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1
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Effective stimulation of daily LH secretion by the combined treatment with melatonin and naloxone in luteal-phase ewes

100%
Misztal T., Romanowicz K.
Acta Neurobiologiae Experimentalis
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2005
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vol. 65
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issue 1
1-9
EN
This study was designed to test the hypothesis that melatonin would intensify daily LH release after central blockade of the opiate receptors in sexually active ewes. The intracerebroventricular infusions of vehicle (control), melatonin, naloxone and melatonin in combination with naloxone were made in ewes in the luteal phase of the estrous cycle, from 2:00 P.M. to 5:00 P.M. Blood samples were collected from 11:00 A.M. to 8:00 P.M. at 10-min intervals. The mean plasma LH concentrations were measured before, during and after the infusions. The frequency and amplitude of LH pulses were determined during the whole experimental period. The LH concentrations recorded during melatonin or naloxone infusions were significantly higher than the concomitant concentration in vehicle-infused animals. The mean LH pulse amplitude in melatonin- and naloxone-treated ewes was also significantly higher than in controls. The LH concentration measured during the combined infusion of melatonin and naloxone was significantly higher than that during vehicle infusion. The LH concentration recorded in turn after the treatment was significantly higher than the concomitant concentrations in vehicle-, melatonin- and naloxone-infused animals. The mean LH pulse amplitude in this group was significantly higher than in the vehicle-infused group. These results indicate that blockade of the opiate receptors within the CNS facilitated effective stimulation of daily LH secretion by exogenous melatonin. In conclusion, a relationship between melatonin and endogenous opioid peptides may be crucial in enabling melatonin to exhibit stimulatory action on LH secretion during the luteal phase of the estrous cycle in ewes.
2
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Effects of melatonin infused into the III ventricle on prolactin, beta-endorphin and luteotropin secretion in ewes during the different stages of the reproductive cycle

81%
Misztal T., Romanowicz K., Barcikowski B.
Acta Neurobiologiae Experimentalis
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1996
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vol. 56
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issue 3
769-778
EN
Secretion of all the pituitary hormones undergoes marked circadian and seasonal changes.The rhythmicity of these changes is controled by the circadian pacemaker system and the pineal gland transmitting daylength informatoin to the neuroendocrine axis via the secretion of melatonin.This article presents data on the effects of the short-term melatonin administratoin into the third brain ventricle on prolactin, beta-endorphin and luteotropin secretion in ewes kept under the increasing and decreasing daylenght conditions.Additional emphasis is given to dopamine and LHRH release in the madiobasal hypothalmus under the malatonin treatment by the push-pull method.The long-term and short-term actions of melatonin on the hormonal status in ewes is also discussed.
3
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Thyroid hormones in the cerebrospinal fluid of the third ventricle of adult female sheep during different periods of reproductive activity

81%
Skipor J., Misztal T., Szczepkowska A.
Polish Journal of Veterinary Sciences
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2010
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issue 4
4
Content available remote

Central estrogen-like effect of genistein on growth hormone secretion in the ewe

81%
Misztal T., Wankowska M., Gorski K., Romanowicz K.
Acta Neurobiologiae Experimentalis
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2007
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vol. 67
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issue 4
411-419
EN
The present study tested a hypothesis, whether plant-derived genistein influences the secretion of growth hormone (GH) in ewes, acting directly within the central nervous system (CNS). Starting six weeks after ovariectomy, ewes were infused intracerebroventricularly with genistein (n = 5) or 17beta-estradiol (n = 5), both in a total dose of 40 microg/400 microl/4 h, or with a vehicle (control, n = 5). All infusions were performed from 10:00 AM to 2:00 PM and blood samples were collected from 8:00 AM to 8:00 PM at 10-min intervals. Five genistein- and three vehicle-infused ewes were slaughtered the following morning. The plasma GH concentration was assayed by the radioimmunoassay method, and immunoreactivity of GH in the adenohypophysis was determined by immunohistochemistry. In genistein-infused ewes, mean plasma GH concentration was significantly higher during the whole period of infusion than the concomitant concentration in vehicle-infused ewes. However, examining data within group, GH secretion rose gradually, reaching a significant value during the second phase of genistein infusion. In 17beta-estradiol-infused animals, a significant increase in GH concentration was noted during the first two hours of the infusion, in comparison with vehicle-infused and also in comparison with genistein-infused ewes. Although a gradual increase in basic GH secretion continued in all treated groups during the afternoon and evening, mean plasma GH concentrations in genistein- and 17beta-estradiol-infused ewes were still significantly higher than in the vehicle-infused. The percentage of GH-positive cells in the adenohypophysis and the density of immunoreactive material in these cells decreased significantly in genistein-infused ewes, compared to the control, indicating diminished hormone storage. In conclusion, genistein as 17beta-estradiol, is an effective stimulator of GH secretion in ewes and may exert its effect at the level of the CNS.
5
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Daily GnRH and LH secretion in ewes is not modified by exogenous melatonin during seasonal anestrus

