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Biomedical subjects

D Schams

Publications and source records attributed to D Schams.

At least 127 records · Page 7Linked to original sources
PubMed1989

Sequences of pituitary, ovarian and uterine hormone secretion during the first 5 weeks of pregnancy in dairy cattle.

Blood samples were collected frequently from permanent catheters placed in the aorta and caudal vena cava of 36 heifers in order to monitor the release pattern of LH, FSH, progesterone, oestradiol-17 beta, oxytocin, PGF-2 alpha, PGE-2 and PGI-2 (determined as its 6-keto-PGF-1 alpha metabolite). The frequency of secretory bursts of both gonadotrophins and progesterone was similar in early pregnant and cyclic animals, whereas the amplitude of LH and progesterone increased between 2 and 4 weeks of gestation. Concentrations of circulating oestradiol-17 beta and oxytocin were already lower at Days 4-7 in pregnant than in cyclic animals. Oestradiol-17 beta originated after Day 14 from the uterus rather than the ovary. A sustained release of oxytocin most probably from the posterior pituitary gland and a concomitant decrease of progesterone occurred in about two-thirds of pregnant animals during Days 19-23. Insemination could induce releases of PGF-2 alpha lasting up to 2 h. In addition, basal concentrations of PGF-2 alpha during the first 6 days after oestrus were approximately 2-fold higher in inseminated than in non-inseminated cyclic heifers. A parallel increase of PGF-2 alpha and PGI-2 occurred between Days 30 and 33 of gestation. Early embryonic mortality resulted, at least up to Day 35, in 4-7 concomitant secretory bursts of PGF-2 alpha and luteal oxytocin. There was a delay of 20-26 h between the first and second release. The present results from in-vivo experiments point towards major endocrine changes in cattle within a few days after conception, resulting in an early inhibition of follicular oestradiol-17 beta and luteal oxytocin facilitating the suppression of luteolytic releases of PGF-2 alpha.

Animals↗
PubMed1989

Ovarian peptides in the cow and sheep.

There are indications that ovarian oxytocin is involved in luteolysis and the endometrium may play a key role for the events of luteolysis. A certain priming period with progesterone is a prerequisite for the induction of luteolysis. Treatment of heifers with progesterone for 4 days beginning after the LH surge shortens the oestrous cycle length significantly. Besides an involvement in luteolysis, there are indications for an intraovarian function of oxytocin influencing steroidogenesis by inhibition of progesterone secretion. Growth factors have been identified in ovarian tissue and insulin-like growth factor-I has a very potent effect on bovine granulosa cell function. Growth factors may be involved in the growth and differentiation of follicles.

Animals↗
PubMed1988

Dynamics of oxytocin, estrogen and progestin receptors in the bovine endometrium during the estrous cycle.

The levels of oxytocin receptor (OTR), cytosolic progestin receptor (cPR), cytosolic and nuclear estrogen receptor (cER, nER) were measured in the endometrium of 28 heifers that had been slaughtered on a defined day of the estrous cycle. In an additional, trial endometrial tissue obtained from 78 heifers or cows at the abattoir was analysed for OTR. OTR was absent during the luteal phase (after day 6), but a minor elevation was observed after day 15. OTR increased rapidly after luteolysis on days 17-18 reaching a maximum during estrous on day 21, and decreased again during days 1-6. cER and cPR were different to OTR but followed a similar pattern with maximal levels during days 1-8 of the estrous cycle. At day 12 both receptors were minimal and increased again towards day 21. nER was maximal at day 19-21 coinciding with maximal estradiol levels and estrous. Our data indicate that owing to an increasing sensitivity of the endometrium to progesterone and estradiol after day 12, these steroids may be mainly responsible for the initiation of first PGF2 alpha surges and luteolysis. Oxytocin seems to be of minor importance at this stage owing to low sensitivity of the endometrium for oxytocin.

Animals↗
PubMed1988

Effect of continuous infusion of oxytocin on length of the oestrous cycle and luteolysis in cattle.

