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Biomedical subjects

D Schams

Publications and source records attributed to D Schams.

At least 73 records · Page 4Linked to original sources
PubMed1997

Egg-cumulus-oviduct interactions and fertilization.

In this communication we approach the events leading to fertilization in mammals by examining the triangle of egg, sperm and oviductal cell taking account of the local physiology and focussing on auto/paracrine interactions. The expression of growth factors and extra-cellular matrix (ECM)-components in bovine ovarian granulosa- and theca-cells, the oocyte-cumulus complex (OOC) and oviductal epithelium, as well as some of the corresponding secreted proteins can be detected through the estrous cycle. Components of the insulin-like (IGF), fibroblast (FGF) and transforming (TGF) growth factor systems, and also metalloproteinase 1 (MMP1) and urokinase (uPA) are found to be modulated in these cells prior to fertilization. Different expression levels between the cell types are found, each representative of a specific reaction window within that particular stage of the cycle. Our findings support the concept that most of the observed tissue in the reproductive tract is dependent upon on the effects of gonadotropins or steroids, but that the fine-regulation is conveyed by, for example, growth factors and ECM-components. We suggest a sophisticated, auto/paracrine and species-specific crosstalk of growth factors and ECM components between the different cell types involved, enabling fertilization and development of the embryo at the right time and in the right location.

Animals↗
PubMed1997

Seasonal levels of reproductive hormones and their relationship to the antler cycle of male and female reindeer (Rangifer tarandus).

Seasonal levels of LH, FSH, testosterone (T), estradiol, progesterone (P), and prolactin (PRL) were determined in the plasma of five adult bulls, and five barren and four pregnant cows of Alaskan reindeer (Rangifer tarandus), which were sampled every 3 weeks for 54 weeks. The male reproductive axis was sequentially activated; LH peaked in May-June (2 ng/ml), FSH in June (51 ng/ml), and T in September (11.8 ng/ml). LH levels in females reached a maximum in both groups at the end of August (the beginning of the rut). Seasonal variation in FSH was minimal in pregnant cows, but exhibited one elevation (41 ng/ml) in barren ones in November. T levels in cows remained at barely detectable levels. The decrease of T values observed in both groups in December and March was not significant. PRL peaked in May in cows (135 ng/ml pregnant, 140 ng/ml non-pregnant) and in June in bulls (92 ng/ml). Estradiol was highest in bulls in the rut (August), in non-pregnant cows in January and in pregnant cows in April, shortly before parturition. P levels in the pregnant cows rose from September and peaked (9 ng/ml) shortly before parturition in April. In the non-pregnant females P values increased and decreased several times before peaking (5 ng/ml) in March. In the males, the variation of T and estradiol levels correlated relatively well with the antler cycle but in the females the variation of neither estradiol, progesterone nor T appeared to be related to mineralization or casting of antlers.

Animals↗
PubMed1997

Machine milking of Ostfriesian and Lacaune dairy sheep: udder anatomy, milk ejection and milking characteristics.

Mammary cistern anatomy derived from ultrasound measurement, milk ejection in response to exogenous oxytocin and oxytocin release and milking characteristics with and without manual prestimulation in early (months 2-4) and late (months 5-8) lactation were investigated in Lacaune and Ostfriesian dairy ewes. Vertical ultrasound cisternal cross sections of the cisternal cavities did not differ in the two breeds, whereas the cisternal area fraction located lower than the exit into the teat channel was larger in Ostfriesian than in Lacaune sheep. The cisternal area enlarged within 1 min in response to i.v. oxytocin injection, indicating milk ejection. During milking, oxytocin concentrations in Lacaune generally increased dramatically within 0.5 min from the start of prestimulation or milking, whereas only slight or no oxytocin release was detected during milking without prestimulation in Ostfriesian ewes. Prestimulation induced oxytocin release in Ostfriesian sheep within 1-2 min after the start of milking, indicating delayed response to stimulation. Two peaked milk flow curves were observed when oxytocin release and milk ejection occurred only after removal of cisternal milk. This type of milk flow was more frequent in Ostfriesian than in Lacaune ewes and was reduced in both breeds by prestimulation, while the frequency of one peaked milk flow curves increased. During the course of lactation, milk yield, main milk fraction and milk flow rates decreased, while stripping yield was almost unchanged. Although milk yield was similar in both breeds, milk flow was lower and stripping yield was higher in Ostfriesian than in Lacaune ewes. We conclude that milk ejection in ewes occurred in response to elevated oxytocin concentrations. In Ostfriesian ewes reduced and delayed oxytocin response to teat stimulation resulted in milk ejection only during stripping. Therefore, and probably because a larger volume of the cistern was located below the teat exit in the Ostfriesian breed, stripping yield was higher in Ostfriesian than in Lacaune sheep.

