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Biomedical subjects

D Schams

Publications and source records attributed to D Schams.

At least 163 records · Page 9Linked to original sources
PubMed1983

Circadian and circannual rhythms of LH, FSH, testosterone (T), prolactin, cortisol, T3 and T4 in plasma of mature, male white-tailed deer.

Circadian and circannual rhythm of plasma LH, FSH, testosterone (T), prolactin, cortisol, triiodothyronine (T3) and thyroxine (T4) were investigated in two mature male white-tailed deer. No circadian rhythms were detected. Seasonal levels of LH and FSH were reached in September and October; troughs occur in May and June. Maximal T values were detected in November and December (the time of the rut); minimal levels occur between February and July. Prolactin peaked in May and June; minimal levels were detected between October and February. T3 exhibited two maxima; the first in the May-June period, the second in the September-October period. T4 showed no recognizable circannual rhythm. Cortisol levels were found to be much higher during cold months (December-April) than during the rest of the year. The least variable circadian levels were that of FSH and prolactin, with LH, T4, T3, cortisol and testosterone following in descending order. Cannulation stress might have some effect on the levels of testosterone, LH and cortisol. Correlation between LH and testosterone levels were detected mainly during sexually active periods.

Animals↗
PubMed1983

Are regular activity episodes of the genital tract controlled by pulsatile releases of oxytocin?

The possible control by endogenous oxytocin of the regular activity episodes which occur in the ovine genital tract was assessed in 3 cyclic ewes chronically fitted with intraparietal electrodes. Despite the existence of a pulsatile release of the hormone into plasma, no significant relationships were noticed between the motility events of genital tract and plasma concentrations of oxytocin.

Animals↗
PubMed1983

The effect of active and passive immunization against oxytocin on ovarian cyclicity in ewes.

Active and passive immunization of ewes against oxytocin prolonged the luteal phase of the oestrous cycle, as evaluated by oestrus behaviour and determination of progesterone. Between the animals there was a high variability in response. In general animals with prolonged cycles had lower concentrations of free oxytocin. But in some animals oxytocin antibodies had no effect on cyclicity. Therefore, an individual minimal threshold concentration for oxytocin was presumed. In control or treated animals circulating oxytocin concentrations increased parallel with progesterone concentrations but decreased earlier during the mid luteal phase of the cycle. A new increase in oxytocin concentrations was only observed if a new corpus luteum was formed.

Animals↗
PubMed1983

Oxytocin determination by radioimmunoassay. III. Improvement to subpicogram sensitivity and application to blood levels in cyclic cattle.

An improved RIA for measurement of oxytocin in blood is described by using an extraction method with SEP-PAK C18 cartridges, which allows also concentration of the sample, a new antiserum with a higher sensitivity to standard oxytocin and preparation of the standard curve in buffer. The lower limit of assay sensitivity was 0.25 pg/tube, corresponding to 0.25-1.0 pg/ml plasma depending on the amount of plasma extracted. Hence, it was no problem to measure oxytocin basal concentrations in peripheral blood in the range of 0.6-4 pg/ml plasma depending on the stage of the oestrous cycle. The highest oxytocin concentrations occurred during the early and mid-luteal phase. The method has been applied also for samples from women, sheep, pigs and horses. Mean (+/- SD) recovery of oxytocin added to plasma or only buffer after extraction was 71.3 +/- 8.1%, and the coefficient of variation (CV) = 11.4% (n = 27 assays). The intra-assay CV of two control samples was 7.9 +/- 2.8 and 7.8 +/- 2.4% (n = 17 assays). The inter-assay CV of 5 control samples with low and high oxytocin concentrations varied between 10.8 +/- 17.3% (n = 25 assays). The 50% intercept was 2.5 +/- 0.3 pg, CV = 11.3% (n = 29 assays).

Animals↗
PubMed1982

Hormonal responses following treatment with different prostaglandin analogues for estrous cycle regulation in cattle.

The effect of four different prostaglandin F(2)alpha analogues on secretion of the pituitary hormones prolactin, LH, FSH and oxytocin was evaluated in heifers. In addition, the luteolytic activity was measured by means of progesterone concentrations. For the sake of comparison, the corpus luteum of two heifers was enucleated and the effect on the above hormones determined. There seemed to be no differences among the various analogues concerning their luteolytic action on the corpus luteum. No effect on FSH secretion was observed. Basal concentrations of LH increased about 4 - 5 h after injection of the analogues, concurrently with the decrease of progesterone. Enucleation of the corpus luteum was followed by a similar pattern of hormone secretion. Therefore, the increase in LH concentrations did not appear to be a specific effect of the analogues, but was probably a result of the decrease in progesterone concentration. Within twenty minutes after administration of the analogues a clear increase in plasma prolactin (2-4 h) and oxytocin concentrations (1-2 h) could be demonstrated.

