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Biomedical subjects

D Schams

Publications and source records attributed to D Schams.

At least 145 records · Page 8Linked to original sources
PubMed1986

The effect of orally administered melatonin on the seasonality of deer pelage exchange, antler development, LH, FSH, prolactin, testosterone, T3, T4, cortisol and alkaline phosphatase.

Five milligrams of melatonin (M) per day was administered orally to four male white-tailed deer on a schedule that mimicked first decreasing and then increasing lengths of natural photoperiod. The following seasonal phenotypic and hormonal responses were observed: Pelage exchange, antler mineralization, velvet shedding, and rutting behavior of experimental animals were advanced by 50-55 days. Prolactin (PRL) levels exhibited a bimodal curve with peaks in May and August, as compared to a monomodal curve of controls (peak in June). Peak FSH levels of M-fed deer were advanced 2 months as compared to controls (June vs August). LH concentrations of both groups reached maxima in July; however, in the experimental group, LH levels declined much faster than in controls and then rose again in October-November. Testosterone (T) concentrations of M-fed bucks were elevated 2 months ahead of controls. Melatonin treatment had no significant effect on seasonal variation of T3, or T4. No seasonal rhythm of cortisol was seen in either group and no detectable effect of M was evident. No statistical differences in levels of alkaline phosphatase were seen between groups, although concentrations in experimental bucks sharply dropped to basal levels two months ahead of controls.

Administration, Oral↗
PubMed1986

Hormones in milk.

Protein hormones (especially prolactin) and steroid hormones (gestagens, estrogens, corticoids, and androgens) can be detected by bioassay and radioimmunoassay in milk in a variety of species. In addition, milk contains vitamin D and beta-casomorphins (opiate-like peptides). It has been assumed that most of the hormones are transferred into milk by diffusion. However, evidence is available for active mechanisms like those for progesterone in goats and prolactin in cows. Most of the hormone profiles in milk are similar to the ones in blood plasma. Hormone concentrations in milk seem to be a good estimate of the average hormone content in plasma, especially for the measurement of longer-lasting secretory activities like progesterone and estrogen release during the estrous cycle or seasonal changes of prolactin in ruminants. Determination of progesterone and estrone sulfate in milk serves as a diagnostic tool in fertility control, especially in cows. Enzyme immunoassay kits are available for this monitoring purpose. Exogenously administered hormones are also transferred into milk. Residue studies have shown that the dilution is so great that it may be assumed that there is no potential risk for the consumer.

Androgens↗
PubMed1985

An opioid antagonist stimulates myometrial activity in early postpartum cows.

The influence of the opioid antagonist naltrexone on myometrial activity of cows was tested during the early postpartum period, when uterine contractions are a highly sensitive indicator of oxytocin actions. Registering intrauterine pressure oscillations in five first calf heifers revealed that myometrial activity was enhanced after naltrexone was administered (0.02 mg/kg BW). However, plasma concentrations of oxytocin were not consistently elevated. In addition, naltrexone did not reliably potentiate the suckling-induced peak of oxytocin release in plasma. In all cases, naltrexone injections caused increases in the cows' respiratory rates and distinct behavioral changes during the first days postpartum, but not later. We conclude that: 1) In the early postpartum period, an inhibitory opioidergic control of myometrial activity may exist in cattle. 2) This control does not seem to be caused by a change in circulating oxytocin levels. 3) Opioids may exert an inhibitory influence on respiratory functions in cattle.

Journal Article↗
PubMed1985

Oxytocin determination in steroid producing tissues and in vitro production in ovarian follicles.

Immunoreactive oxytocin was measured in ovaries (corpus luteum and follicular fluid) and adrenals of cows, and in testes, seminal vesicles, prostate gland and adrenals of bulls. Secretion of oxytocin was further measured after culture of whole follicles, granulosa cells and theca tissue. Concentrations of oxytocin increased in corpora lutea of cycling cattle until mid-luteal phase (447 +/- 93 ng/g wet weight) and decreased afterwards. Low concentrations were found in corpora lutea of pregnant animals (6 +/- 3 ng/g wet weight). Follicular fluid contains some oxytocin (on average 42-108 pg/ml) but concentrations were significantly higher in the fluid of ovarian cysts (190 pg/ml). After culture of follicles the amount of oxytocin released into the medium increased indicating de novo synthesis. The granulosa cells were the main source of follicular oxytocin. Production increased during luteinization indicating that luteinization is an important step for the production of oxytocin in ovaries. Tissues of testes (65 +/- 10 pg/g wet weight) and adrenals from cows (122 +/- 39 pg/g wet weight) and bulls (111 +/- 2 pg/g wet weight) contained oxytocin but at much lower concentrations compared to corpus luteum tissue. About 10 times higher concentrations of oxytocin were measured in the adrenal medulla (717 +/- 96 pg/g wet weight) compared to the cortex (72 +/- 11 pg/g wet weight). Seminal vesicles and prostate gland contained no measurable amounts of oxytocin (less than 5 pg/g wet weight).