Animals↗
PubMed1997

Detection of mRNA and immunoreactive proteins for acidic and basic fibroblast growth factor and expression of the fibroblast growth factor receptors in the bovine oviduct.

The heparin-binding acidic and basic fibroblast growth factors (aFGF, bFGF) and their receptors in the bovine oviduct are described. By means of western blot analysis one 18 kDa aFGF and two bFGF proteins (16 and 18 kDa, respectively) were detected in oviductal flushings. Different concentrations of these two growth factors could be measured in oviductal flushings during the oestrous cycle: concentrations of aFGF protein were significantly higher at ovulation (mean +/- SEM; 5.3 +/- 0.5 ng ml-1) than during the luteal phase (3.0 +/- 0.3 ng ml-1); concentrations of bFGF were higher at the preovulatory stage (3.5 +/- 0.7 ng ml-1) than at the post-ovulatory stage (1.3 +/- 0.15 ng ml-1). Immunohistochemical studies using a/bFGF-specific antibodies indicated that these growth factors were localized mainly in oviduct epithelial cells. The sequence of the bovine FGF receptor (FGFR) was partly determined. Quantification of mRNAs by an RNase-protection assay (RPA) showed that expression of aFGF and bFGF was different during the oestrous cycle, indicating that the regulation of aFGF is separate from that of bFGF. Only mRNA encoding bFGF and FGFR could be detected in cumulus-oocyte complexes by reverse transcription PCR. In summary, the components of the FGF system were found in the bovine oviduct suggesting an autocrine or paracrine regulation involving oviduct cells and cumulus-oocyte complexes.

Animals↗
PubMed1997

Prostaglandin F2 alpha promotes the inhibitory action of endothelin-1 on the bovine luteal function in vitro.

Prostaglandin F2 alpha (PGF2 alpha) is a primary luteolysin in the cow. Although the mechanisms involved in luteolysis are thought to be a complex of its direct action on luteal cells and indirect effect on luteal blood flow, the detailed mechanisms remain to be elucidated. This study focuses on the possible interaction of endothelial cells-derived endothelin-1 (ET-1) with PGF2 alpha in the rapid suppression of progesterone release from the bovine corpus luteum (CL). In in vitro microdialysis system (MDS) of CL, PGF2 alpha acutely stimulated the release of progesterone and oxytocin during infusion and ET-1 release after infusion. Moreover, PGF2 alpha induced slight decrease of progesterone release during the last period of the experiment (8-11 h after PGF2 alpha exposure). Two 1 h-perfusions of ET-1 at 3 h intervals induced only a slight decrease of progesterone release after the second perfusion. This treatment also affected the oxytocin release; the first ET-1 perfusion produced an acute stimulation, whereas the second ET-1 perfusion inhibited the release to below 50%. When the CL pieces were pre-perfused with PGF2 alpha for 2 h, the two consecutive perfusion of ET-1 at 3 h intervals induced drastic decrease in progesterone and oxytocin release only after the second ET-1 perfusion. Thus, a pre-exposure with PGF2 alpha clearly potentiated the inhibiting activity of ET-1 in the progesterone release. These results suggest a physiological impact of PGF2 alpha and ET-1 in the rapid cascade of functional luteolysis in vivo, and a possible interaction between endothelial cells and luteal cells.

Animals↗
PubMed1997

Expression of transforming growth factors alpha and beta-1 messenger RNA in the bovine mammary gland during different stages of development and lactation.

