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961.
Reviewers for 1988 and 1989 相似文献
962.
963.
Roger A. Hoffman Peter Habeeb Gerald R. Buzzell 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1990,160(3):269-275
Summary Long-term increased or decreased circulating levels of thyroid hormones significantly modify porphyrin concentrations and morphology in the Harderian glands of male and female hamsters. Administration of T3 reduced porphyrin concentrations in females; this treatment or decreasing thyroid hormone levels with KClO4 suppressed the post-castration rise of porphyrins in males. Hypophysectomy led to increased porphyrins in the Harderian glands of males; this rise was suppressed in hypophysectomized males by T3 or T4. In females, hypophysectomy reduced porphyrins which were further reduced by daily administration of T3 or T4. These modifications in the normal females were identical in castrated males. Mitotic activity in the Harderian glands of females was stimulated by KClO4 and by hypophysectomy with or without exogenous T3. In males, castration increased mitotic activity which was suppressed by T3 and exacerbated by KClO4. Increased mitotic activity seemingly follows loss of tissue mass. The data show that thyroid hormones act directly on the Harderian glands rather than indirectly through modification of TSH synthesis/release. Female type glands in males are a consequence of loss of gonadal androgens by castration, or by suppression or loss of thyroid hormones by hypophysectomy or by treatment with KClO4. However, male type glands in females are the result of androgen treatment, and/or increased levels of thyroid hormones via reduced ambient temperatures or of photic input. We conclude that regulation of the Harderian gland appears to be different in the two sexes.Abbreviations
T
3
Triiodothyronine
-
T
4
Thyroxine
-
TSH
Thyroid Stimulating Hormone
-
KClO
4
Potassium Perchlorate
-
h
hours
-
ml
milliliter
-
mg
milligram
-
g
gram
-
male
-
female
-
castrated male
- AP
hypophysectomized
-
CON
Control
-
ALA
delta aminole-vulenic acid
-
HG
Harderian Gland 相似文献
964.
The hydrolytic activity of lipolytic enzymes in reverse micelles can be measured continuously with Fourier Transform infrared spectroscopy (FTIR) by following in the region of the OH-stretching band the water consumption during the reaction. This possibility is unique to reverse micellar solutions, because they are optically transparent and because they contain only a limited amount of water. 相似文献
965.
Dr. Edward B. Blanchard Peter J. Cornish David A. Wittrock Steve Fahrion 《Applied psychophysiology and biofeedback》1990,15(2):145-159
Reports of subjective experiences of 73 hypertensive patients who were treated with thermal biofeedback for hand warming were obtained over 16 treatment sessions. Most of the differential responding in subjective report occurred in the first 5 sessions. Differences in reports of throbbing were associated with medication status during treatment (presence of sympatholytic antihypertensive agent). From 4 to 9% of patients report negative subjective experiences at any one session. When short-term clinical successes (either elimination of medication or reduction of BP) were compared with short-term failures, it was found that successes reported more warmth, more likelihood of falling asleep, and more dreamlike experiences. The latter were more likely to occur suddenly for the successes. Correlational analyses revealed consistent positive associations between reports of warmth and relaxation with highest temperature achieved in the session and consistent negative associations between experiencing physical sensations and degree of temperature change within the session.This research was supported in part by grants from NHLBI, HL-27622 and HL-31189. 相似文献
966.
Angie Rizzino Peter Kazakoff John Nebelsick 《In vitro cellular & developmental biology. Plant》1990,26(5):537-542
Summary Previous studies have shown that cell density can regulate the binding of several growth factors. To determine whether cell
density exerts a uniform effect on the expression of epidermal growth factor (EGF) receptors, seven cell lines were examined
in detail. For each cell line, EGF binding was found to decrease as cell density increases. Scatchard analysis of the binding
data reveals that decreases in EGF binding are due to reductions in the number of cell surface EGF receptors. The only apparent
exception is the effect of cell density on the binding of EGF to A-431 cells. For these cells, increases in cell density lead
to two effects: decreases in the number of high affinity EGF receptors and increases in the total number of EGF receptors.
In addition to the effects of cell density on EGF receptors, it was determined that increases in cell density can coordinately
down-regulate receptors for as many as four different growth factors. Overall, the findings described in this report for EGF
and those previously described for transforming growth factor type-β (TGF-β) and fibroblast growth factor (FGF) demonstrate
the existence of a common mechanism for down-regulating growth factor receptors.
This work was supported by grants from the Nebraska Department of Health (89-51), the National Cancer Institute (Laboratory
Research Center Support Grant, CA36727), and the American Cancer Society (Core Grant ACS SIG-16).
EDITOR'S STATEMENT The paper by Rizzino et al. demonstrates that receptor number decreases as a function of cell density.
This may represent a mechanism by which cell proliferation is reduced as cell density increases. 相似文献
967.
Purified recA protein is induced by high salt concentrations to hydrolyse ATP even in the absence of DNA. By small angle neutron scattering we show that this salt activation results from a structural transition of the protein filament in the presence of ATPγS from the inactive, compact form (a helical polymer of pitch 70 Å and cross-sectional radius of gyration Rc 40 Å) to the open form (a helical filament of pitch 95 Å and Rc 35 Å, which are the same structural parameters as in the ATPase active complex with DNA and ATP), without detectable change in the degree of association. We conclude that activation of recA is due to the same structural change whether induced by the binding of DNA or by salt. Indeed, the other enzymatic activity of recA, the proteolytic cleavage of the lexA repressor, is found to be inducible by the same salt concentrations as those of the structural transition. 相似文献
968.