Journal Article↗
PubMed1982

Photoperiodicity and circannual levels of LH, FSH, and testosterone in normal and castrated male, white-tailed deer.

To establish the relation between photoperiodicity and the levels of LH, FSH, and testosterone (T) in plasma, three intact and three castrated adult male white-tailed deer were sampled once a month for 2-3 years. The rang of average LH levels in controls varied between 0.8 and 2.0 ng/mL; the levels in castrates were considerably higher, 3.4 to 8.9 ng/mL. Average levels of FSH varied in controls between 25 and 112 ng/mL and in castrates between 141 and 240 ng/mL. A significant correlation between the seasonal time course of LH and FSH was found in castrated, but not in intact bucks. In castrates both gonadotropins exhibit two major elevations coinciding with spring and fall equinoxes in March and September. The seasonal time course of FSH in castrates correlates highly with seasonal levels of FSH in controls. However, the time course of the LH curve in controls is substantially different from the curve in castrates, presumably owing to feedback mechanisms. A possible role of testicular estradiol in this feedback is discussed. In controls, peak T levels are reached in December, i.e., 3 months after maximum levels of FSH and 5 months after peak levels of LH were detected. It appears that male deer undergo two periods of reproductive stimulation (one in the spring, the other in the fall). However, the organism responds with the full range of gonadal and behavioral mechanisms leading to the initiation of the rut only during the fall.

Animals↗
PubMed1982

Annual profiles of reproductive hormones in peripheral plasma of the male roe deer (Capreolus capreolus).

Blood samples were collected from 3 roebucks 1 to 3 times per month during several years to study the relationship between season and concentrations of LH, FSH, testosterone and prolactin. Plasma values of all of these hormones began to increase during the second half of February. LH, FSH and testosterone levels reached a plateau during April. Highest average levels of LH and testosterone were observed before the start of the rutting season (mid-July--mid-August) and steadily declined thereafter. In contrast to LH and testosterone, FSh concentrations decreased 6 weeks earlier, during June, indicating a modulated secretion pattern. Prolactin steadily increased until the beginning of July and then decreased.

Animals↗
PubMed1982

Oxytocin concentrations in peripheral blood during the oestrous cycle and after ovariectomy in two breeds of sheep with low and high fecundity.

Oxytocin was measured radioimmunologically during the oestrous cycle in six ewes of each of two local Moroccan breeds of sheep. Concentrations in both breeds approached the lower limit of the assay (3 pg/ml) from 2 days before oestrus, throughout heat and ovulation until day 2 of the cycle. Oxytocin concentrations then increased in both breeds, the resulting highest levels on days 5-7 were, on average, between 30 and 60 pg/ml in the D'man sheep and 13-31 pg/ml in the Timhadite breed. Oxytocin levels then decreased to about 7 pg/ml in the D'man and about 4-5 pg/ml in the Timhadite breed on days 14-15. After ovariectomy oxytocin concentrations remained at about the limit of detection for a further 19-20 days in both breeds.

Animals↗
PubMed1981

Immunoreactive growth hormone levels during the hormonal induction of lactation and during hand-milking in ewes.

Growth hormone was measured by radioimmunoassay in blood samples collected from ewes during the hormonal induction of lactation and during hand-milking post partum. Ovariectomized ewes were induced to lactate with injections of progesterone + oestradiol benzoate every 3 days for 30 days (priming phase) and then daily injections of dexamethasone for 5 days (trigger phase). The ewes were then milked daily. Immunoreactive GH levels fluctuated considerably but were generally in the range 1-15 ng/ml during all phases of lactation and were unaffected by bromocriptine treatment. Milk yield was unrelated to GH levels. Growth hormone was also measured in blood plasma taken at frequent intervals around the time of milking in lactating ewes approximately 4 weeks post partum. Although a clear prolactin response to milking was observed, there was no indication of a GH response. Although there is probably a minimum requirement for GH for lactation, a relationship between immunoreactive GH levels and milk yields was not established, perhaps because of limitations of the radioimmunoassay to detect all the biologically active GH

Animals↗
PubMed1981

Endocrine patterns associated with puberty in male and female cattle.

