Biomedical subjects

D Schams

Publications and source records attributed to D Schams.

At least 109 records · Page 6Linked to original sources

PubMed1991

Antler cycle and endocrine parameters in male axis deer (Axis axis): seasonal levels of LH, FSH, testosterone, and prolactin and results of GnRH and ACTH challenge tests.

1. Antler cycles of six adult male axis deer of southern Texas were relatively well synchronized within the herd. The old antlers were cast from December to March and regenerated antlers polished between March and June. The rutting season occurred in June and July. 2. LH and FSH exhibited little seasonal variation (LH 0.7-1.3 ng/ml; FSH 32-65 ng/ml). Prolactin levels were lowest in December (20 ng/ml) and highest in June (115 ng/ml). Testosterone concentrations exhibited a distinct seasonal pattern: minimum in December (0.1 ng/ml) and maximum in May (1.75 ng/ml). 3. After GnRH challenge (100 micrograms given i.m. in November), maximal LH levels (reached 40-60 min after injection), varied from 7.7 to 11.2 ng/ml, and T levels varied from 1.3 to 1.6 ng/ml. 4. Twenty I.U. of ACTH (given in March), elevated cortisol levels from 4-8 micrograms/dl (pretreatment) to 16-21 micrograms/dl (140 min post-administration).

Adrenocorticotropic Hormone↗

PubMed1991

Lactational changes in oxytocin release, intramammary pressure and milking characteristics in dairy cows.

Two experiments were conducted to investigate possible changes of milking-related oxytocin release (Expt 1) and of intramammary pressure and milking characteristics (Expt 2) throughout entire lactations in German Braunvieh dairy cows. Mean oxytocin concentrations after stimulation at onset of milking increased from 18.3 +/- 15.9 to 30.7 +/- 24.1 pg/ml in Expt 1 and decreased from 23.9 +/- 17.6 to 15.4 +/- 9.1 pg/ml in Expt 2, respectively, but remained above the level necessary to elicit complete milk ejection in both trials. Premilking baseline intramammary pressure had its maximum in early lactation until about month 4 and then decreased to approximately 50% of its initial level. Ejection pressure followed a similar pattern, but dropped only to approximately 75% of its maximum. This was due to the constant elevation of pressure increase, reaching its highest level in late lactation. Time from commencement of stimulation until maximum pressure exceeded 1 min in almost all instances even in early lactation and increased throughout lactation. Despite the normal decrease of milk yield average milk flow fell only slightly while maximum flow rate remained almost constant. Pressure increase, milk yield and milk flow were not different after 1 min and after extended stimulation. Thus there were no indications of a decreasing sensitivity of the milk ejection reflex during lactation, and milking characteristics were positively affected by intense teat stimulation. Suggestions for practical dairying are made.

Animals↗

PubMed1991

Changes in concentrations of insulin-like growth factor 1, insulin and growth hormone in bovine mammary gland secretion ante and post partum.

Concentrations of insulin-like growth factor 1 (IGF-1), insulin and growth hormone were measured in the secretion of the bovine mammary gland from day 70 ante partum until 6 d post partum. Highest levels were found during the last 2 weeks ante partum followed by a rapid decrease during the first milkings post partum. The association of IGF-1 with its binding proteins in milk was analysed and striking differences were found in the distribution of bound and free IGF-1. IGF-1 appeared mainly in the bound form (91%) at days 40-2 ante partum. Free IGF-1 preponderated in the first milkings post partum (73%) and changed again to about 85% in the bound form after day 4 post partum. A slightly acidic pH (6.3) of the secretion was correlated with high amounts of free IGF-1. Gel filtration experiments revealed a possible pH-dependent mechanism for the binding of IGF-1 to its binding proteins in milk.

Animals↗

PubMed1991

Effects of alpha- and beta-adrenergic agonists on intramammary pressure and milk flow in dairy cows.

alpha-Adrenergic mimetics inhibit milk removal whereas beta-adrenergic mimetics have a favourable effect upon milk removal in dairy cows. This work aimed to relate these effects to the milk ejection reflex mechanism and/or milk flow from the cisternal cavities only. The alpha-adrenergic agonist phenylephrine and the beta-adrenergic agonist isoproterenol were injected prior to and after milk ejection. Applied after milk ejection, the phenylephrine treatment reduced intramammary pressure (IMP) and milk yield markedly. Phenylephrine application before milk ejection prevented IMP from rising during teat stimulation or after oxytocin injection. Milking produced small amounts of milk at minimal milk flow rates. The very different responses to phenylephrine application prior to and after milk ejection indicate separate adrenergic inhibitory mechanisms for milk ejection and milk flow. The application of the beta-adrenergic agonist isoproterenol did not alter the IMP. Nevertheless, this compound improved milk removal by increasing milk flow. The observation of bimodal milk flow at milkings without preceding teat stimulation indicates a delayed milk ejection. Isoproterenol injection without teat stimulation enhanced milk flow rates, but the bimodality remained unchanged. We conclude that isoproterenol enhances milk flow without affecting milk ejection.