Adrenal Glands↗
PubMed1985

Immunocytochemical demonstration of oxytocin in bovine ovarian tissues.

The presence of oxytocin in ovarian tissue was examined immunocytochemically. Bovine antral follicles and corpora lutea were fixed with glutaraldehyde, picric acid and acetic acid fixative and immuno-stained by the indirect peroxidase-antiperoxidase (PAP) technique. Immunoreactive oxytocin was demonstrated in the granulosa cells of small and large follicles, in the granulosa-lutein cells of the young corpus luteum and in the large luteal cells of the mature corpus luteum. The regressing corpus luteum was not stainable. It is discussed that these findings additionally support the view that oxytocin is actually synthesized in ovarian tissues.

Animals↗
PubMed1985

Evidence for the secretion of immunoreactive neurophysin I in addition to oxytocin from the ovary in cattle.

In Exp. I, blood samples were collected simultaneously from the posterior vena cava and jugular vein or aorta from 7 heifers every 5-20 min for 2-5 h. Concomitant pulsatile secretion of oxytocin and immunoreactive neurophysin I was detected in the vena cava, but not in the jugular vein or aorta. Concentrations of oxytocin and immunoreactive neurophysin increased earlier and were higher in the vena cava than in the jugular vein or aorta after the injection of a luteolytic dose of prostaglandin F-2 alpha analogue during the mid-luteal phase of the oestrous cycle, demonstrating its ovarian but not pituitary origin. In Exp. II, blood samples were collected from the jugular vein every 12 h during 1 week after oestrus. Follicular growth had been stimulated during the preceding oestrous cycle with PMSG (10 heifers and cows) or with FSH (5 animals); 6 heifers served as controls. There was a high correlation between the number of follicles or CL and the increase in oxytocin and immunoreactive neurophysin I. Although PMSG had a greater luteotrophic effect than did FSH on progesterone secretion, a similar stimulation of oxytocin and immunoreactive neurophysin I was not observed. It is concluded that immunoreactive neurophysin I and oxytocin are secreted from the ovary in concentrations dependent upon the number of corpora lutea (and of follicles) present. During the mid-luteal period the secretion occurs in a concomitant pulsatile fashion.

Animals↗
PubMed1985

Activity of the genital tract and plasma levels of oxytocin and cortisol at the time of mating in the ewe.

Experiments were conducted in the ewe to determine the effects of mating on the activity of the genital tract and on blood levels of oxytocin and cortisol. The activity of the uterus and cervix was recorded by electromyography, oxytocin was measured by radioimmunoassay, and cortisol by high performance liquid chromatography. Mating itself did not increase circulating oxytocin or cortisol; uterine motility remained unchanged during and after copulation but the cervix was significantly stimulated during teasing and after copulation. It is suggested that increased cervical activity resulting from adrenergic mechanisms may facilitate the generation of a cervical reserve of spermatozoa.

Animals↗
PubMed1984

Circulating concentrations of oxytocin during pregnancy in ewes.

Oxytocin and progesterone were measured radioimmunologically during a control cycle, early pregnancy and during several time courses until term in 4 ewes of a local Maroccan breed of sheep. Oxytocin concentrations increased in a similar matter after day 3-4 of the control cycle or after mating and decreased on days 13-15 of early pregnancy about 2 days earlier than during the oestrous cycle. After days 18-19 of pregnancy oxytocin concentrations remained low until term at concentrations as observed during the non-luteal phase of the oestrous cycle. Contrary progesterone concentrations remained high throughout gestation. Maternal recognition of pregnancy seems to have only a slight effect on the secretion pattern of oxytocin for few days after day 12. The results indicate a similar unknown mechanism during the cycle and early pregnancy for the vanishing oxytocin secretion and perhaps synthesis.

Animals↗
PubMed1984

Plasma gonadotrophin concentrations during the oestrous cycle and after ovariectomy in two breeds of sheep with low and high fecundity.

