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Biomedical subjects

H A Walker

Publications and source records attributed to H A Walker.

15 recordsLinked to original sources
PubMed2001

The phytoestrogen genistein produces acute nitric oxide-dependent dilation of human forearm vasculature with similar potency to 17beta-estradiol.

BACKGROUND: Genistein, a phytoestrogen, may have estrogenic cardioprotective actions. We investigated whether genistein influences endothelium-dependent vasodilation in forearm vasculature of healthy human subjects and compared the effects of genistein with those of 17beta-estradiol. METHODS AND RESULTS: The brachial arterial was cannulated with a 27-gauge needle for drug infusion. Forearm blood flow responses were measured with strain-gauge plethysmography. Genistein (10 to 300 nmol/min, each dose for 6 minutes) produced a dose-dependent increase in forearm blood flow from 3.4+/-0.3 to 9.6+/-1.3 mL x min(-1) x 100 mL forearm(-1) (mean+/-SEM) in men (n=9, P:<0.0001 by ANOVA). The mean forearm venous concentration of genistein during infusion of the highest dose was 1.8+/-0.3 micromol/L in 6 additional men. Genistein produced a similar increase in blood flow in premenopausal women. Daidzein, another phytoestrogen, was ineffective, but equimolar concentrations of 17beta-estradiol caused similar vasodilation to genistein. Responses to genistein and 17beta-estradiol were inhibited to the same degree by the NO synthase inhibitor N:(G)-monomethyl-L-arginine. A threshold dose of genistein potentiated the endothelium-dependent vasodilator acetylcholine but not the endothelium-independent vasodilator nitroprusside. CONCLUSIONS: Genistein causes L-arginine/NO-dependent vasodilation in forearm vasculature of human subjects with similar potency to 17beta-estradiol and potentiates endothelium-dependent vasodilation to acetylcholine.

Acetylcholine↗
PubMed2001

Endothelium-dependent vasodilation is independent of the plasma L-arginine/ADMA ratio in men with stable angina: lack of effect of oral L-arginine on endothelial function, oxidative stress and exercise performance.

OBJECTIVES: This study was designed to determine the effect of two weeks' treatment with L-arginine on the ratio of plasma L-arginine to asymmetric dimethylarginine (ADMA), oxidative stress, endothelium-dependent vasodilatation to acetylcholine, exercise performance and heart rate variability in men with stable angina. BACKGROUND: The ratio of plasma L-arginine:ADMA has been proposed as a determinant of endothelium-dependent dilation; dietary supplementation with L-arginine has been shown to improve endothelium-dependent vasodilation and symptoms in some conditions. METHODS: Men (n = 40) with stable angina, at least one epicardial coronary artery with a stenosis >50% and a positive exercise test were randomized to receive L-arginine (15 g daily) or placebo for two weeks according to a double-blind parallel-group design. Plasma L-arginine, ADMA, 8-epi-prostaglandin F2alpha (a marker of oxidative stress) and forearm vasodilator responses to brachial artery infusion of nitroprusside and acetylcholine (+/-L-arginine) were measured. A standard Bruce protocol exercise test was performed before and at the end of the treatment period. RESULTS: Plasma L-arginine increased after oral L-arginine, whereas ADMA remained unchanged, leading to an increase in the L-arginine/ADMA ratio of 62 +/- 11% (mean +/- SE, p < 0.01). Despite a significant enhancement in acetylcholine response by intra-arterial L-arginine at baseline, this response remained unchanged after oral L-arginine. Measures of oxidative stress and exercise performance after L-arginine/placebo were similar in placebo and active groups. CONCLUSIONS: In men with stable angina, an increase in plasma L-arginine/ADMA ratio after two weeks' oral supplementation with L-arginine is not associated with an improvement in endothelium-dependent vasodilatation, oxidative stress or exercise performance.

Administration, Oral↗
PubMed2001

Assessment of forearm vasodilator responses to acetylcholine and albuterol by strain gauge plethysmography: reproducibility and influence of strain gauge placement.

AIMS: To determine the within-subject reproducibility of the forearm blood flow response to acetylcholine and the beta2-adrenoceptor agonist albuterol as measured by strain gauge plethysmography. To examine the influence of strain gauge placement on these responses. METHODS: Vasodilator response to brachial artery infusion of drugs was assessed by strain gauge plethysmography in six healthy men on each of three occasions separated by 1 week. Strain gauges were placed on both arms at the point of maximum diameter. On the infused arm two further gauges were positioned approximately 4 cm proximal and distal to the middle gauge. RESULTS: Within-subject coefficients of variation (WCV) of absolute blood flow responses for each dose of acetylcholine (7.5, 15, 30 micrograms min(-1)) ranged from 24% to 27%, as compared with WCV values of 41% to 62% for the percentage changes in blood flow ratio (infused : noninfused arm). For albuterol (0.3, 1, 3 micrograms min(-1)) the corresponding WCV values were 16% to 19% and 30% to 55% for absolute blood flow and percentage change in blood flow ratio, respectively. WCV for the area under dose-response curve (AUC) for absolute blood flow was 18% and 13% for acetylcholine and albuterol, respectively. Vasodilator responses were similar whether recorded proximal to or at the point of maximal forearm circumference. Distal strain gauge misplacement underestimated responses and the difference was greater for acetylcholine than for albuterol. CONCLUSIONS: In healthy men, the WCV for responses expressed as absolute blood flow, to acetylcholine and albuterol ranges from 16% to 27%.