Adrenergic alpha-Agonists↗

PubMed1991

Evidence for relaxin and progesterone synchronous secretion on days 13 to 17 of the oestrous cycle in sows.

Concentrations of relaxin in both the utero-ovarian vein (UOV) and jugular vein (JV) as well as those of progesterone and prostaglandin F2 alpha in the UOV were studied on Days 13-17 of the oestrous cycle in sows. Mean relaxin plasma concentrations in the UOV and JV were correlated (r = 0.55; P less than 0.001) and were significantly higher (P less than 0.01) in the UOV (1.67 +/- 0.07 ng/ml), than in the JV (0.59 +/- 0.1 ng/ml). The great similarity between relaxin and progesterone profiles was ascertained (r = 0.57; P less than 0.001). The steep decrease of progesterone plasma concentration on the day of luteolysis was observed together with synchronous relaxin concentration decline. A significant correlation between relaxin and PGF2 alpha plasma concentration was demonstrated one day before luteolysis (r = 0.41; P less than 0.001).

Animals↗

PubMed1991

Oxytocin stimulates progesterone release from microdialyzed bovine corpus luteum in vitro.

A microdialysis system (MDS) was implanted in corpora lutea (CL) from cows (Days 5-7, 8-12, and 15-18 of the estrous cycle); the CL were maintained in organ culture chambers. With this system, active substances can be applied, and a collection of steroids released from luteal cells surrounding the microcapillary (cut-off point = 100 kDa) is possible, while luteal cells maintain cell-to-cell contact. Spontaneous pulses of progesterone release were observed in 90% of control (perfused with Ringer's solution only) at 60-80 min intervals. The infusion of bovine LH (bLH) for 20 min (0.1-10 micrograms/ml) stimulated dose-dependent release of progesterone. Both results indicate that the CL maintains the activity of progesterone release and the ability to respond to LH stimulation in this system. Oxytocin (1-100 microM) also stimulated progesterone release in a dose-dependent manner. Preexposure with oxytocin antagonist blocked the stimulatory effect of oxytocin (p less than 0.01) but not of LH (p less than 0.05), confirming the specificity of the effect. When CL were prestimulated with a low dose of oxytocin (1 microM, 20 min) twice before bLH application, the release of progesterone by bLH (1 micrograms/ml, 20 min) was more pronounced (p less than 0.05). A long-term infusion (3 h) with oxytocin and/or bLH stimulated the release of progesterone for the whole period of time. Oxytocin was most stimulative during the early luteal phase (Days 5-7) and decreased continuously from Days 8-12 to Days 15-18.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Effect of recombinant bovine somatotropin (BST) on physiological parameters and on milk production in German Fleckvieh cows.

The efficacy of injecting primiparous cows of a dual purpose breed (Deutsches Fleckvieh) with a BST prolonged release formulation (500 mg Sometribove s.c.) was tested in a cross-over design. Seven cows were given 500 mg BST in the 10th through 19th week of lactation and a placebo in the 24th through 33rd week. A second group of seven cows received a placebo in the 10th through 19th week and BST in the 24th through 33rd week. Blood samples were taken from the jugular vein (via a permanent cannula) in the 13th, 17th, 23rd, 27th and 31st week of lactation over a period of 24 hrs at 30 min intervals. During the periods of BST treatment the amount of FCM (amount of milk corrected to 4% fat content) was higher in treated than in non-treated animals by 3.6 kg (19.8%) and 3.2 kg (22.5%) respectively. Milk fat levels were elevated significantly during both treatment periods. Milk protein concentration showed a significant rise during the second half of lactation only. There was no influence on lactose content. Blood concentration of somatotropin and IGF-I rose during treatment by a factor of 3-4. Insulin, T3, T4 and FTI as well as glucose, urea and GOT showed no changes or changes within physiological ranges. Free fatty acids and beta-hydroxybutyrate rose during treatment.