LH and FSH concentrations were measured during the oestrous cycle in two local Moroccan breeds of sheep with low (Timahdite: 1 CL/cycle) and high (D'man: 3 CL/cycle) ovulation rates. Twenty ewes were used from each breed and blood was collected at 3- or 6-h intervals from 5-4 days before oestrus up to Day 14 of the new cycle, when 4 D'man and 4 Timahdite ewes were ovariectomized. After surgery, blood sampling was continued at 6-h intervals for 2 weeks. (1) The mean basal concentration of LH, the maximum value of the preovulatory LH surge and the area under the curve were significantly higher (P less than 0.05) in Timahdite than in D'man ewes. (2) The pattern of FSH in each breed showed no clear basal level but a periodic succession of peaks with variable amplitudes. The first and highest peak corresponded with the preovulatory LH surge. The 2nd peak followed immediately after the first peak and reached its maximum 24-30 h later. The 3rd peak was flatter and occurred around Day 6 of the cycle. The 4th peak was observed around Day 10 of the cycle and showed the lowest amplitude. The 5th and last peak occurred 66-87 h before the next preovulatory surge. (3) FSH concentrations were higher in the prolific D'man than in Timahdite ewes around the time of oestrus (pro-oestrous peak, preovulatory surge and the 2nd peak). The drop in FSH concentrations observed in D'man ewes before the preovulatory surge was more pronounced and started later.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Pulsatile secretion of gonadotrophins, ovarian steroids and ovarian oxytocin during the luteal phase of the oestrous cycle in the cow.

All hormones were determined in blood samples collected simultaneously from the caudal vena cava and jugular vein at 20-min intervals for 12 h during the early (Day 4) and mid- (approximately Day 11) luteal phases of the oestrous cycle in 7 cows. Mean concentrations of oestradiol, progesterone and oxytocin were greater (P less than 0.01) in the vena cava than in the jugular vein. Pulses of these hormones were also more easily identifiable in the vena cava. The frequency of LH pulses was higher (P less than 0.01) during the early luteal than during the mid-luteal phase (8.0 versus 3.6 pulses/12 h). During both phases, 90-96% of all LH pulses were followed within 60 min by a pulse of oestradiol. Basal concentration and amplitude of oestradiol pulses were greater (P less than 0.05) during the early than during the mid-luteal phase. The frequency of FSH pulses was similar to that of LH during the early luteal phase (8.5 and 8.0 pulses/12 h) but was greater (P less than 0.01) than that of LH during the mid-luteal phase (6.3 versus 3.6 pulses/12 h). Thus, 41% more (P less than 0.01) FSH pulses than LH pulses were observed during the mid-luteal phase. However, the separate FSH pulses were associated with low-amplitude short-duration pulses of LH as clarified by an additional study (in 3 cows) using 5-min sampling intervals: 90-100% of all LH/FSH pulses and separate FSH pulses were secreted either concomitantly with or followed by a pulse of progesterone. However, no separate FSH pulses were associated with a pulse of oestradiol. Basal concentration and amplitude of progesterone were greater (P less than 0.01) during the mid-luteal than during the early luteal phase. The frequency of oxytocin pulses was similar to that of progesterone during the mid-luteal but not during the early luteal phase. During the mid-luteal phase 97% of all oxytocin pulses were associated with a pulse of progesterone. It is concluded that (1) separate FSH pulses are secreted in addition to parallel LH and FSH pulses during the mid-luteal phase; therefore, the frequency of secretion of LH may be modulated to a greater extent by ovarian steroids than is FSH pulse frequency; (2) pulses of progesterone are probably a result of stimulation by pulses of FSH and/or LH whereas pulses of oestradiol are caused by LH pulses; (3) ovarian oxytocin and progesterone are secreted concomitantly during the mid-luteal phase of the oestrous cycle.

Animals↗
PubMed1984

Pulsatile secretion of gonadotrophins, ovarian steroids and ovarian oxytocin during prostaglandin-induced regression of the corpus luteum in the cow.

A luteolytic dose (500 micrograms) of cloprostenol was given on Day 12 of the oestrous cycle to 5 heifers. Blood samples were collected simultaneously from the caudal vena cava and jugular vein at 5-20-min intervals from -6 to 0 (control period), 0 to 12 and 24 to 36 h after PG injection. Pulses of LH were secreted concomitantly with pulses of FSH during all sampling periods. However, during the control period separate FSH pulses were detected resulting in a shorter (P less than 0.01) interpulse interval for FSH than LH (93 versus 248 min). LH and FSH pulse frequencies increased (P less than 0.01) beginning 1-3 h after PG to interpulse intervals of 59 and 63 min, respectively, and continued to be maintained 24-36 h after PG. Concomitantly there was a 2-3-fold increase (P less than 0.01) in basal concentrations and pulse amplitude for LH (but not FSH). FSH basal concentrations and pulse amplitudes decreased (P less than 0.05) in 3 heifers 24-36 h after PG. Pulsatile secretion of oestradiol was observed at frequencies similar to LH during the periods 4-12 h (3 heifers) and 24-36 h (2 heifers) after PG, respectively, resulting in higher (P less than 0.05) mean oestradiol concentrations. Progesterone concentrations in the vena cava increased (P less than 0.01) 5-10 min after PG but decreased (P less than 0.01) 67% by 20 min after PG. This decrease was followed by a rise (P less than 0.05) beginning 2-3 h after PG and lasting for an average of 3.3 h.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

