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Biomedical subjects

H A Pohl

Publications and source records attributed to H A Pohl.

11 recordsLinked to original sources
PubMed1990

Effects of melatonin and progesterone administered to ewes in spring and summer.

Melatonin (MEL) was evaluated for effects on LH, prolactin (PRL) and fertility in spring (Exp. 1, 2) and summer (Exp. 3 to 5). In Exp. 1, 17 ovariectomized ewes bearing estradiol implants were fed 3 mg MEL or vehicle for 44 d beginning May 1. Melatonin decreased (P less than .001) PRL levels but had no effect on LH secretion and response to GnRH. In Exp. 2, 12 ewes each received a 40-d MEL ear implant or a sham implant on March 31. Progesterone-releasing pessaries (CIDR) were applied for 12 d and were withdrawn concomitant with ram joining on May 7. Neither treatment stimulated follicular development or induced estrus or ovulation. Exp. 3 and 4 were contemporary 2 x 2 factorial trials with 24 ewes at each of two locations. Melatonin implants were administered on June 29 and CIDR on July 22. The CIDR were removed and rams (Exp. 3, vasectomized; Exp. 4, fertile) were joined on August 3. Days from introduction of rams to estrus were reduced (P less than .05) by CIDR but not by MEL. All ewes lambed in Exp. 4, and days to estrus and conception were reduced (P less than .001) by CIDR but not by MEL. Exp. 5 was designed like Exp. 4 except that MEL implants were inserted June 20 and rams were joined August 8. Intervals from introduction of rams to estrus were reduced (P less than .01) by both MEL and CIDR treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Anestrus↗
PubMed1985

The ac field patterns about living cells.

The presence of the small ac electric fields produced by living cells is shown by the gentle dielectrophoretic force on tiny dielectric particles. The beauty of the field patterns is made evident as the cell and particles settle in a hanging drop. Patterns characteristic of repulsion and of attraction, as well as of a dipolar and quadripolar nature, are observable.

Animals↗
PubMed1979

Continuous dielectrophoretic separation of cell mixtures.

Use of stream-centered dielectrophoresis (1-4) produced continuous separations on three cell mixtures (1) Chorella vulgaris with Netrium digitus, (2) Ankistrodesmus falcatus with Staurastrum gracile, and (3) Saccharomyces cerevisiae with Netrium digitus. Maximal separations were obtained for these mixtures of live cells at 100 kHz, 600 kHz, and 2.0 MHz, respectively. The technique was restricted to a frequency range of 0.01-32 MHz, and to suspensions of low conductivity in which microorganisms such as these algae and yeast are tolerant. Extension, however, to cellular organisms requiring higher osmolarity is readily feasible through the use of nonionic solutes such as sucrose, mannose, glycine, etc.

Cell Separation↗
PubMed1977

Electron spin resonance absorption of tissue constituents.

The electron spin resonance spectra at g = 2 of the structural and soluble proteins of mouse liver have been investigated separately. The structural materials have signals an order of magnitude stronger. Radicals with important similarities to those occurring in natural tissue can be induced by treating casein with methylglyoxal or crotonaldehyde. The structural proteins of cancer give little or no signal. The color of the proteins and their electron spin resonance signal seem closely related.

Animals↗
PubMed1971

Dielectrophoresis of cells.

Dielectrophoresis, the motion produced by the action of nonuniform electric field upon a neutral object, is shown to be a simple and useful technique for the study of cellular organisms. In the present study of yeast (Saccharomyces cerevisiae) using a simple pin-pin electrode system of platinum and high-frequency alternating fields, one observes that the collectability of cells at the electrode tip, i.e. at the region of highest field strength, depends upon physical parameters such as field strength, field uniformity, frequency, cell concentration, suspension conductivity, and time of collection. The yield of cells collected is also observed to depend upon biological factors such as colony age, thermal treatment of the cells, and chemical poisons, but not upon irradiation with ultraviolet light. Several interesting side effect phenomena coincident with nonuniform electric field conditions were observed, including stirring (related to "jet" effects at localized electrode sites), discontinuous repulsions, and cellular rotation which was found to be frequency dependent.

2,4,5-Trichlorophenoxyacetic Acid↗