Animals↗

PubMed1991

Changes in hormones, metabolites, and milk after treatment with sometribove (recombinant methionyl bST) in Deutsches Fleckvieh and German black and white cows.

Twelve second-lactation Deutsches Fleckvieh cows, (FV, a dual-purpose breed) and 12 German Black and White (BW, a dairy breed) were used to evaluate similarities and differences in the response to a prolonged-release formulation of sometribove (N-methionyl bovine somatotropin, bST). Cows were milked twice daily and fed a basic diet (70% corn silage, 30% alfalfa hay) ad libitum plus 1 kg of concentrate. Additionally, concentrates and supplements were offered at the rate of 1 kg for each 22 kg of milk produced above 12 kg/d. Six cows of each breed were treated s.c. with 500 mg of sometribove at 14-d intervals from wk 9 to 29 postpartum (pp). Blood was collected by jugular vein puncture once weekly from wk 7 to 33 pp and daily for 14 d after the first and last (11th) injection of bST. Somatotropin (ST), insulin-like growth factor I (IGF-I), insulin, thyroid hormones, nonesterified fatty acids (NEFA), liver enzymes, and blood metabolites were evaluated. During bST treatment, plasma ST increased significantly on d 7 in both breeds and then decreased on d 14 after injection. Plasma IGF-I was positively correlated with ST. Plasma NEFA were high on d 7 and decreased on d 14. In response to bST, the average milk yield increased for FV and BW cows by 5.1 kg/d (29.7%) and 5.0 kg/d (28%), respectively, and 4% fat-corrected milk (FCM) increased by 5.0 kg/d (28%) and 5.3 kg/d (19.9%), respectively. Milk content of fat, protein, lactose, number of somatic cells, and body weight were similar across treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Growth hormone, IGF-I and insulin in mammary gland secretion before and after parturition and possibility of their transfer into the calf.

The aim of this study was to monitor the changes of growth hormone (GH), insulin-like growth factor I (IGF-I) and insulin in the secretion of the bovine mammary gland from day 70 ante partum (AP) till 6 days post partum (PP) and during entire lactation period. For comparable reasons additional blood concentrations were evaluated. The association of IGF-I with its binding proteins in milk was analysed. In a further experiment the possible transfer of IGF-I and insulin into the peripheral circulation of calves was evaluated after application of an enriched and from content defined colostrum pool. The hormones were determined by RIA. Highest level of IGF-I and insulin in milk were found 2 weeks AP followed by a rapid decrease during the first milkings PP. Blood concentrations were much lower and decreased at that time. Striking differences were found in the distribution of bound and free IGF-I AP compared with the first milkings (colostrum) PP. Most of the IGF-I was in a free form (not associated with binding proteins) in colostrum which contrasted to the secretion AP or 4 days after parturition or during entire lactation. Application of a colostrum pool (4.62 mg/2 1 vs milk 0.042 mg/2 l) to calves 6 h after parturition did not increase peripheral blood levels of IGF-I in contrast to insulin. Local effects of the peptide hormones in colostrum to the mammary gland and intestinal tract of the calf are assumed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

[The reproductive function in experimentally-produced monozygotic twin bulls].

Reproductive functions were evaluated in 12 experimentally derived monozygotic cattle twins (6 pairs). In 4 twin pairs GnRH (20 micrograms Receptal i.m.) was administered in monthly intervals from 6 through 12 months of age. LH-secretion was determined by radioimmunoassay up to 6 hours after the GnRH-challenge in hourly collected peripheral blood samples. In 5 twin pairs (age 14 to 20 months) semen was collected 5 times and processed for cryoconservation. In fresh and in frozen-thawed semen samples sperm motility was determined by means of a computerized system. Twins showed a remarkable uniform response to the GnRH-challenge. One set of twins (HF-breed) had a significantly reduced response compared to the other pairs (DFV-breed). Both individuals of this particular pair had a low percentage of progressively motile spermatozoa. In pairs with physiological sperm motility, variance of this parameter within pairs and between pairs was not different. In contrast, twin uniformity concerning the average velocity of motile spermatozoa was high; differences between set of twins explained most of the total variance. According to this study, reproductive parameters in monozygotic cattle twins are strongly influenced by twin uniformity.