The role of steroid hormones, prolactin and placental lactogen on mammary gland development in ewes and heifers.

In the first part of the investigations the interaction between oestradiol-17 beta, progesterone and prolactin on the formation of the lobuloalveolar structure of the mammary gland was studied in 21 nulliparous intact postpubertal ewes. Tissue specimens of the mammary gland were evaluated by light microscopical examination and prolactin was measured in blood samples. Combined treatment with oestradiol and progesterone induced physiological development of the lobuloalveolar structure of the mammary gland in the presence of prolactin. Suppression of prolactin by bromocriptine prevented this effect. Treatment with progesterone alone was not effective and revealed histological structures comparable to the controls. The interaction of oestradiol-17 beta with prolactin appears to be a main trigger for mammary gland development. In the second part of the investigations the effect of bromocriptine treatment during pregnancy on mammary gland development was studied in primigravid ewes and heifers. Mammary gland specimens were obtained for light and electron microscopical evaluation in ewes and heifers 5 and 10 days respectively before the expected date of parturition. Concentrations of prolactin and ovine placental lactogen were determined by radioimmunoassay. Bromocriptine treatment suppressed prolactin concentrations in ewes to minimal values but did not affect ovine placental lactogen concentrations. The histological evaluation revealed almost comparable stages of mammogenesis in both ewes and heifers. This effect can be attributed, at least in ewes, to the action of placental lactogen on mammogenesis. Placental lactogen might therefore be of physiological relevance during mammogenesis.

Animals↗
PubMed1984

Oxytocin secretion during milking in dairy cows with regard to the variation and importance of a threshold level for milk removal.

Oxytocin secretion in dairy cows was measured during milking by means of a specific radioimmunoassay. Basal oxytocin concentrations before milking recorded from 147 milkings from 21 cows, where an assay method with enhanced sensitivity was employed, were 1.5 +/- 0.6 pmol/l and there was no evidence for any conditioned release of oxytocin. A 1-min manual stimulation before milking evoked a variable but distinct increase in oxytocin concentrations in 188 out of 195 milkings performed using 29 cows. Despite the high variation in absolute concentrations five types of typical secretion pattern could be distinguished. There was no obvious relationship between patterns or absolute concentrations of oxytocin and milk-flow characteristics. Evidence is given that milk ejection seems to follow the threshold principle in that small releases of oxytocin up to a range of 3-5 pmol/l plasma are sufficient to evoke maximum milk ejection.

Animals↗
PubMed1984

Secretion of oxytocin and milk removal as affected by milking cows with and without manual stimulation.

Milking cows with a 1-min manual stimulation (treatment 1) and without any udder preparation (treatment 2) was compared by application of an improved, highly sensitive radioimmunoassay for oxytocin and recordings of milk-flow curves. Both treatments caused the release of oxytocin, but treatment 2 generally seemed to be less efficient. Milking characteristics supported the advantage of manual stimulation; milk yield and milk flow were significantly higher, while 'machine-on' time was shorter. This clearly indicates the importance of the right timing of release of oxytocin before commencement of milking. Substitution of stimulation by an i.v. injection of 0.5 i.u. oxytocin (treatment 3) resulted in milking parameters very similar to those of treatment 2. This implies that manual stimulation has other effects besides the secretion of oxytocin which are also responsible for optimal milk removal.

Animals↗
PubMed1984

[Intersexuality in the horse. Morphologic, hormone analytic and cytogenetic studies in an Arabohaflinger horse].

A case of intersexuality in an arabo-haflinger horse is described. The external genitalia consisted of mammary gland, vulva and hypertrophic clitoris; the inner genitalia of rudimental testes. The sexual behaviour was typically male-like. The chromosome analysis showed the female karyotype 64,XX. The presence of testes in a genetically female animal is explained by translocation of an Y-chromosome fragment bearing the gene for the H-Y-antigen.

Animals↗