It is now widely accepted that the mammary gland is under interconnected hormonal and local control. Growth factors are involved in the intercellular signalling of the gland. Our aim was the detection of transforming growth factors alpha (TGF-alpha) and beta 1 (TGF-beta 1) messenger RNA during mammogenesis, lactogenesis, galactopoiesis and involution in the bovine mammary gland (total n = 27). During these stages the RNA was assessed by means of ribonuclease protection assay and reverse transcription-polymerase chain reaction (RT-PCR). To study possible influences of oestrogen, progesterone and prolactin on growth factor expression, mammary RNA was obtained from heifers after induced mammogenesis and lactogenesis, with and without additional prolactin inhibition (total n = 20). Very low levels of TGF-alpha and TGF-beta 1 expression were detected during lactogenesis and galactopoiesis, increasing levels during mammogenesis of primigravid heifers, and highest levels during mammogenesis of virgin heifers and during involution. TGF-alpha expression after induced mammogenesis was greater than after induced lactogenesis or physiological mammogenesis during pregnancy. Furthermore, TGF-alpha mRNA contents increased after prolactin inhibition. TGF-beta 1 expression was almost equal after induced mammogenesis and lactogenesis, but greater than during the physiological mammogenesis and lactogenesis. In conclusion, it can be assumed that growth promoting TGF-alpha and growth inhibiting TGF-beta 1 are co-expressed in the bovine mammary gland. Higher mRNA contents of both factors during mammogenesis and involution may indicate autocrine or paracrine functions for these growth factors during proliferation and reorganisation of the mammary tissue.

Animals↗
PubMed1997

Response of catecholamines to manual teat stimulation or machine-milking of Lacaune and Friesen dairy ewes.

Increased sympathetic activity, including peripheral release of catecholamines, has been hypothesized to inhibit the milk ejection reflex by blocking the release of oxytocin, by blocking the effect of oxytocin at the mammary gland, or both. We attempted to relate differences in milking characteristics of Lacaune and East Friesen ewes to the degree of sympathetic arousal, responses of catecholamines and oxytocin to machine-milking and to manual teat stimulation followed by milking. Peripheral concentrations of epinephrine, 67 +/- 6 pg/ml for Lacaunes and 57 +/- 5 pg/ml for Friesens, were essentially constant. Peripheral concentrations of norepinephrine averaged 682 +/- 68 pg/ml for Lacaunes and 250 +/- 54 pg/ml for Friesens. Elevated norepinephrine concentrations during the pretreatment period were associated with the inhibition of oxytocin responses. When norepinephrine concentrations during the pretreatment period exceeded 300 pg/ml for Friescens, or were rising and exceeded 700 pg/ml at initiation of the experimental period for Lacaunes, oxytocin release was inhibited. Results from this study clearly showed that basal concentrations of norepinephrine vary with breed of ewes and provided the first direct evidence that increased sympathetic activity can result in central inhibition of the milk ejection reflex.

Animals↗
PubMed1996

Effects of local growth factors on the secretory function of bovine corpus luteum during the oestrous cycle and pregnancy in vitro.

The impact of insulin-like growth factor-I (IGF-I) basic fibroblast growth factor (bFGF), endothelin-1 (ET-1), tumour necrosis factor-alpha (TNF-alpha), transforming growth factor-alpha (TGF-alpha) and platelet-derived growth factor (PDGF) on the release of progesterone (P4) and oxytocin (OT) from individual bovine corpora lutea at different stages of the oestrous cycle and pregnancy was evaluated with a microdialysis system (MDS) in vitro. IGF-I (1 microgram mL-1) induced significantly the acute effects on P4 release at the late luteal stage (Days 15-18) and early pregnancy (Days 60-120), whereas bFGF (100 ng mL-1) was extremely effective in stimulating P4 release particularly during the mid-luteal stage (Days 8-12). Both peptides stimulated (P < 0.05) the release of OT throughout the three luteal stages and during early and late pregnancy (Days 30-60 and Days 150-210). ET-1 (100 ng mL-1) clearly inhibited P4 release during the early (Days 5-7) and mid-luteal phase and stimulated OT release only during the mid-luteal stage (P < 0.001). TNF-alpha (100 ng mL-1) stimulated the release of P4 exclusively at the early luteal phase (P < 0.05), whereas OT secretion was increased by TNF-alpha during all stages of the oestrous cycle (P < 0.001). TGF-alpha and PDGF (100 ng mL-1) were effective in stimulating P4 release particularly during late pregnancy (P < 0.05). In contrast, stimulation of OT secretion by TGF-alpha was maximal during the late-luteal stage (P < 0.001), whereas PDGF significantly increased OT secretion during the oestrous cycle (except the early luteal stage) and pregnancy (P < 0.001). The data demonstrate distinct and stage-specific effects of growth factors on P4 and OT secretion in vitro. IGF-I, bFGF and TGF-alpha may play an important role in corpus luteum (CL) function during the oestrous cycle and pregnancy since they are locally expressed and synthesized, there are receptors for these growth factors, and they have been demonstrated to exert biological effects on the CL.