Animals↗

PubMed1990

[Control of the use of bovine somatotropin (bST) by the determination of bST and insulin-like growth factor I (IGF-I) in blood and milk of cows].

bST, a milk production-enhancing compound not yet registered in the EG and the USA, has been evaluated as safe for the consumer. Nevertheless, actual discussions include a possible ban of applications; therefore, effective measures of control are demanded. The evaluation of bST plus IGF-I in blood only allows a monitoring of bST treatment. Under the condition of two blood samplings from each cow with a 7-day interval and the favorable experimental design (1. sampling rigorous on days 4 or 6 after injection of a bST depot preparation), an efficiency of 96% correct evaluations could be obtained; under field conditions, despite analytical efforts, about 20% false estimations must be taken into account. There is no means of monitoring milk and other products of cows treated with bST, hence analytical measures for the control of imports seems to be useless.

Animals↗

PubMed1990

Plasma LH, FSH, testosterone, prolactin and androstenedione in male white-tailed deer after ACTH and dexamethasone administration.

1. In order to investigate the role of the adrenocortical system in the regulation of plasma levels of reproductive hormones, adult male white-tailed deer (five intact and one castrated) from a captive herd were sedated with xylazine and ketamine and then challenged with various doses of ACTH with and without dexamethasone (DX) pretreatment. 2. Plasma levels of LH, testosterone (T), FSH, prolactin (PRL) and androstenedione (A) were determined by RIA in serial samples taken from the jugular vein. 3. An increase of A levels detected after ACTH in both intact and castrated deer indicated stimulation of secretion of adrenal androgens by ACTH. 4. No effect on FSH and PRL levels was observed in either group. 5. A significant decline of LH and T observed in various treatments could not be attributed to ACTH or DX administration. It is speculated that the decrease may be caused by anaesthetics which alleviate the stress induced in deer by the pre-immobilization activities.

Adrenal Cortex↗

PubMed1990

Development of a sensitive enzyme immunoassay for LH determination in bovine plasma using the streptavidin-biotin technique.

Using the biotin-streptavidin amplification technique, highly sensitive specific second-antibody enzyme immunoassays for determining LH in bovine plasma with long (48 h) and short (4 h) incubation periods were developed. Biotin was linked to bLH by the N-hydroxysuccinimide method and the product (biotinyl-bLH) used to bridge between streptavidin-peroxidase and the immobilised bLH antibody in competitive tests. The assays were validated and their performance compared with a radioimmunoassay currently in use. The sensitivities of the long and short incubation enzyme immunoassays (8 pg and 15 pg/well, respectively) were superior to that of 5-day incubation radioimmunoassay (100 pg/tube). Plasma interference in both assays were acceptable and volumes of 5 to 40 microliters gave parallel standard curves and comparable LH levels, 10-20 microliters plasma was sufficient to measure LH baseline levels by the long incubation enzyme immunoassay. The mean recovery of added standard bLH to plasma samples containing different endogenous LH was greater than 90% (range 91.7-112) in both assays. The intra- and inter-assay variations of both assays were less than 10 and 17%, respectively. When both enzyme immunoassay and radioimmunoassay were used to measure LH in cyclic cows, the basal levels measured by enzyme immunoassay were lower than that measured by radioimmunoassay. Enzyme immunoassay offers an attractive alternative to the lengthy radioimmunoassay in current usage, with an added advantage of employing non-isotopic label.

Animals↗

PubMed1990

Tissue concentration, mRNA expression and stimulation of IGF-I in luteal tissue during the oestrous cycle and pregnancy of cows.

The expression of IGF-I in bovine luteal tissue was demonstrated by parallel measurement of IGF-I tissue concentration and its mRNA; highest synthesis was observed during Days 12-17 of the cycle and the first months of pregnancy. Tissue levels of IGF-I increased from Days 1-5 to Days 12-17 of the cycle followed by a rapid decrease at luteolysis; there was a continuous decline from early pregnancy until Months 6-9. Microdialysis perfusion experiments with corpora lutea in vitro at Days 8-11 of the cycle revealed a major effect: release of progesterone and oxytocin were highly stimulated in a dose-dependent manner. We suggest that IGF-I could be important in regulating the function of the bovine corpus luteum and may act in an autocrine/paracrine way.

Animals↗

PubMed1990

Influence of mating and intra-uterine oestradiol infusion on peripheral oxytocin concentrations in the sow.

