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Biomedical subjects

P Silberzahn

Publications and source records attributed to P Silberzahn.

At least 37 records · Page 2Linked to original sources
PubMed1988

[Urinary steroids in calves following administration of anabolic compounds. Effect of total diet].

Levels of testosterone, trenbolone, 17 beta-estradiol (conjugated plus unconjugated) and creatinine were measured in urine of calves treated 55 days before with trenbolone and 17 beta-estradiol implants. The mean concentration of urinary creatinine and implant steroids was increased by a factor 3 after 1 day of total diet and 5 after 2 days, levels of individual calves exhibiting a great dispersion.

Animals↗
PubMed1987

Aromatization of 19-norandrogens by equine testicular microsomes.

In the stallion testis, aromatase activity was localized in the microsomal fraction. Androgen aromatization occurred through the loss of 1 beta,2 beta hydrogen atoms and appeared to involve free sulfhydryl groups. A single enzyme system seemed to aromatize androgen and norandrogen at the same rate while having a much lower affinity for norandrogens.

Aging↗
PubMed1987

Characterization of equine plasma lipoproteins after separation by density gradient.

1. Plasma lipoproteins from six thoroughbred horses were separated by density gradient ultracentrifugation. For each sample, lipoprotein bands were visualized by means of a prestained plasma control and characterized by electrophoretic, chemical and morphological analysis. 2. Very low density lipoproteins (VLDL) were isolated at d less than 1.018 g/ml. 3. Two clearly resolved bands were detected in the low density lipoprotein fraction (LDL). The density limits were evaluated as follows: LDL1(1.028 less than d less than 1.045 g/ml) and LDL2(1.045 less than d less than 1.070 g/ml). Marked differences were observed in the chemical composition and particle size of LDL1 and LDL2 fractions. 4. High density lipoprotein fraction (HDL) was usually isolated as a single band, distributed over the range 1.075 less than d less than 1.180 g/ml. However, chemical composition and particle size revealed heterogeneity in HDL subfractions. 5. The density limit of LDL and HDL bands varied in each animal, indicating differences in equine lipoprotein distribution.

Animals↗
PubMed1985

Estrogen metabolites in equine ovarian follicles: gas chromatographic-mass spectrometric determinations in relation to follicular ultrastructure and progestin content.

Equine follicular fluid was aspirated at various developmental stages (viable, preovulatory and atretic) determined by ultrastructural study. Estrogens and progestins were analyzed by gas chromatography-mass spectrometry associated with stable isotope dilution. Progesterone and 17-hydroxyprogesterone were the principal progestins of the preovulatory and viable follicles. Among the catechol estrogens, 2-hydroxy-estradiol was particularly abundant in the preovulatory follicle and its definitive identification was made by the scan of a full mass spectrum.

Animals↗
PubMed1985

Gas chromatography-mass spectrometry of androgens in equine ovarian follicles at ultrastructurally defined stages of development. Identification of 19-nortestosterone in follicular fluid.

Follicular fluid was obtained from equine follicles at different stages of development as determined by ultrastructural study. Gas chromatography-mass spectrometry associated with stable isotope dilution permitted the demonstration of high levels of 4-estrene-3,7-dione and 17 beta-hydroxy-4-estren-3-one, 17 beta-hydroxy-4-estren-3-one levels often being about 10 times higher than those of testosterone. These findings suggest that in the mare ovary, an aromatizing pathway may proceed using these 19-norsteroids as intermediates. As a consequence of this high level of 19-norsteroids, testosterone content may be most often overestimated by RIA. RIA of steroids in follicular fluid should be validated by a reference technique based on gas chromatography-mass spectrometry, associated with stable isotope dilution.

Androgens↗
PubMed1985

Steroidogenic characteristics of the adrenal cortex of the mare studied by electron microscopy.

The three concentric zones of the horse adrenal cortex (zonae glomerulosa, fasciculata and reticularis) showed marked interpenetration and exhibited a different relative development according to their position in the gland. Whereas the three cortical zones each had a specific histological structure, the ultrastructure of their cells showed a certain qualitative homogeneity. The differences corresponded essentially to the relative abundance of the constituents which are generally considered typical of steroidogeneous cells: mitochondria with vesicular cristae, smooth endoplasmic reticulum and lipid droplets. Their importance increased progressively from the zona glomerulosa to the zona reticularis. In this zone, the presence of gap and septate-like cell junctions, and mitochondria with vesicular cristae in close proximity to a smooth endoplasmic reticulum with numerous dilated tubules, suggested that steroidogenesis may be the most active. Ultrastructural findings were indicative of only quantitative differences between the steroidogenic capacities of the three zones of the mare adrenal cortex.

Adrenal Cortex↗
PubMed1984

Androstenedione and testosterone biosynthesis by the adrenal cortex of the horse.

An homogenate from cortical tissue of mare adrenals was incubated in the presence of tritiated pregnenolone. The (3H) androstenedione and the (3H) testosterone synthesized during the incubation were extracted, purified, and co-crystallized to constant specific activity in the presence of unlabeled carriers. The rate of conversion of pregnenolone to androstenedione and testosterone was of the order of 5 and 0.15 per cent respectively. The high ratio of (3H) androstenedione to (3H) testosterone observed in this study suggests that androstenedione is the main androgen produced by mare adrenals. It is concluded that adrenals could contribute to the production of blood androgens in normal as well as hyperandrogenic mares.

Adrenal Cortex↗
PubMed1984

Concentration increase of unbound testosterone in plasma of the mare throughout pregnancy.

Blood testosterone levels were measured by RIA and gas chromatography-mass spectrometry in the pregnant mare. They were found to increase from the very beginning of pregnancy, reaching peak values 10 times higher than the basal values at the seventh month and then to return to basal values by the week after parturition. Testosterone binding by plasma proteins was investigated in nonpregnant and pregnant mares throughout gestation. Equilibrium dialysis and gel equilibration methods did not reveal any blood specific testosterone-binding activity at any gestational stage. Hence, blood testosterone increase cannot result as in the pregnant woman or guinea pig, from an increase in blood specific binding activity but more probably results from an increased steroid production. It is suggested that the maternal gonads would be responsible for the testosterone increase in early pregnancy, during the period of PMSG production, and the fetoplacental unit for the subsequent increase.

Animals↗
PubMed1983

Identification and measurement of testosterone in plasma and follicular fluid of the mare, using gas chromatography-mass spectrometry associated with isotope dilution.

Testosterone has been identified by mass spectrometry in blood and follicular fluid aspirated from mature Graafian follicles of mares. Quantitative measurements made by gas chromatography-mass spectrometry have validated the determination of plasma testosterone made by radioimmunoassay. However, because of high levels of epitestosterone (17 alpha-hydroxyandrost-4-en-3-one) in the follicular fluid, radioimmunoassay overestimates the true concentrations of testosterone. The occurrence of testosterone in mare follicular fluid at a concentration which is two orders of magnitude higher than that in peripheral plasma suggests that the follicle may contribute to the production of circulating testosterone. A biosynthetic pathway for oestradiol-17 beta which involves testosterone is therefore likely to occur in the mare ovary as in many other mammalian species.

Animals↗