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Biomedical subjects

H Oshima

Publications and source records attributed to H Oshima.

At least 343 records · Page 19Linked to original sources
PubMed1975

EEG correlates of impaired attention performance under secobarbital and chlorpromazine in the monkey.

The effects of secobarbital and chlropromazine upon behavior in a continuous, rapidly presented successive (go-no go) discrimination ("attention") task were evaluated in six Macaca mulatta monkeys. Simultaneous monitoring of EEG activity from epidural and subcortical electrodes permitted an evaluation of the nature of altered central nervous system events during erroneous performance (errors of omission) on this task. The computer-assisted analysis of pre-stimulus and post-stimulus EEG frequency activity (baseline crossings) suggests that the best measure of attentive behavior from the pre-stimulus EEG is percentage of beta 2 (25-40 cps) activity. No difference could be observed between drugs or among cerebral placements in this regard. This was determined by comparing measures of EEG frequency, pooled for a given test period, with performance from the same test period. On a trail-by-trail basis. however, the beta 2 measure in the pre-stimulus epoch failed to ditinguish correct responses from errors of omission. Separation between correct responses and errors of omission is possible if comparisons are made between the changes in percentage of beta 2 activity in the pre-stimulus vs. post-stimulus occurs with correct positive trials and the smallest change with correct negative trials. For secobarbital, no difference could be detected between correct and incorrect positive trials. For chlorpromazine, however, there was significantly less change in beta 2 for incorrect positive than for correct positive trials. The results were interpreted in terms of the hypothesis that secobarbital produces errors by depression of the general level of activation whereas chlorpromazine acts by reducing the sensory input which is necessary for correct discrimination performance.

Animals↗
PubMed1975

Studies on the human testis. VI. NADH-linked reactions of microsomal steroid 20alpha-and 20beta-hydroxysteroid dehydrogenase and 17alpha-hydroxylase.

NADH-linked 20alpha- and 20beta-hydroxysteroid dehydrogenase and 17alpha-hydroxylase activities were demonstrated in the microsomal fraction of the human testis. The microsomal 20alpha-hydroxysteroid dehydrogenase showed substrate affinity to pregnenolone and progesterone and not to 17alpha-hydroxyprogesterone and preferred NADH to NADPH as a hydrogen donor. In the presence of NADH, the optimal pH for the enzyme was 7.7 and the apparent Michaelis constants of the enzyme for progesterone and pregnenolone at 37 C and pH 7.4 were 6.9-7.1 X 10-6M and in the order of 10-5M, respectively, 17alpha, 20beta-Dihydroxypregn-4-en-3-one was the only significant metabolite produced from 17alpha-hydroxyprogesterone by microsomal fraction of the human testis in the presence of NADH. The apparent Michaelis constant of microsomal 20beta-hydroxysteroid dehydrogenase for 17alpha-hydroxyprogesterone in the presence of NADH was in the order of 10-5M at 37 C and pH 7.4. The microsomal 17alpha-hydroxylase catalyzed the metabolism of pregnenolone and progesterone at a similar rate in the presence of NADH. The optimal pH and the apparent Michaelis constant at 37 C and pH 7.4 of the NADH-linked reaction of 17alpha-hydroxylase for progesterone were 7.7 and 5.3-5.4 X 10-7M, resepctively. The NADH-linked enzyme activity for progesterone was competitively inhibited by both pregn-5-ene-3beta, 20alpha-diol (inhibition constant: 1.7 X 10-7M) and 20alpha-hydroxypregn-4-en-3 one (inhibition constant: 6.6 X 10-7M), and was resistant to poor oxygen supply during incubation. The results indicate that the microsomal 20alpha-hydroxysteroid dehydrogenase is a different enzyme from the one in the soluble fraction of the human testis and that microsomal 17alpha-hydroxylase in the human testis is activated by NADH as well as NADPH.

Binding, Competitive↗
PubMed1975

Studies of the human testis. V. Properties of delta-5-3beta and 17beta-hydroxysteroid dehydrogenases in the biosynthesis of testosterone from dehydroepiandrosterone.

The properties of delta-5-3beta-hydroxysteroid dehydrogenase and 17beta-hydroxysteroid dehydrogenase in the human testis were examined using cell-free homogenates with added cofactors. Michaelis constants of the delta-5-3beta-hydroxysteroid dehydrogenase enzyme at 37 C and pH 7.4 were 8.2 times 10 minus 7M for dehydroepiandrosterone and 2.9 times 10 minus 6M for androstenediol. The optimal pH for both substrates was approximately 8.15. Dehydroepiandrosterone and androstenediol are competitive substrates for the enzyme. When free and conjugated C19 steroids in the order of 10 minus 6 were added, androstenedione and testosterone inhibited the enzyme activity for dehydroepiandrosterone while the activity for androstenediol was inhibited by addition of dehydroepiandrosterone and its sulfate as well as by androstenedione and testosterone. 17beta-Hydroxysteroid dehydrogenase had two apparent Michaelis constants for dehydroepiandrosterone, 3.3 times 10 minus 6M at low substrate concentrations and 1 times 10 minus 5M at high substrate concentrations. The enzyme activities for dehydroepiandrosterone and androstenedione were found to be enhanced by addition of the 17beta-hydroxysteroids examined and slightly inhibited by addition of dehydroepiandrosterone-sulfate and androstenediol-3-monosulfate. Androstenedione caused an inhibition of the 17beta-hydroxysteroid dehydrogenase for dehydroepiandrosterone. The interconversion between androstenedione and testosterone by the enzyme favored testosterone formation. Following simultaneous incubation of 3H-dehydroepiandrosterone and 14C-androstenediol in equal amounts, initially more testosterone was produced from dehydroepiandrosterone than from androstenediol under the conditions employed, while subsequently with accumulation of androstenediol more testosterone was produced from androstenediol.

Aged↗