Animals↗
PubMed1996

Depression of the somatotropic cells in the bovine pituitary gland due to application of recombinant bovine somatotropin--an immunohistochemical and morphometric study.

The morphological alterations in the bovine pituitary gland resulting from the administration of recombinant bovine somatotropin (rBST) are described. Three groups of German Simmental heifers (12 animals for each group) were treated. Group 1 received a placebo (vehicle), group 2320 mg and group 3640 mg of a prolonged-release formulation of rBST at 2 week intervals. Treatments were started with an average body weight of 286 +/- 2.5 kg and continued until one week before the animals were slaughtered with an average body weight of 520 +/- 3.2 kg. Double immunohistochemical labelling using rabbit anti-prolactin (PRL) and chicken anti-BST antibodies was performed on paraffin serial sections of the pituitary glands. Morphometric analyses revealed a dose-dependent decrease of the volume fraction of the somatotropic cells due to a reduction in number and a diminution of the mean cellular volume. No significant differences in the volume fraction of the mammotropic cells were seen. The recorded reduction of the somatotropic cells is thought to be the result of a negative feedback upon the secretory activity as a result of long-term rBST treatment.

Animals↗
PubMed1995

Effects of prostaglandins and oestradiol-17 beta on oxytocin binding in cultured bovine luteal cells.

The aim of the investigation was to evaluate the possible action of prostaglandins (PGs) and oestradiol-17 beta (oestradiol) on the specific binding for oxytocin in bovine luteal cells. Cultured cells of bovine corpora lutea at the mid-luteal stage (Day 8-12 of the oestrous cycle) were examined for the presence of oxytocin receptors by a radioreceptor assay using the 125I-labelled oxytocin antagonist [d(CH2)5,Tyr(Me)2,Thr4,Tyr-NH29]-vasotocin (125I-OVT) as a ligand. The cells were cultured for 48 h in total. In the final 15 h of culture, the luteal cells were exposed to varying concentrations of PGF2 alpha, PGE2 and/or oestradiol. After culture, the cells were incubated with 37,000 dpm (0.5 nM) 125I-OVT with or without 100 nM of unlabelled oxytocin. PGF2 alpha, at 10(-8) M and 10(-7) M, stimulated the specific binding for oxytocin to levels as high as 128% of controls (P < 0.01); by contrast, PGE2, PGI2 or oestradiol had no effect on oxytocin binding. Scatchard analysis revealed that the concentration of oxytocin receptors was increased (P < 0.05) from 6.7 fmol micrograms-1 DNA to 8.4 fmol micrograms-1 DNA by stimulation with 10(-7) M of PGF2 alpha without changing the binding affinity. No further increase in the specific binding was observed when PGF2 alpha was used in combination with PGE2, PGI2 or oestradiol at a concentration of 10(-7) M. Addition of indomethacin (28 microM) resulted in the inhibition of PGF2 alpha secretion, coinciding with a significant decrease in oxytocin binding (P < 0.01). However, addition of arachidonic acid (100 microM) caused a significant increase in the secretion of PGF2 alpha and the specific binding for oxytocin concomitantly (P < 0.05). When the protein kinase C (PKC) activity of the luteal cells was inactivated by preincubating cells for 13 h with 1 microM phorbol 12-myristate 13-acetate before PGF2 alpha stimulation, the specific binding for oxytocin was not affected by PGF2 alpha stimulation (10(-7) M) in the final 15 h of culture. These data suggest that PGF2 alpha may be one of the potent regulators for luteal oxytocin receptors in a paracrine and/or autocrine manner, and that its action is mediated by PKC.

Animals↗
PubMed1994

Effect of recombinant bovine somatotropin (rBST) on follicular IGF-I contents and the ovarian response following superovulatory treatment in dairy cows: a preliminary study.

