Browsing by Author "Hoffmann, Bernd"
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Item Investigations into the mechanisms controlling parturition in cattle(Bioscientifica, 2012-08) Shenavai, Sima; Preissing, Susanne; Hoffmann, Bernd; Dilly, Marc; Pfarrer, Christiane; Schuler, Gerhard; Özalp, Gözde R.; Çalışkan, Çağlar; Seyrek, Kamil İntaş; Uludağ Üniversitesi/Veteriner Fakültesi/Doğum ve Jinekoloji Anabilim Dalı.; 0000-0003-4694-6937; AAH-7292-2019; AAE-3607-2019; 23985710500; 23984353800; 6603409870A pronounced increase in fetal cortisol concentrations stimulating an increase in estrogen production at the expense of progesterone precursors in the placenta, luteolysis, and progesterone withdrawal is considered as a key event during the complex signal cascade leading to the initiation of parturition in cattle. However, there are many questions concerning the exact functional and/or temporal relationships between these individual processes which finally result in the expulsion of the calf and the timely release of the placenta. Thus, parturition was induced in 270-day pregnant cows using the progesterone receptor blocker aglepristone (group AG, n=3), the prostaglandin F-2 alpha analog cloprostenol (group PG, n=4), and the glucocorticoid dexamethasone (group GC, n=4) to characterize the effect on maternal steroid and prostaglandin levels and to identify immediate subsequent changes in placental morphology and gene expression as compared with untreated controls sampled on day 272 (group D272, n=3) and cows during normal parturition (group NT, n=4). All calves of the treatment groups were born on days 271-272, whereas gestational length in NT cows was 280.5 +/- 1.3 days. However, none of the treatments significantly induced the prepartal remodeling of placentomes characterized by a decline in trophoblast giant cells and reduction of the caruncular epithelium. Data on placental CYP17 and COX2 expression confirm that these key enzymes are upregulated by GC, whereas placental aromatase expression was not affected by any treatment. Maternal progesterone and prostaglandin profiles suggest differential effects of the treatments on luteal function and placental or uterine prostaglandin production. The results provide new information on the initiation of parturition in cattle but raise many new questions.Item Placental steroids in cattle: Hormones, placental growth factors or by-products of trophoblast giant cell differentiation?(Johann Ambrosius Barth Verlag Medizinverlage Heidelberg, 2008-07) Schuler, Gerhard; Greven, Helga; Kowalewski, Mariusz Pawel; Hoffmann, Bernd; Doering, Barbara; Özalp, Gözde Rabia; Uludağ Üniversites/Veteriner Fakültesi/Kadın Hastalıkları ve Doğum Anabilim Dalı.; 0000-0003-4694-6937; AAE-3607-2019; 8555276100The bovine placenta produces large amounts of steroids, mainly estrone (E1) and progesterone (P-4). Specific features of bovine placental steroidogenesis are I) the expression of all enzymes needed for the production of estrogens from cholesterol in the trophoblast 2) an only marginal and temporal contribution to peripheral maternal P4 levels restricted to a period between approx. days 150-240 of gestation 3) the predominance of sulfoconjugated over free El and 4) a complementary setting of steroidogenic enzymes in the two morphologically discriminable trophoblast cell types, the uninucleated trophoblast cells (UTC) and the trophoblast giant cells (TGC). In cattle so far no definite information is available on the specific biological roles of placental estrogens and P4. However, the detection of estrogen receptors and progesterone receptors in the placentomes Suggests a role primarily as local regulators of caruncular growth, differentiation and functions. Inconsistent with a function as a caruncular growth factor is the strong evidence that in cattle placental estrogens enter the maternal compartment almost completely as estrone Sulfate (EIS), which is not active at classical nuclear receptors. Oil the other hand, E IS may be converted locally to free active estrogens via the action of steroid sulfatase (StS), which has been detected in specific parts of the bovine carancular epithelium. Alternatively or in addition, StS expression in the caruncular epithelium may serve the utilization of sulfated neutral steroid precursors (e.g. pregrienolone sulfate or cholesterol sulfate) supplied with maternal blood, thus providing free substrates for further metabolization in the adjacent trophoblast. The down-regulation of P450scc and P450c17 and the Up-regulation of 3B-HSD and aromatase during the differentiation of TGC from UTC in parallel with the up-regulation of ERE and estrogen sulfotransferase in maturing TGC suggests a function of placental estrogens primarily as auto-or intracrine regulators during this process and assigns to conjugated placental estrogens a role as inactivated by-products of TGC differentiation intended for excretion. Collectively, despite some evidence from recent studies for putative roles of placental steroids in cattle their exact functions in the bovine species remain still undefined.Item Use of the progesterone (P4) receptor antagonist aglepristone to characterize the role of P4 withdrawal for parturition and placental release in cows(Bioscientifica, 2010-10) Shenavai, Sima; Hoffmann, Bernd; Dilly, Marc; Pfarrer, Christiane D.; Schüler, Gerhard; Özalp, Gözde Rabia; Çalışkan, Çağlar; Seyrek İntaş, Kamil; Uludağ Üniversitesi/Veterinerlik Fakültesi/Doğum ve Jinekoloji Bölümü.; 0000-0003-4694-6937; AAH-7292-2019; AAE-3607-2019; 23985710500; 23984353800; 6603409870In late pregnant cows, progesterone (P-4) is mainly of luteal origin. However, the trophoblast may provide high local P-4 concentrations in the uterus. To test for the importance of a complete P-4 withdrawal for parturition-related processes and placental release, the P-4 receptor (PGR) blocker aglepristone (Ap) was administered to three cows on days 270 and 271 of pregnancy. A complete opening of the cervix was observed 46.5 +/- 7.3 h after the start of treatment. However, expulsion of the calves was impaired obviously because of insufficient myometrial activity, and placental membranes were retained for at least 10 days. Measurement of P-4 concentrations indicated that PGR blockage induced luteolysis. To investigate the role of P-4 withdrawal for the prepartal tissue remodeling of the placentomes, the caruncular epithelium was evaluated by morphometry, and the percentage of trophoblast giant cells (TGCs) relative to the total number of trophoblast cells were assessed. Caruncular epithelium in Ap-treated cows (D272 + Ap) was immature (30.5 +/- 3.3%) and not different from untreated controls (elected cesarean section (CS) on day 272; D272-CS; 31.5 +/- 1.4%), whereas it was significantly reduced at normal term (D280.5 +/- 1.3; 21.0 +/- 6.1%; P=0.011). Correspondingly, the percentage of TGCs were 20.1 +/- 1.4 in D272 + Ap, 22.1 +/- 4.8 in D272-CS, and 9.8 +/- 3.9 at term (P=0.001). No effect was detected on placental estrogen synthesis. The results showed that in late pregnant cows, P-4 withdrawal only induces a limited spectrum of the processes related to normal parturition and is not a crucial factor for the prepartal tissue remodeling in placentomes and the timely release of the placenta.