concentration must be explained by additional means such as the possible contribution of nascent fatty acid or previously proposed kinetic activation mechanisms.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1993

The impact of young children with externalizing behaviors on their families.

Compared the impact on families of young children with externalizing behaviors (e.g., hyperactive, aggressive; n = 22), autism (n = 20), or no significant problem behaviors (n = 22) on several measures of family functioning. Previous studies have found heightened stress and parental maladjustment in families with externalizing children. The present study expanded upon that literature by (1) including a clinical control group to determine the specific impact of externalizing problems, (2) focusing on preschool aged children, and (3) using a new measure to directly ascertain parents' perception of impact. Compared to parents with normally developing children, parents with externalizing children reported more negative impact on social life, more negative and less positive feelings about parenting, and higher child-related stress. Moreover, parents of externalizing children reported levels of impact and stress as high as those reported by parents of children with autism. On broader measures of parental and marital well-being, however, the three groups of families of preschoolers did not differ. The implications of these findings for intervention are discussed.

Aggression↗
PubMed1993

Family involvement in residential treatment of children with psychiatric disorder and mental retardation.

OBJECTIVE: The goals of the study were to determine the extent of family involvement with children in residential treatment settings, to examine whether involvement diminishes over time, and to examine the relationship between involvement and the child's diagnosis as well as the demographic characteristics of the child and the family. METHODS: Staff rated the level and frequency of family involvement with 234 children, aged five to 19 years, living in three residential treatment centers. The children were grouped according to three diagnostic categories: psychiatric disorder, mental retardation, and dual diagnosis of psychiatric disorder and mental retardation. RESULTS: Almost one-third of the children had no family contact, and about 50 percent had three or fewer contacts per year. The level of family involvement was lower with dually diagnosed children than with children who had only psychiatric disorder or mental retardation. Level of involvement was also related to the driving time between the family home and the residential facility and to socioeconomic status, variables that seemed to account for the lower level of involvement of families with dually diagnosed children. CONCLUSIONS: Greater distance between the family home and the residential treatment center and low socioeconomic status greatly limit a family's accessibility for involvement with children in out-of-home placements. These obstacles are more likely to occur in families of dually diagnosed children.

Adolescent↗
PubMed1993

Out-of-home placement for children with mental retardation: dimensions of family involvement.

The involvement of families with a child who has mental retardation in residential placement was studied. Sixty-two families who had placed their child out of the home within the previous 2 years were interviewed about behavioral and emotional aspects of involvement. Involvement was high, with 81% of families having at least a monthly visit with their child. There was only marginal evidence for detachment, a lessening of involvement over these 2 years. Although family involvement related to several child and family characteristics, the strongest relation was with facility characteristics, especially opportunities for involvement in the facility.

Adolescent↗
PubMed1992

Reversibility of the activation of soluble phospholipase A2 on lipid bilayers: implications for the activation mechanism.

The time-courses of hydrolysis of large vesicles of dipalmitoylphosphatidylcholine were compared using four species of phospholipase A2 (Agkistrodon piscivorus piscivorus, Crotalus adamanteus and Naja naja venoms and porcine pancreatic). In all four cases, the hydrolysis rate suddenly increases 10 to 100-fold at the time (tau) when a specific mole fraction of reaction products has accumulated. The intrinsic fluorescence emission of the three venom enzymes also increases suddenly at time tau. Both the activation and the fluorescence change are reversible with a half-time of about 50 s for the activity and 2 to 6 s for the fluorescence. These reversal rates and the vesicle concentration dependence of tau are considered for monomer and dimer enzyme activation models. Apparently, at least three states of the enzyme exist beyond the initial unbound state: (1) inactive and bound, (2) inactive with high fluorescence and (3) active. The dimer model already contains the necessary number of states but requires that the activation rate be much lower than the reversal rate to account for the vesicle concentration dependence of tau. Success of the monomer model requires an enzyme state additional to those proposed previously. Although these results do not exclude either the monomer or dimer models conclusively, they do impose important constraints on each model.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1992

A controlled trial of naloxone infusions for the pruritus of chronic cholestasis.

To test the hypothesis that opioid agonist activity contributes to the pruritus of cholestasis, a placebo-controlled single-blinded trial of naloxone, an opioid antagonist, was conducted in eight patients with primary biliary cirrhosis. After discontinuation of all conventional antipruritic medications, one or two continuous (24-hour) IV infusions of naloxone (0.2 micrograms.kg-1.min-1) and placebo solution were administered consecutively in an order that was not predetermined. Pruritus was assessed subjectively by means of four hourly recordings of a visual analogue score. In addition, objective measurements of scratching activity that were independent of gross body movements were continuously recorded using an apparatus specifically designed to measure the frequencies associated with this activity. No side effects associated with naloxone infusions were observed. Only scratching activity data obtained for the same periods of day and night during both naloxone and placebo infusions were compared. Naloxone infusions were consistently associated with a decrease in values of the scratching activity index. In addition, in 50% of the patients the infusions were associated with a decrease in visual analogue score. The mean decrease in scratching activity ranged from 29% to 96% (mean, 50%; P less than 0.001). These findings imply that increased opioid agonist activity contributes to scratching activity in cholestatic patients.

Adult↗
PubMed1992

Social skills and their correlates: preschoolers with developmental delays.

Fifteen preschool-age children with mild mental retardation (developmental delays) from mainstreamed schools were observed during two structured play sessions with matched peers without mental retardation. Children with developmental delays spent more time alone and when they played, showed less social play. The two groups did not differ on communication behaviors that maintained play or in negative affect; however, the children with developmental delays evidenced more disruptive entry, more regressive behaviors, and less positive affect. Families were interviewed concerning their attitudes about, and teaching of, social skills. For the children without mental retardation, level of social play was positively related to the family's teaching and the child's communication abilities. For the children with delays, social play related to developmental age and communication ability but not to family teaching.