81%
Romanowicz K., Misztal T., Gajewska A., Barcikowski B.
Acta Neurobiologiae Experimentalis
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2001
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vol. 61
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issue 4
289-297
EN
The effect of central, short-term melatonin administration on daily GnRH and LH secretion was studied in ewes during seasonal anestrus. Melatonin, in a total dose of 32 g and the vehicle were perfused for 4 hours into the mediobasal hypothalamus/median eminence (MBH/ME). The mean GnRH concentration during perfusion with melatonin decreased significantly (P0.05), as compared to the concentration during the preceding perfusion with the vehicle only. This change resulted from high variations in GnRH concentration noted during the initial phase of perfusion rather than from an action of melatonin. Melatonin perfused into the MBH/ME did not significantly affect LH secretion. A higher dose of melatonin and vehicle were also infused intracerebroventricularly (icv.) in either intact (300 g for 3 hours) or ovariectomized (OVX) ewes (400 g for 4 hours, 100 g/100 l/h). In the intact animals, melatonin did not significantly affect LH secretion. Interestingly, melatonin significantly decreased (P0.05) the number of LH peaks in OVX ewes. These results demonstrate that melatonin delivered for a few hours directly into the central nervous system did not affect either daily hypothalamic GnRH release or pituitary LH secretion in intact ewes during seasonal anestrus, but did modify pulsatile LH secretion in ewes deprived of the negative feedback of estradiol.
6
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Differential endocrine response in rams to intracerebroventricular infusion of genistein

81%
Misztal T., Gorski K., Romanowicz K.
Acta Neurobiologiae Experimentalis
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2008
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vol. 68
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issue 1
43-50
EN
The intracerebroventricular infusions of genistein (total 40 ?g) were made in male sheep (November) to test its influence on melatonin, growth hormone (GH) and luteinizing hormone (LH) secretion. The analysis of the results encompassed 3 similar periods: before the infusion (afternoon hours), the first (evening hours), and the second (night hours) halves of the treatment. The night plasma concentration of melatonin in genistein-infused rams was significantly lower than that noted during the respective period in vehicle-infused rams. Plasma GH concentration increased significantly in both vehicle- and genistein-infused rams during the night hours, as compared with the concentrations noted during the afternoon and evening, however, genistein significantly stimulated the amplitude of GH pulses in these latter. The LH concentration was significantly lower during the second part of genistein treatment, than in vehicle-infused rams. The frequency and amplitude of LH pulses clearly tended to decrease following genistein infusion. In conclusion, genistein, acting at the central nervous system level in sexually active rams is able to reduce the secretion of melatonin and LH and has also a slight stimulatory effect on the amplitude of GH pulses.
7
Content available remote

Effect of stress on the expression of GnRH and GnRH receptor (GnRH-R) genes in the preoptic area-hypothalamus and GnRH-R gene in the stalk/median eminence and anterior pituitary gland in ewes during follicular phase of the estrous cycle

61%
Ciechanowska M., Lapot M., Malewski T., Misztal T., Mateusiak K., Przekop F.
Acta Neurobiologiae Experimentalis
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2007
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vol. 67
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issue 1
1-12
EN
The RT-PCR (reverse transcription polymerase chain reaction) technique was used to analyze GnRH mRNA and GnRH-R mRNA in the preoptic area, anterior and ventromedial hypothalamus, and GnRH-R mRNA in the stalk/median eminence and anterior pituitary gland of follicular ewes subjected to short (3 h during one day) or prolonged (5 h daily during four consecutive days) footshock stimulation. To analyze relationship between expression of GnRH and GnRH-R genes with LH secretion the blood samples were collected at 10 min intervals to determine LH levels in control and stressed animals. The concentration of GnRH mRNA increased significantly in the preoptic area, anterior and ventromedial hypothalamus of ewes subjected to short stress. The prolonged stressful stimuli significantly decreased GnRH mRNA levels in all analyzed structures. In short stressed ewes the significant augmentation of mRNA encoding GnRH-R was detected in the preoptic area, entire hypothalamus, stalk/median eminence and anterior pituitary gland. The GnRH-R mRNA was significantly reduced in all tested structures of animals subjected to prolonged footshocking except for the preoptic area, where GnRH-R mRNA did not differ from control values. The changes in GnRH mRNA and GnRH-R mRNA levels under short or prolonged stress were associated with an increase or decrease of LH concentration in blood plasma, suggesting the existence of a direct relationship between GnRH mRNA and GnRH-R mRNA expression with LH secretion. The results indicate that the expression of both GnRH gene and GnRH-R gene, as well as LH secretion in ewes during the follicular phase of the estrous cycle, are dependent upon the kind of stress.
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