Serum-free culture of enriched mouse anterior and ventral prostatic epithelial cells in collagen gel
Timothy Turner Howard A. Bern Peter Young Gerald R. Cunha 《In vitro cellular & developmental biology. Plant》1990,26(7):722-730
Summary Sustained growth of mouse ventral and anterior prostatic epithelial cells embedded within collagen gel matrix was achieved
in a serum-free medium composed of Dulbecco's modified Eagle's medium and Ham's F12 medium, 1∶1 (vol/vol), supplemented with
bovine serum albumin fraction V, epidermal growth factor, transferrin, cholera toxin, prolactin, 5α-dihydrotestosterone, cortisol,
putrescine, fibroblast growth factor, and a trace element mixture. Three-dimensional growth of prostatic epithelial cells
occurred inside the collagen gel matrix. This serum-free medium allowed cell growth greater than sevenfold over 10 d in culture.
Tissue recombination and cell culture techniques were integrated to demonstrate that cultured cells retained prostatic characteristics.
Following 10 d of culture, epithelial colonies from mouse ventral and anterior prostatic epithelial cell cultures were isolated
and combined with rat fetal urogenital sinus mesenchyme and grown for 4 wk under the renal capsule of intact athymic male
mice. These tissue recombinants showed distinctive prostatic histologic characteristic (alveoli and ducts lined with cuboidal
or columnar epithelium surrounded by stroma). When histologic sections of recombinants were stained with the Hoechst 33258,
epithelial cells of mouse origin were distinguishable from stromal cells of rat origin.
Aided by grants CA-05388 and CA-09041 from the National Institutes of Health, Bethesda, MD, and by M. A. R. C. fellowship
GM08730 to T. T. 相似文献
969.
Our recent spin trapping studies of free radical generation by ultrasound in aqueous solutions are reviewed. The very high temperatures and pressures induced by acoustic cavitation in collapsing gas bubbles in aqueous solutions exposed to ultrasound lead to the thermal dissociation of water vapor into H atoms and OH radicals. Their formation has been confirmed by spin trapping. Sonochemical reactions occur in the gas phase (pyrolysis reactions), in the gas-liquid interfacial region, and in the bulk of the solution (radiation-chemistry reactions). The high temperature gradients in the interfacial regions lead to pyrolysis products from non-volatile solutes present at sufficiently high concentrations. The sonochemically generated radicals from carboxylic acids, amino acids, dipeptides. sugars, pyrimidine bases. nucleosides and nucleo-tides were identified by spin trapping with the non-volatile spin trap 3.5-dibromo-2.6-dideuterio-4-nitrosobenzenesulfonate. At low concentrations of the non-volatile solutes. the spin-trapped radicals produced by sonolysis are due to H atom and OH radical reactions. At higher concentrations of these non-volatile solutes, sonolysis leads to the formation of additional radicals due to pyrolysis processes (typically methyl radicals). A preferred localization of non-volatile surfactants (compared to analogous non-surfactant solutes) was demonstrated by the detection of pyrolysis radicals at 500-fold lower concentrations. Pyrolysis radicals were also found in the sonolysis of aqueous solutions containing only certain nitrone spin traps. The more hydrophobic the spin trap, the lower the concentration at which the pyrolysis radicals can be observed. The effect of varying the temperature of collapsing transient cavities in aqueous solutions of different rare gases and of N2O on radical yields and on cell lysis of mammalian cells was investigated. 相似文献
970.
Abstract. Patterns of plant succession were studied in areas of scorched and blown-down forest resulting from the 1980 eruption of Mount St. Helens, Washington. Changes in species abundance were observed for 7 years in permanent sample plots representing four post-disturbance habitats, or site types. Total plant cover and species richness increased with time on all site types. In blown-down forests supporting snowpack at the time of eruption, understory recovery was dominated by the vegetative regeneration of species persisting through disturbance. In forests without snowpacks, plant survival was poorer. Increases in cover and diversity were dominated first by introduced grasses, then by colonizing forbs characteristic of early successional sites. Epilo-bium angustifolium and Anaphalis margaritacea showed widespread recruitment and clonal expansion throughout the devastated area. As a result, species composition on previously forested sites converged toward that on formerly clearcut sites, where early serai forbs resprouted vigorously from beneath the tephra. Total plant cover and species diversity were poorly correlated with post-disturbance habitat and general site characteristics (e.g. distance from the crater, elevation, slope, and aspect). However, distributions of several life-forms (e.g. low sub-shrubs and tall shrubs) were strongly correlated with depth of burial by tephra and with cover of tree rootwads. Thus, early community recovery may reflect microsite variation or chance survival and recruitment rather than broad-scale gradients in environment or disturbance. Recovery of pre-disturbance composition and structure will undoubtedly be much slower than after other types of catastrophic disturbance. The rate and direction of community recovery will largely depend on the degree to which original understory species survived the eruption. 相似文献