Somatotropin and FSH act synergystically on insulin-like growth factor-I (IGF-I) synthesis in ovarian follicles; IGF-I regulates several granulosa cell specific functions and may thereby be beneficial in bovine superovulation. In a series of 3 experiments we investigated the effects of recombinant bovine somatotropin (rBST) on several parameters of the superovulatory response in dairy cows. A total of 81 Holstein Friesian crossbred dairy cows received either 640 mg rBST or the vehicle (controls) on Day 4 or 13 of the superovulation schedule. Superovulation was induced with 2500 IU PMSG on Day 9. The cows were artificially inseminated on Day 13. In Experiment 1, on Days 4, 8, 11, 13 and 17 4 to 5 animals each were slaughtered to obtain follicular fluid, endometrium and plasma. The rBST application increased IGF-I contents in plasma and follicular fluid on Days 8, 11 and 13 (P<0.05) in the treated cows when compared with that of the controls. Plasma and follicular IGF-I contents were correlated closely (rBST: r=0.90, n=10; control: r=0.94, n=9). The number of antral follicles increased following rBST treatment, and on the day of artificial insemination (AI) twice as many follicles>4 mm were counted in the rBST treated animals than in the control group. In Experiment 2, the flushing of 38 donors on Day 7 after AI resulted in more transferable embryos in the rBST group than in the control group (4.2+/-1.0 vs 2.5+/-0.7; P<0.05). In contrast, in Experiment 3 involving 21 animals when rBST was administered at the time of AI the superovulation response was not altered. It is concluded that rBST increases follicular and plasma IGF-I contents and thereby has profound effects on follicular and early embryonic development.

Journal Article↗
PubMed1994

Machine milking of dairy goats during lactation: udder anatomy, milking characteristics, and blood concentrations of oxytocin and prolactin.

Forty-four goats were milked and milk flow recorded without or with 1 min manual prestimulation in early, mid and late lactation. Ultrasound measurements of cross sections of the whole mammary gland were performed in a water bath. In additional experiments with 15 goats, milk flow was recorded and frequent blood samples were taken for the determination of oxytocin and prolactin concentrations. Milk yield increased from the first to the third lactation and decreased markedly during the course of lactation. Average and peak milk flow rates were closely related to the actual milk yield. The ultrasound cisternal area was 27.4 +/- 1.5% of the entire udder half cross section. Milking characteristics were scarcely different without or with prestimulation, although oxytocin was released within 30 s after the start of prestimulation, whereas oxytocin concentrations without prestimulation increased only after the start of milking. Concentrations of prolactin were higher during July and August than in April, and increased similarly with or without prestimulation during milking. In contrast to dairy cows, prestimulation and an opportune release of oxytocin during milking does not significantly influence the course of milk flow in goats, and this is probably because large amounts of cisternal milk allow milk ejection to be induced only after the start of milking without causing bimodal or otherwise reduced milk flow.

Animals↗
PubMed1994

Continuously elevated concentrations of oxytocin during milking are necessary for complete milk removal in dairy cows.

The importance of elevated concentrations of oxytocin (OT) during the entire milking period was investigated in seven primiparous dairy cows with inherent disturbed milk ejection and in sixteen healthy cows with disturbed milk ejection induced by placing them in an operating theatre. Disturbance of milk removal in both groups has previously been demonstrated to be exclusively due to central blockage of the expected OT release in response to teat stimulation and milking. However, milk ejection can be induced by exogenous OT. OT (0.2 i.u.) was injected i.v. before milking and 49 +/- 6% of the total milk was removed. When plasma OT decreased, milk flow stopped. In response to a second and third injection of 0.2 i.u. OT, 30 +/- 4 and 7 +/- 2% of the milk were removed respectively. The remaining milk was removed with 10 i.u. OT. The lag time from injection of OT to the start of milk flow was inversely correlated with the amount of milk actually removed in response to the OT injection. If 0.2 i.u. OT was injected during intramammary pressure (IMP) recording, IMP immediately increased to its maximum value. After 2.5 +/- 0.3 min, IMP decreased to an intermediate IMP (between preinjection and maximum IMP). After two additional injections of 0.2 i.u. OT and after injection of 0.5 i.u. OT, IMP increased to a similar maximum. However, after injection of 0.5 i.u. OT, maximum IMP lasted longer (2.9 +/- 0.3 min; P < 0.05) than after injections of 0.2 i.u. If OT was continuously infused (0.15 i.u./min) during milking, milk flow lasted until the udder was completely emptied. IMP increased during OT infusion to a maximum which remained stable until infusion was stopped after 10 min. The same IMP maximum was reached after the first individual OT injection (0.2 i.u.), but when plasma OT decreased towards basal concentrations, milk flow ceased and IMP decreased to an intermediate level. Thus continuously elevated OT concentrations such as those during infusion or during normal milking are necessary for complete milk removal.