Child, Preschool↗
PubMed1992

Toward meaningful family involvement in out-of-home placement settings.

In this paper we have attempted to heighten awareness that meaningful family involvement must be part of program planning for community residential services. The family can be a powerful resource for social support, guidance, and advocacy for individuals with mental retardation living out of the natural home. The dilemma is that investigators have found disappointingly low levels of family involvement. A prospective look at family involvement in the post P.L. 94-142 era, however, suggests that parents who are highly involved with services for their child preplacement may be primed for considerable involvement postplacement. We argued that personnel in placement settings, in part because of carprovider ambivalence toward parents, may not be ready for more family involvement. Recommendations for policy makers and service providers to enhance family involvement were made.

Adult↗
PubMed1991

Effects of parent training on families of children with mental retardation: increased burden or generalized benefit?

Parents of children with mental retardation have become increasingly involved in special education, including training programs to facilitate teaching at home. Although some writers have argued that families accrue generalized psychological benefits of such participation, others have cautioned that the result may be increasing the burden of child-rearing. Forty-nine families of children with mental retardation were assessed before and after a parent training program, on a variety of parent, marital, and family measures. Parents reported high satisfaction with the program and showed small but statistically significant decreases in reports of symptoms of depression, parent and family problems, overall family stress, and dissatisfaction with the family's adaptability. Family characteristics were also predictive of teaching at home one year following training. The families that reported doing the least productive teaching had entered training reporting greater child-related stress and lower satisfaction with the marriage and the family.

Adaptation, Psychological↗
PubMed1991

Determination of hepatitis B virus DNA in serum using the polymerase chain reaction: clinical significance and correlation with serological and biochemical markers.

Sera from 98 patients with various stages of chronic hepatitis B virus infection were studied to determine the clinical significance of hepatitis B virus DNA in serum detected by the polymerase chain reaction. Patients were divided into three groups according to their HBsAg and HBeAg status. Group I (n = 31) had detectable HBsAg and HBeAg, group II (n = 46) had HBsAg but not HBeAg and group III (n = 21) consisted of patients who were once chronic hepatitis B virus carriers but had lost HBsAg during follow-up. Group I patients usually had significant liver disease (raised serum aminotransferases), had higher titers of HBsAg and had been infected with hepatitis B virus for a shorter period than patients in the other two groups. All patients in group I had hepatitis B virus DNA detectable by polymerase chain reaction and 94% had sufficient hepatitis B virus DNA present for detection by dot-blot hybridization. Group II patients had lower mean serum aminotransferase activities and titers of HBsAg than those in group I. Serum hepatitis B virus DNA was detectable by polymerase chain reaction in 78% but in only 30% of group II patients by dot-blot hybridization. Group II patients who did not have hepatitis B virus DNA detectable by polymerase chain reaction had mean serum aminotransferase levels within the normal range and had a younger mean age than those with hepatitis B virus DNA. Group III patients generally had no evidence of active liver disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

Gamma-aminobutyric acid (GABAA) receptor-function in a rat model of hepatic encephalopathy.

The functional activity of the gamma-aminobutyric acid (GABAA) receptor-chloride ionophore complex was studied in rats with hepatic encephalopathy (HE) secondary to thioacetamide-induced fulminant hepatic failure (FHF). Muscimol stimulation and benzodiazepine potentiation of GABA receptor-mediated 36Cl- uptake into cerebral cortical synaptoneurosomes was compared in HE and control rats. [3H]Flumazenil binding assays were conducted to determine whether the levels of endogenous benzodiazepine-like ligands in extracts of cortex were increased with stages of encephalopathy in this animal model of HE. In both control and HE rats maximal uptake of 36Cl- via the GABAA receptor complex occurred at muscimol concentrations of 30 microM. Potentiation of muscimol-stimulated 36Cl- uptake into synaptoneurosomes by diazepam (5 microM) was equivalent in both groups. Aqueous extracts of proteolytically digested homogenates of cerebral cortices prepared from control and HE rats were effective in stimulating 36Cl- uptake into synaptoneurosomes. Alkaline organic extracts of proteolytically digested homogenates of cerebral cortices from HE rats were more effective than corresponding extracts from controls at inhibiting the binding of [3H]flumazenil. Inhibition of [3H] fumazenil binding by organic extracts derived from the cerebral cortices of HE rats did not increase with progression of encephalopathy. The results show that muscimol-stimulated 36Cl- uptake into synaptoneurosomes and, consequently, GABAA receptor-mediated chloride channel function are not significantly altered in the model of HE studied and are consistent with the hypothesis that HE results in an increased availability of one or more endogenous ligands which can augment GABA receptor-gated chloride conductance.

Animals↗
PubMed1990

The effects of behavioral parent training on families with young hyperactive children.

We sought to assess, through two case-studies, the strengths and limitations of a time-limited, family-based behavioral intervention for preschool-aged children with attention-deficit-hyperactivity disorder (ADHD). The families completed a ten week child management training program and attended a number of follow-up sessions. Changes in parent and child functioning were assessed with a variety of rating scales, interviews, and data collected by parents at home on targeted behavior problems. Improvements were found in parents' confidence in their child management ability and knowledge of behavioral principles, in certain child behavior problems, in parental ratings of hyperactivity, and in the parent-child relationship. Implications of the findings for the treatment of young children with hyperactivity are discussed.

Attention Deficit Disorder with Hyperactivity↗