In Exp. I oxytocin (60 micrograms/100 kg/day) was infused into the jugular vein of 3 heifers on Days 14-22, 15-18 and 16-19 of the oestrous cycle respectively. In Exp. II 5 heifers were infused with 12 micrograms oxytocin/100 kg/day from Day 15 of the oestrous cycle until clear signs of oestrus. Blood samples were taken from the contralateral jugular vein at 2-h intervals from the start of the infusion. The oestrous cycle before and after treatment served as the controls for each animal. Blood samples were taken less frequently during the control cycles. In Exp. III 3 heifers were infused with 12 micrograms oxytocin/100 kg/day for 50 h before expected oestrus and slaughtered 30-40 min after the end of infusion for determination of oxytocin receptor amounts in the endometrium. Three other heifers slaughtered at the same days of the cycle served as controls. Peripheral concentrations of oxytocin during infusion ranged between 155 and 641 pg/ml in Exp. I and 18 and 25 pg/ml in Exp. II. In 4 our of 8 heifers of Exps I and II, one high pulse of 15-keto-13,14-dihydro-prostaglandin F-2 alpha (PGFM) appeared soon after the start of oxytocin infusion followed by some irregular pulses. The first PGFM pulse was accompanied by a transient (10-14 h) decrease of blood progesterone concentration. High regular pulses of PGFM in all heifers examined were measured between Days 17 and 19 during spontaneous luteolysis. No change in length of the oestrous cycle or secretion patterns of progesterone, PGFM and LH was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Insulin-like growth factor-I stimulates oxytocin and progesterone production by bovine granulosa cells in culture.

The effect of insulin-like growth factor-I (IGF-I), epidermal growth factor (EGF), fibroblast growth factor (FGF) and nerve growth factor (NGF) on production of oxytocin and progesterone by cultured bovine granulosa and luteal cells was studied. Secretion of oxytocin was stimulated, in a dose-dependent manner, by IGF-I at 48 and 120 h of culture to levels much higher than those after stimulation with LH, FSH, EGF, FGF or NGF. A similar effect of IGF-I was observed for progesterone but, in contrast to oxytocin, secretion of progesterone was not increased by EGF, NGF or FGF. During primary culture, for 4 h, of dispersed bovine luteal cells obtained from corpora lutea between days 4 and 10 of the oestrous cycle, all the growth factors tested failed to stimulate secretion of oxytocin or progesterone. The data suggest the relevance of growth factors (especially IGF-I) for ovarian physiology and their possible importance for differentiation of follicles and luteinization.

Animals↗
PubMed1988

Characteristics of milk ejection, associated intramammary pressure changes and oxytocin release in the mare.

The neuroendocrine reflex theory of milk ejection was investigated in the horse under natural suckling conditions. To this end 12 lactating mares were provided with acute jugular catheters and with intramammary pressure (IMP) recording catheters. The foal had free access to the contralateral mammary complex. Intramammary pressure could thus be recorded while blood was drawn simultaneously for oxytocin analysis from the undisturbed animal. Suckling periods associated with a characteristic increase in IMP lasted significantly longer than unsuccessful nursing attempts. Elements of successful sucklings involved physical stimulation of the mammary gland, a quiet phase and a sudden increase in IMP. Successful suckling took place at about 20-min intervals with a wide range from less than 5 min to greater than 100 min. Between 5 and 10 mU oxytocin i.v. were sufficient to evoke an increase in IMP identical in shape and duration to a naturally induced increase in IMP. Mean peak oxytocin levels reached 15.8 pmol/l plasma, with a maximal release of 39 pmol/l. In the majority of cases (greater than 80%) peak oxytocin release did not occur until after the increase in IMP; in some cases an oxytocin surge was not detectable at all, despite a milk ejection-associated increase in IMP. In three cases increase in IMP could be observed while the foals were away from the mother with no signs of any intention to suckle. The data indicate that in the horse some elements of the neuroendocrine reflex, such as tactile stimulation of the teat and a surge of oxytocin before an increase in IMP, are facultative and not essential for normal milk ejection.

Animals↗
PubMed1988

Fetal and postnatal oxytocin secretion in the pig before and after a prostaglandin challenge.