Acetylcholine↗
PubMed1979

Transformational deficits in cognition of schizophrenic children.

This study examined schizophrenic children for cognitive deficits in logical thinking, symbolic imagery, and conservation. Evaluation revealed persistent failure of the aberrant subjects to achieve at the level of age expectancy. Comparison with nonpsychotic, institutionalized children demonstrated no effect due to institutionalization. By mid-teens not one of the subjects had accomplished formal operations and very few were able to master concrete operations. Implications for development and treatment were discussed.

Adolescent↗
PubMed1977

Permeability of the mitochondrial membrane to bicarbonate ions.

Osmotic-swelling techniques show that HCO3- enters mitochondria by an electrogenic process, effectively HCO3- uniport, under non-energized conditions. This mode of translocation accounts for previous reports of non-entry of HCO3- in experiments with energy-linked Ca2+ uptake. The effects of HCO3- on mitochondrial respiration are reported and discussed.

Animals↗
PubMed1977

A dermatoglyphic study of autistic patients.

Dermatolglyphic patterns of autistic children were compared to those of control subjects matched socioeconomically and by age and sex. Analysis of dermal ridge patterns and ridge counts resulted in significant differences between the 78 autistic and 78 normal children. Differences from normal expectation in the autistic children were most apparent in the reduced number of whorls and increased number of arches, in lowered ridge counts, and in less distinctness in formation of ridge line. The number of dermal ridges on autistic hands was much lower for each finger as well as for the total hand. Moreover, covariance of the contribution of increased numbers of arches failed to alter the significance of findings of general reduction of ridge count in the autistic sample. Other abnormalities of ridge structure among the autistics were noted and described. Complete absence of transverse crease in this sample was combined with other dermatoglyphic evidence to argue for the separateness of autism from other pathological syndromes. It was concluded that evidence was sufficient to indicate the existence of congenital factors in the etiology of autism.

Adolescent↗
PubMed1977

Incidence of minor physical anomaly in autism.

Children diagnosed as autistic were matched by age and sex with 74 control subjects and examined for presence of minor physical anomalies. Of the 16 anomalies scored, autistic children demonstrated a significant accumulation greater than the number exhibited by normal children. Three of the stigmata--low seating of ears, hypertelorism, and syndactylia--were expressed differentially in the two groups, and high palate as well as unusual cranial circumference were significantly high in both groups. Clusters of stigmata that might be associated with known chromosomal disorders could not be identified. The increased number of anomalies suggests that among autistic children such congenital markers indicate a deviant intrauterine experience.

Abnormalities, Multiple↗
PubMed1976

Catechol-O-methyltransferase activity in psychotic children.

Catechol-O-Methyltransferase (COMT) activity was studied in three groups of institutionalized children: (1) a group of schizophrenic children; (2) a heterogeneous group of chronic psychotic children characterized by severe symptomatology and onset before 5 years of age; (3) a group of acting-out but nonpsychotic children. Erythrocyte COMT activity was found to be significantly lower among the schizophrenic subjects in contrast to the greater activity in both the other groups--the nonpsychotic and chronic psychotic children. The difference in COMT activity between psychotic groups appeared to be related to diagnosis and age of onset of disorder. Generality of findings is limited by the small sample size (N = 42) and by the difficulties inherent in the diagnosis of severe mental disorder in children. However, this preliminary study suggests that enzymatic activity may be associated with the development of schizophrenia in children.

Adolescent↗
PubMed1975

Concept usage in schizophrenic children.

This study compares concept usage and categorizing behavior among schizophrenic, normal, and brain-damaged children. Two sets of tasks were administered to each subject, the child being required to match an index object with one of a group of three choice objects. On the first task, the choice objects were related to the index object by class, function, or stimulus similarity; on the second task, the two choice objects were unrelated to the index object, while the remaining choice object was related by class or function. For both tasks the subjects were asked to state which of the choice objects was related to the index object, and why. Results indicated that the schizophrenic, normal, and brain-damaged children showed a significant improvement with increased age in utilizing class or function concepts. However, the schizophrenics, unlike the normal and brain-damaged children, did not benefit consistently from a reduction in stimulus competition. Within the schizophrenics, grouping by IQ revealed a dichotomous type of concept usage. Low IQ patients performed like the brain-damaged group; high IQ children failed to benefit from reduction in stimulus competition and produced more bizarre and irrelevant responses.

Age Factors↗
PubMed1975

Symptom formation as an expression of disordered information processing in schizophrenic children.

The possible mechanisms that underlie symptom formation in childhood schizophrenia are discussed. A body of research evidence has been reviewed in which dissociation in relation to information processing was examined for its possible consequence in the formation and expression of symptomatology. Schizophrenic children have been found to exhibit dissociation of integrative processes among the sense systems at a level which is several years below normal expectation, and they usually fail to improve as age increases. The clinical manifestations of schizophrenia are considered to be the consequence of the conflict, distortion, and deprivation that derive from failure in information processing. These consequences can best be understood within a developmental framework which encompasses the different age-stages of function. This approach to the understanding of symptom formation is discussed in relationship to other evidence which suggests that primary neurological abnormality is present in schizophrenic children. Thus the identification of abnormality of intersensory integrative function may increase our understanding of etiology as well as of the mechanisms of symptom formation in schizophrenic children.

Attention↗