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Biomedical subjects

A L Schmidt

Publications and source records attributed to A L Schmidt.

At least 19 recordsLinked to original sources
PubMed2000

Meiotic competence in horse oocytes: interactions among chromatin configuration, follicle size, cumulus morphology, and season.

Horse oocytes were collected from an abattoir over a 15-mo period. After classification of follicle size and cumulus morphology, oocytes were either fixed immediately (0 h) or matured in vitro (24 h). There was no effect of season on the number of antral follicles present on the ovaries, or on oocyte maturation rate for any class of oocyte. The proportion of oocytes having condensed chromatin at 0 h increased with increasing follicle size. The oocyte maturation rate also increased with follicle size, and for follicles </= 20-mm diameter, was higher for oocytes initially having expanded cumuli than for those having compact cumuli. The maturation rate was strongly correlated (r(2) = 0.92) with the proportion of oocytes having condensed chromatin at 0 h. Oocytes with diffuse chromatin were found essentially only in follicles </= 20-mm diameter that yielded compact granulosa, indicating follicle viability. Presence of diffuse chromatin was inversely related to maturation rate. We conclude that the major signal for chromatin condensation, and thus acquisition of meiotic competence, occurs in viable follicles after 20-mm diameter in the horse. Condensation of chromatin in oocytes in smaller apparently viable follicles, while associated with acquisition of meiotic competence, may represent a pre-atretic change.

Animals↗
PubMed1995

Effect of follicular components on meiotic arrest and resumption in horse oocytes.

Two experiments were conducted to evaluate the effect of follicular components on the maintenance of meiotic arrest in horse oocytes. In Expt 1, oocytes were incubated for 24 h with follicular fluid, or with granulosa cells suspended either in medium or in follicular fluid at 25 x 10(6) cells ml-1. None of the treatments resulted in significant maintenance of the germinal vesicle stage over that of non-suppressive control. Culture with follicular fluid plus granulosa cells resulted in a significantly higher proportion of oocytes at metaphase I compared with controls. In Expt 2, oocytes were divided into those originally having compact or expanded cumuli. Oocytes were cultured with sheets of mural granulosa or sections of follicle wall, or after injection into intact dissected follicles. After incubation, half of the oocytes from each suppressive treatment were matured for 24 h. All three suppressive treatments were effective in maintaining oocytes at the germinal vesicle stage (no significant difference from control oocytes fixed directly after removal from the follicle). However, no treatment maintained normal viability of oocytes, as significantly fewer oocytes were at metaphase II after all the suppression-maturation treatments compared with the maturation control. The highest rate of post-suppression maturation was found in the mural granulosa treatment. Within this treatment, the proportion of oocytes in metaphase II was significantly higher for oocytes with expanded than for oocytes with compact cumuli (31% versus 11%, respectively; P < 0.05). Suppression by injection into an intact follicle was associated with a lack of progression to metaphase II during subsequent maturation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Reversal of the red beet tonoplast H(+)-ATPase by a pyrophosphate-generated proton electrochemical gradient.

The reversal of the tonoplast H(+)-ATPase to mediate ATP synthesis was investigated in tonoplast vesicles isolated from red beet (Beta vulgaris L.) storage tissue. Our approach involved use of the H(+)-PP(i)ase to establish a proton electrochemical gradient (delta muH+) across the tonoplast vesicle membrane to drive the H(+)-ATPase in reverse. However, an initial problem with this approach was the presence of an adenylate kinase activity in the tonoplast fraction that interfered with measurement of ATP synthesis as a coupling between the H(+)-ATPase and H(+)-PP(i)ase. Inclusion of the adenylate kinase inhibitor p1p5-di(adenosine)pentaphosphate (Ap5A) in assays at 50 microM led to a complete inhibition of this activity and allowed measurement of ATP synthesis coupled to PPi hydrolysis. When measured in the presence of Ap5A, PPi-dependent ATP synthesis was blocked by Triton X-100 and inhibited by gramicidin D, imidodiphosphate, nitrate, and bafilomycin A. These results are consistent with PPi-dependent ATP synthesis occurring as a coupled process involving a delta muH+ established across the membrane. Furthermore, the observation that ATP synthesis is inhibited by inhibitors of the tonoplast H(+)-ATPase (nitrate and bafilomycin A) would suggest that this enzyme is involved in the synthetic reaction and can operate in reverse to synthesize ATP from ADP and Pi. A thermodynamic analysis of coupling between the H(+)-PP(i)ase and H(+)-ATPase suggests that PPi-driven ATP synthesis could only occur under these reaction conditions if the H+/substrate stoichiometries for the H(+)-PP(i)ase and H(+)-ATPase were 1 and 2, respectively. These values are consistent with transport stoichiometries previously determined for these enzymes in red beet tonoplast vesicles using kinetic methods.