Maturation of oxytocin secretion was studied in anaesthetized male and female 80 (n = 42) and 105 (n = 35) days-old fetal pigs and in conscious unrestrained piglets 4 weeks post partum (n = 11). Blood samples were taken from the maternal jugular vein and simultaneously from the exteriorized umbilical artery of fetuses (n = 4/sow) kept in utero under acute experimental conditions. Four weeks-old piglets were catheterized chronically. After initial observation of basal oxytocin secretion PGF2 alpha (0.5 mg in fetal and 2.5 mg in postnatal pigs as an intramuscular injection) was used as a challenge for oxytocin release. In sham groups physiological saline was injected. After treatment blood was collected up to 25 min (fetuses 80 days), 35 min (fetuses 105 days) or 125 min (piglets). Sampling interval was 5 min (fetuses 80 d) or 10 min (other groups). Maternal oxytocin concentrations remained at a stable level throughout the experiment and were not altered by PGF2 alpha application to the fetus. In the fetus, preinjection baseline oxytocin levels were obtained for all age groups with no sex difference. PGF2 alpha resulted in a rise (P less than 0.001) of fetal and postnatal oxytocin release within 5 min. In the day 80 fetal group only 60% of the animals responded with an increase of oxytocin concentration while 100% of the animals responded in all other age groups. Oxytocin levels remained elevated for the rest of the observation period in all age groups. Again, no sex difference was detected. The data demonstrate that oxytocin secretion is present and could be stimulated in the fetal pig as early as day 80 of fetal life. Maturational changes expressed by an increase in the number of fetuses responding to a challenge of PGF2 alpha with a release of oxytocin become apparent between day 80 and 105 of pregnancy.

Animals↗
PubMed1987

Expression of the oxytocin gene in the large cells of the bovine corpus luteum.

In the bovine ovary there is a delay of 4-6 days between the observed maximum of oxytocin mRNA and the peak in the luteal levels of oxytocin nonapeptide. This implies a maturation process involving components of the post-translational processing pathway. In situ hybridization shows the oxytocin gene to be transcribed exclusively in the large cells of the corpus luteum at the beginning of the estrous cycle.

Animals↗
PubMed1987

The effect of artificial photoperiodicity and antiandrogen treatment on the antler growth and plasma levels of LH, FSH, testosterone, prolactin and alkaline phosphatase in the male white-tailed deer.

1. Artificial extension of day-length in adult male white-tailed deer during the autumn induced: (a) premature casting of antlers, early onset of the new antler growth and out of season mineralization, (b) early elevation of plasma levels of prolactin, LH, FSH, testosterone and alkaline phosphatase and (c) out of season hair molt. 2. Intramuscular administration of the antiandrogen cyproterone acetate immediately after velvet shedding induced: (a) dramatic reduction of testosterone levels in plasma, (b) premature casting in bucks with fully mineralized antlers and (c) renewal of bone rebuilding activity in incompletely mineralized antlers which resulted in blockage of casting.

Alkaline Phosphatase↗
PubMed1987

Assessment of the sexual and antler potential of the male white-tailed deer (Odocoileus virginianus) by Gn-RH stimulation test.

Twelve mature white-tailed bucks were injected with gonadotropin regulating hormone (Gn-RH, 100 micrograms/deer) during the rut (November) and during the spring (April). In the rut, superior bucks (with actual or potential large body weight, trophy antlers and a high social rank) responded to Gn-RH with a small increase of LH (below 20 micrograms/ml) and a profound rise in testosterone (T) (30-50 ng/ml). The inferior animals exhibited high increase of LH (30-40 ng/ml) but a low rise in T (below 10 ng/ml). FSH levels increased only slightly after Gn-RH and the concentrations were not related to reproductive performance. During the spring, increase in LH levels after Gn-RH administration greatly exceeded the rise of T, but no relationship was found between hormonal levels and the reproductive potential. FSH levels increased remarkably after Gn-RH administration. Gn-RH (administered during the rut) might be used for assessment of the potential for reproductive and antler performance.

Animals↗
PubMed1987

The role of androstenedione and testosterone in the reproduction and antler growth of a male white-tailed deer.