Oxytocin concentrations were measured radioimmunologically in sows on the day of standing oestrus over a 6-h period (controls, n = 6) or 1 h before and 5 h after mating (n = 5) or transcervical infusion of either 100 ml saline (0.9% (w/v) NaCl, n = 7) or saline plus 10 micrograms oestradiol (simulation of seminal oestrogens, n = 5). In the controls, oxytocin was low, at around 1.0 pmol/l, throughout the investigation period. Similarly, saline infusion did not lead to a noticeable change in oxytocin concentrations in six out of seven sows. In one sow, however, infusion led to a maximum of 86 pmol/l at 1 min after infusion. Oestradiol led to no immediate increase in oxytocin concentrations. Later in the post-treatment period (2-5 h) they were only slightly increased (1 pmol/l vs 3 pmol/l). All mated sows reacted with a rapid and clear increase in oxytocin. Maximal concentrations (42.0 +/- 5.1 pmol/l; mean +/- S.E.M.) appeared 2 min after the onset of ejaculation. Clearly increased concentrations were found for 40 min. It was concluded that mating specifically leads to a rise in oxytocin, probably due to both mechanical and pheromonal stimuli provided by the boar.

Animals↗

PubMed1990

[Effects of a metabolic endurance test developed for the constitution examination of young bulls on spermatologic and endocrine parameters].

The purpose of this study was to examine the influence of an eight day starvation period on semen characteristics and some endocrine parameters of young bulls. The experiments were performed with 18 bulls in two trials showing the following set-up: pre-treatment period (7 or 20 days), starvation period (8 days), realimentation period (3 days) and control period (64 days). During the pre-treatment period and the control period the bulls obtained a well-balanced food-ration, during the period of starvation only 2 kg straw daily. During the starvation period the bulls lost 6% of their bodyweight. No influence on general health could be noticed. The concentrations of testosterone, LH, bovine growth hormone, insulin and insulin-like growth factor decreased significantly during or after the period of starvation. There was no clear influence in volume, sperm density and total number of sperm due to the metabolic stress during the hunger period. The initial progressive motility of sperm was not affected. The percentage of morphological abnormal spermatozoa increased 45-55 days after the hunger period. Simultaneously the semen freezability was decreased. An influence on the acrosomal morphology of frozen/thawed spermatozoa could not be obtained. The concentration of fructose, citric acid and glycerylphosphorylcholine (GPC) of the seminal plasma was insignificantly influenced during the period of starvation. The realimentation caused a stimulating effect on the secretion mainly of GPC.

Animals↗

PubMed1990

[Concentration of IGF-I and estradiol-17beta in the blood plasma of pregnant cattle].

Blood samples were collected from pregnant cows, heifers and also from non pregnant cows serving as controls. The determination of insulin-like-growth-factor-I (IGF-I) and estradiol-17 beta (E2) were performed immunologically. In the non pregnant cows E2 remained unchanged. IGF-I decreased around parturition and increased again commencing the 6th week of lactation. Compared to nonpregnant animals E2 but not IGF-I was slightly elevated during the first 10 weeks of pregnancy. During the 10th up to 20th week of pregnancy the mean values of IGF-I were increased as well as the ones of E2. During the late pregnancy the values of IGF-I in heifers are obviously more elevated as in lactating pregnant or non-pregnant cows; analogous high values were determined in pregnant cows only during the dry period. Before parturition even a negative correlation exists between IGF-I and E2. It is concluded that IGF-I is predominantly regulated by other factors.

Animals↗

PubMed1989

Catecholamines, oxytocin and milk removal in dairy cows.

Experiments were designed to study the effects of catecholamines on oxytocin responses and milk removal in dairy cows. Adrenalin, noradrenalin, dopamine, isoproterenol (a beta-adrenoceptor agonist), phentolamine (an alpha-adrenergic blocker) and propranolol (a beta-adrenergic blocker) were infused intravenously. In addition, adrenalin was infused together with phentolamine and/or propranolol. Infusions started 8 min before milking and lasted until the end of milking. In some cases electroshocks (for 5 s) were applied immediately before milking in the absence and presence of phentolamine and propranolol. Adrenalin, noradrenalin and dopamine reduced milk removal, but only if administered in supraphysiological amounts. The effect of adrenalin and electroshocks on milk removal could be inhibited only partly by phentolamine. Inhibition of milk removal was not mediated by reduced oxytocin responses. Enhanced local release of catecholamines from sympathetic nerves was presumably responsible for lowered milk removal in response to electroshocks. Milk removal was facilitated during alpha-adrenergic blockade and during beta-adrenoceptor stimulation.

Animals↗