Adenosine Triphosphate↗
PubMed1993

Energy transduction in tonoplast vesicles from red beet (Beta vulgaris L.) storage tissue: H+/substrate stoichiometries for the H(+)-ATPase and H(+)-PPase.

The H+/substrate stoichiometries of the tonoplast H(+)-ATPase and H(+)-PPase were determined by a kinetic approach. Using red beet (Beta vulgaris L.) tonoplast vesicles, rates of substrate-dependent H+ transport were estimated by (I) a mathematical model describing the time course of delta pH formation, (II) the rate of H+ leakage following H+ pump inhibition at a steady state delta pH, and (III) the initial rate of alkalinization of the external medium. When compared with rates of substrate hydrolysis measured under identical conditions, all three methods yielded an H+/ATP stoichiometry of 2 while the H+/PPi stoichiometry was determined to be 1 using methods I and II. Experimental limitations did not permit an analysis of the H+/PPi stoichiometry by method III. From these results and the estimated level of substrate and product typically found in the cytoplasm of plant cells, it is suggested that the H(+)-ATPase and H(+)-PPase as primary H(+)-pumps are poised toward net substrate hydrolysis under in vivo conditions thereby operating in parallel to generate a proton electrochemical gradient across the tonoplast.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1993

In vitro maturation of horse oocytes: characterization of chromatin configuration using fluorescence microscopy.

The chromatin configuration of resting horse oocytes and the time course of in vitro oocyte maturation was characterized using a fluorescent, DNA-specific label. Oocytes were classified as having either compact (CP) or expanded (EX) cumuli at the time of collection. Centrifugation of oocytes was effective in allowing visualization of the germinal vesicle. Two main chromatin configurations were found in oocytes known to have a germinal vesicle: condensed chromatin (CC), in which the chromatin formed a dense mass surrounding the nucleolus; and fluorescing nucleus (FN), in which the entire nucleus, containing diffuse or spotty chromatin, was visible. The proportion of CC to FN was higher for oocytes with EX cumuli. At time 0, 78% of CP oocytes and 73% of EX oocytes were in the germinal vesicle stage. Significantly more EX than CP oocytes were in metaphase I or II at time 0. In both CP and EX groups, maturation had not begun after 8 h of incubation. Maximal maturation occurred after 24 h for oocytes in the EX group, whereas CP oocytes continued to mature between 24 and 32 h. The percentage of EX oocytes in metaphase I did not change between 24 and 32 h, indicating a possible arrest of some EX oocytes at metaphase I. There was no difference in the percentage of oocytes at metaphase II between the CP and EX groups after 32 h of incubation.

Animals↗
PubMed1988

Larval development test for detection of anthelmintic resistant nematodes.

The growth, using freshly cultured Escherichia coli with ampicillin or heat-treated lyophilised E coli as a food source, of the larvae of the mouse nematode Nematospiroides dubius and the infectivity of resulting third stage larvae were determined. Concentrations of E coli between 0.5 and 1 mg dry weight ml-1 permitted optimal larval development for both N dubius and Trichostrongylus colubriformis. Development of larvae of susceptible and cambendazole-resistant strains of Haemonchus contortus in thiabendazole solutions showed clear differences between the strains and the larval development test was more sensitive than the egg hatch test. The test also detected a levamisole resistant strain of H contortus, although the degree of resistance could not be adequately measured. It is concluded that the test can be run with any anthelmintic to which resistance is suspected.