Animals↗
PubMed1994

Expression of insulin-like growth factor 1 (IGF-1) in the bovine oviduct during the oestrous cycle.

Growth factors are known to take part in the regulation of reproduction. Here we present evidence for the expression of insulin-like growth factor 1 (IGF-1) in the bovine oviduct. Two IGF-1 specific mRNA-transcripts of 1.5 and 4.4 kb were detected during the whole oestrous cycle, and showed increased expression after ovulation. Complete homology to the known IGF-1 sequence was achieved by specific RT-PCR (reverse transcription-polymerase chain reaction) amplification followed by dideoxysequencing of this 210 bp fragment. IGF-1 protein was localized in the secretory cells of the oviduct epithelium using immunohistochemical techniques. We suggest possible effects of IGF-1 during ovulation either on the oviductal cells or on the early embryo.

Animals↗
PubMed1994

Secretory pattern of metabolic hormones in the lactating sow.

Two experiments were conducted to monitor hormonal changes during lactation in crossbred sows (Pietrain x German Landrace). Sows were fed twice daily without weighing the remaining food. Number of piglets was not standardized. Plasma concentrations of growth hormone (GH), prolactin (PRL), insulin-like growth factor-1 (IGF-1), IGF-2, insulin (INS), triiodothyronine (T3), thyroxin (T4), free thyroxin (FT4), non esterified fatty acids (NEFA) and glucose (GLUC) were determined by RIA, EIA or enzymatically. In exp. A (n = 5 sows), blood samples were taken via permanent jugular cannula in weekly 24 h windows at 20 min intervals and additionally once daily for 6 weeks during lactation and for 3 days after weaning. In exp. B (n = 24 sows), blood was collected by needle puncture of the ear vein 2 and 1 week before parturition, the 1st and 3rd-4th week of lactation and 1 and 2 weeks after weaning. GH (0.8 ng/ml) and PRL (10.2 ng/ml) increased with onset of lactation (3.3 resp. 91.5 ng/ml), remained at high levels (2.5-2.8 resp. 39-41 ng/ml) during the 2nd and 3rd week, declined slowly thereafter and considerably after weaning to concentrations of 0.7 resp. 2.7 ng/ml. During lactation in 4 of 5 sows in exp. A, the typical episodic secretory pattern of GH and PRL was lost due to frequent suckling. Basal values, as known from non lactating sows, were not reached and number of pulses was elevated during lactation for both pituitary hormones. Insulin levels showed a high individual variation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Identification of antigenic differences of recombinant and pituitary bovine growth hormone using monoclonal antibodies.

For characterization and determination of recombinant bovine GH (rbGH) eight monoclonal antibodies (MAb) were produced against rbGH from Monsanto. The various MAb showed different affinities to rbGH, pituitary bovine GH (pbGH), and pituitary ovine GH (poGH). With epitope analysis several MAb were shown to recognize different epitopes of rbGH. The MAb MUC-rbGH-3A11 and MUC-rbGH-1E5 were used to develop a Sandwich ELISA. By checking the specificity of the assay no cross reactivity was found with pituitary porcine GH, pituitary human GH, bovine or ovine prolactin and little cross reactivity with poGH could be found. The Sandwich ELISA detected various rbGH (Monsanto, Elanco, Cyanamid) with different N-terminal amino acids and discriminated between rbGH and pituitary bovine GH by an affinity factor of 2.0. The detection level was 2 ng rbGH per ml PBS buffer. The recovery was about 86% in bovine serum. It might therefore be possible to detect rbGH-treated cows using a Sandwich ELISA, but this would need a field study.

Animals↗