Seasonal levels of androstenedione and testosterone were investigated in plasma of mature intact and castrated male white-tailed deer. In four intact bucks, androstenedione concentrations were low in February and March (around 1 nmol/l) and then increased significantly (P less than 0.05) from April to November (peak 2.34 nmol/l). Testosterone remained low (below 3.5 nmol/l) from February to August and then rose significantly (P less than 0.01) till November (peak 36.78 nmol/l). Both hormones declined from November to February. In three castrates, androstenedione levels remained virtually unchanged (averaging around 0.5 nmol/l) between January and September. After a rapid significant increase (P less than 0.05) till November (peak value 2.45 nmol/l), androstenedione concentrations declined quickly to a baseline level. Testosterone in castrates remained around 0.3 to 0.7 nmol/l for most of the year with a non-significant peak (1.45 nmol/l) in October. These data indicate that the spring and summer increase in androstenedione in the intact deer is of testicular origin; the fall peak, however, may be a result of increased production in the adrenal glands. It can be speculated that the increase in androstenedione in the blood of the male deer during the spring may be responsible for the seasonal initiation and support of antler growth as well as being supportive to the re-activation of the reproductive system.

Androstenedione↗
PubMed1987

Luteal peptides and intercellular communication.

The variety of peptides synthesized by the corpus luteum (relaxin, vasopressin, oxytocin and oxytocin-related neurophysin) and their possible intracellular effects are reviewed. After luteinization of the granulosa cells and in response to LH and FSH, the output of oxytocin is increased. In addition, insulin-like growth factor is a very potent stimulus of oxytocin secretion. Although luteal cells respond to gonadotrophins by increased production of progesterone, there is no further secretion of oxytocin. Oxytocin is localized in large luteal cells which seem not to be under the direct control of gonadotrophins. Synthesis of luteal oxytocin seems to occur during the early luteal phase according to measurements of oxytocin mRNA. Highest tissue concentrations and secretion under in-vitro conditions were observed during the mid-luteal phase, and so synthesis, storage and secretion are unlikely to occur concomitantly. Under in-vitro conditions, oxytocin is secreted concomitantly with neurophysin and progesterone, and there appears to be some form of communication between small and large luteal cells for the secretion of progesterone and oxytocin under in-vivo conditions. Evidence has been obtained that oxytocin may have local effects in the ovary by inhibition of secretion (synthesis ?) of progesterone, especially during the early luteal phase. A mechanism can be suggested whereby, under physiological conditions, oxytocin may delay the increase of progesterone by inhibition of progesterone secretion and therefore delay down regulation of its own receptor. This would prolong the life-span of the CL and the oestrous cycle. Exogenous progesterone given on Days 1-4 shortens the cycle to about 12 days. The best evidence that oxytocin may be involved in controlling luteolysis comes from immunization experiments in ewes and goats, but there is no clear evidence of this type for cattle. Basal concentrations of oxytocin at the end of the luteal phase may interact with oxytocin receptors after the inhibitory effect of progesterone in the uterus is reduced, thus initiating synthesis of PGF-2 alpha.

Animals↗
PubMed1986

Relationship of age to seasonal levels of LH, FSH, prolactin and testosterone in male, white-tailed deer.

Seasonal levels of LH, FSH, Prolactin (PRL) and testosterone (T) were determined in blood plasma of penned male white-tailed deer, ranging in age from 2 to 10 yr. Peak levels of T (observed around the rutting season in November) gradually increased until the 7th yr and then they began to decline slowly; a sharp decrease was registered in the 10th yr. Peak levels of PRL (measured in June) steadily increased until the 6th yr and then dropped rapidly in the 8-9-yr-old group. Peak concentrations of FSH (observed during September-October) rose gradually until the 6th yr, decreased in 8-yr-olds and then increased again in the 9th and 10th yr of life. On the other hand LH maxima (occurring during July-September) were rising until the 4th yr and then remained steady until the 6th yr. LH peaks in the 8th and 9th yr were more than 50% higher than that of the 4-6th yr. These data indicate that increasing peak levels coincide with approaching "prime male age" around 5-7 yr. In senior bucks (9-10 yr) decreasing gonadal function may be the sign of diminished responsiveness to pituitary hormones since gonadotrophins are elevated to the "castrate-type" levels.

Age Factors↗