Animals↗
PubMed1985

Germicidal persistence of teat dips by modified excised teat procedure.

An excised teat protocol was modified to evaluate persistence of germicidal activity of teat dips over 8 h. Five teat dip formulations, iodophor (1%), chlorhexidine gluconate (.55%), linear dodecyl benzene sulfonic acid (1.94%), sodium chlorite-lactic acid in a water base, and sodium chlorite-lactic acid in a gel base were tested against Escherichia coli and Klebsiella oxytoca. Iodophor and chlorhexidine had high germicidal activity throughout 8 h, whereas dodecyl benzene sulfonic acid had little activity. Germicidal activity of both sodium chlorite-lactic acid teat dips was high initially but declined with time. The gel base dip, however, remained more germicidal than the water base dip. Results were similar for either organism for most teat dips. However, chlorhexidine was less effective and the gel base dip more effective against Klebsiella oxytoca than Escherichia coli. Standard errors often appeared higher for Klebsiella oxytoca than for Escherichia coli. These assays may prove useful for laboratory screening of teat dips to determine germicidal persistence over time.

Animals↗
PubMed1984

Evaluation of experimental teat dip containing sodium chlorite and lactic acid by excised teat assay.

An experimental teat dip containing sodium chlorite and lactic acid, diluted in water, was evaluated by excised teat protocol. The teat dip was tested against 21 microorganisms. Included were: Staphylococcus aureus, Streptococcus agalactiae, Streptococcus dysgalactiae, Streptococcus uberis, Escherichia coli, Klebsiella oxytoca, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Numerous strains were tested for strain differences. Environmental bacteria were included because of their increasing importance as a cause of bovine mastitis. All excised teats were dipped in a bacterial suspension containing about 1 X 10(8) cfu/ml. Negative control teats were not dipped in a germicidal compound. Positive controls were dipped in 1% iodophor. Effectiveness of the experimental teat dip was expressed as the percent reduction in mean log of bacteria recovered from dipped teats as compared to numbers recovered from control teats. The sodium chlorite - lactic acid dip caused a greater percent log reduction than iodophor for 14 of 21 strains tested. However, differences were generally slight. The experimental teat dip appeared effective against Gram-negative bacteria. Some differences in percent log reduction were observed between strains of the same species. Lowest effectiveness and greatest strain variation were observed with Staphylococcus aureus for both dips tested.

Animals↗
PubMed1983

Cerebral activation patterns in an arithmetic and a visuospatial processing task.

Evoked potentials (EPs) to a probe tone stimulus were recorded simultaneously at the temporal and parietal areas of the left and right hemisphere of dextral adults engaged in either an arithmetic or a visuospatial task. The probe EP amplitude was attenuated in the left temporal area during the arithmetic task and in the left temporal and both parietal areas, but significantly more in the right, during the visuospatial task, indicating distinct patterns of regional cerebral engagement for the two types of cognitive activity.

Adult↗
PubMed1975

Determination of acetaminophen in pharmaceutical preparations and body fluids by high-performance liquid chromatography with electrochemical detection.

A sensitive and very rapid assay for acetaminophen was developed based on the combination of high-performance chromatographic columns with a thin-layer electrochemical detector. Application to liquid and solid dosage forms and body fluids has been demonstrated. Great advantage derives from the detector selectivity, which permits discrimination against many potentially interfering substances without need for extensive separations or formation of derivatives. As little as 0.005% of the hydrolysis product, p-aminophenol, can be detected in the presence of the intact drug following cation-exchange chromatography. Acetaminophen can be quantitatively determined in serum on the 50-ng/ml level by liquid chromatography using a pellicular polyamide packing.

Acetaminophen↗