In four studies secretion patterns of LH, FSH, prolactin, testosterone and progesterone were measured in male and female cattle to determine endocrine changes associated with sexual maturation. Two periods of increasing gonadotrophin secretion were observed, the second one coinciding with puberty. A short luteal phase of 8-12 days precedes the first oestrus at 10-11 or 14 months of age. The testosterone values of the bulls increased with age from 5-6 months. Prolactin levels in the bulls increased at the time of the first testosterone rise. A frequency of about 1-2 LH and FSH pulses/8 h occurred at 1, 2, 5 and 10 months of age. The pituitary response to GnRH (1 microgram/kg i.v.) was tested in 2 male and 2 female calves at monthly intervals. LH and FSH were released at all ages but a reduced FSH response occurred in both sexes after the 5th month. A small testosterone release was observed as early as 1 month after birth in males similar to those observed after endogenous LH pulses. We conclude that the initiation of puberty in both sexes is controlled by the same neuroendocrine mechanisms. The pituitary gland, ovaries and testes are already able to respond to specific stimuli long before puberty, and they may also be involved indirectly due to changes in the feedback system modulating gonadotrophin secretion.

Aging↗
PubMed1980

The effect of heat exposure on blood serum levels of anterior pituitary hormones in calves, heifers and bulls.

In four experiments male and female calves, heifers and bulls were housed in a climate chamber and exposed to two weeks of hot environmental conditions (30-35 degrees C and 60% relative humidity (RH) during the day; 25 degrees C and 60-70% RH during the night). The animals were subjected to milder conditions (15-18 degrees C and 70% during the day; 12-15 degrees C and 70% during the night) during the two week period preceding and the two weeks following heat exposure. Serum prolactin increased significantly (P < 0.01) when ambient temperature was increased and decreased after reduction of temperature. No changes could be observed for GH, TSH, LH and FSH. There was a significant (P < 0.01) sex difference in GH levels (males < females) in prepubertal calves but this difference was not apparent in older animals.

Age Factors↗
PubMed1980

LH, FSH and progesterone concentrations in peripheral plasma of the female roe deer (Capreolus capreolus) during the rutting season.

Progesterone LH and FSH were measured in the plasma of 4 female roe deer (2 kept with the buck, 2 separated from the buck to prevent mating) from July until the end of September or October, i.e. including the rutting season from the middle of July to the middle of August. At least two distinct peaks of LH and FSH were observed before the first small progesterone increase lasting for about 5 days in late July. The next clear LH peak and, slight individual variations, FSH peak occurred exactly when progesterone values and fallen and before they rose again in a major elevation, i.e. after ovulation. LH and, with some variations, FSH values were generally basal while progesterone was high during the rest of the study. There were no obvious differences in hormone pattern in pregnant and non-pregnant animals.

Animals↗
PubMed1980

Adaptation of the cytohistochemical luteinizing hormone assay for measurement in bovine blood.

The highly sensitive cytohistochemical assay was adapted for LH measurements in peripheral blood of cattle. The reducing ability of rat theca lutein tissue exposed to bovine LH was estimated by scanning and integrating microphotometry after Prussian blue staining; we achieved a linear correlation between the logarithm of the LH concentration and the average integrated transmission values. Crossreacting and nonspecific interfering blood serum compounds were grossly removed by means of ion-exchange chromatography on CM-Sephadex-C-50 columns yielding about 77% of LH. Without chromatography there would have been increasing LH recovery with increasing LH concentrations. Also the presence of FSH either in unextracted serum or after apposition, resulted in LH overestimation due to dose related changes in the slope of the standard curve. Dilution curves of chromatographed bovine blood serum and of purified LH, hCG and PMSG were parallel. The recovery of added LH in the assay averaged 103%. The linear LH dose response curve was maximally ranging from 10 fg-10 ng purified bovine pituitary LH standard. The intra assay variation resulted as 18.8 +/- 6.9%, the interassay variation as 4.6 +/- 4.7% (x(-) +/- SD). The LH pattern in purified bovine serum during the oestrous cycle and after administration of GnRH shows a close correlation whether measured by means of radioimmunoassay or cytohistochemical assay. The surge RIA-LH values are similar to the cytohistochemically measured ones, but the basal cytohistochemical LH levels are consistently lower (35-430 pg/ml compared to 0.8-2.1 ng/ml by RIA). These results give no indication for a different biological and immunological LH activity in bovine blood.

Animals↗