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1

Daily GnRH and LH secretion in ewes is not modified by exogenous melatonin during seasonal anestrus

100%

Romanowicz K. , Misztal T. , Gajewska A. , Barcikowski B.

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nr 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.

2

Melatonin action on thyroid activity in the soft-shelled turtle, Lissemys punctata punctata

100%

Sarkar S. , Sarkar N. K. , Bhattacharyya S. , Das P.

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tom 45

109-112

EN

Adult female turtles (Lissemys punctata punctata) were treated with pineal indoleamine melatonin (100 mug/100 g) or the antithyroid agent, methylthiouracil (100 mug/100 g) or melatonin together with methylthiouracil (100 mug of each drug/100 g) for 12 days. Melatonin alone inhibited thyroid activity as evidenced by reductions in the gland weight, follicular epithelial cell height, thyroid peroxidase, and plasma thyroxine levels. Methylthiouracil caused hyperplasia of the gland, although it inhibited thyroid activity and reduced thyroid peroxidase and plasma thyroxine levels. Melatonin together with methylthiouracil produced changes similar to those obtained with melatonin alone. The results indicate that melatonin probably exerts inhibitory effects influences on both thyrotropin release from the pituitary and the activity of the thyroid itself in turtles.

3

Changes in selected blood metabolites associated with melatonin administration in dairy goats

100%

Darul K. , Kruczynska H.

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tom 52

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nr 3-4

239-241

EN

In order to examine the effect of exogenous melatonin on selected blood indices, dairy goats were given pineal gland hormone at a dose of 0.1 mg/kg body weight. Next, one and four hours after the melatonin had been administered, blood samples were collected from the goats in the control and treated groups in order to determine the levels of glucose, total cholesterol, triacyloglycerides, free fatty acids, as well as alanine and aspartate aminotransferase. The pineal gland hormone caused a significant increase in the levels of glucose, total cholesterol, triacyloglycerides and the activity of alanine aminotransferase. After melatonin administration a significant decrease in the FFA:TAG and FFA:Cholesterol blood ratios was observed. Moreover, no changes in the free fatty acid concentrations and the activity of aspartate aminotransferase were observed.

4

On light as an alerting stimulus at night

88%

Figueiro M. G. , Bullough J. D. , Bierman A. , Fay C. R. , Rea M. S.

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2007

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tom 67

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nr 2

171-178

EN

Light exposure at night increases alertness; however, it is not clear if light affects nocturnal alertness in the same way that it affects measures of circadian regulation. The purpose of this study was to determine if a previously established functional relationship between light and nocturnal melatonin suppression was the same as that relating light exposure and nocturnal alertness. Four levels of narrow-band blue light at the cornea were presented during nighttime sessions. The ratio of electroencephalographic alpha power density with eyes closed to eyes open (alpha attenuation coefficient, AAC) and the Norris mood scale were used. The AAC and ratings of alertness increased monotonically with irradiance and were highly correlated. Both measures of alertness were highly correlated with model predictions of nocturnal melatonin suppression for the same circadian light stimulus, consistent with the inference that the suprachiasmatic nuclei play an important role in nocturnal alertness as well as circadian regulation.

5

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

88%

Misztal T. , Romanowicz K. , Barcikowski B.

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nr 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.

6

Time and reproductive phase-dependent effects of exogenous melatonin on the pineal gland and ovary of a nocturnal bird, the indian spotted owlet, Athene brama

75%

Guchhait P. , Haldar C.

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nr 3-4

91-96

EN

In a tropical nocturnal bird, the Indian spotted owlet, Athene brama, the intraperitonial injection of an identical amount (20mg/ 100 g b. wt/ day) of exogenous melatonin (MEL) for 15 consecutive days increased the pineal weight and plasma MEL level in sexually active birds while it decreased them in inactive birds more potently when injected in the evening (18.30-19.30 h) rather than the morning (0500-0600 h). On the other hand, more efficiently than the morning hour treatment, the evening hour MEL injection decreased the ovary weight and plasma estradiol and progesterone levels both in sexually active and inactive birds, but more potently in active than inactive birds. Thus, the exogenous MEL showed the time and reproductive phase dependent effects on the pineal gland and the ovary of this nocturnal bird.

7

In vitro pituitary prolactin, growth hormone and follicle stimulating hormone secretion during sexual maturation of female rats primed with melatonin

75%

Diaz_ R. E. , Fernandez_ A. C. , Castrillon P. O. , Esquifino_ P. A. I. , Diaz_ L. B.

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nr 1

27-33

EN

The influence of in vivo melatonin administration on in vitro pituitary follicle stimulating hormone (FSH), growth hormone (GH) and prolactin secretion, as well as the possible influence of dopamine (DA) were evaluated in prepubertal (31-day-old), pubertal (33-day-old) and adult female rats at diestrus phase of the sexual cycle. The in vitro pituitary hormone secretions were evaluated at basal rate for the first hour of incubation only, in Krebs Ringer phosphate (KRP) (I1) and after a second hour of incubation with KRP (I2) or with KRP+DA (I2 plus DA). I1PRL secretion was significantly higher in 33-day-old control and melatonin treated (MEL) rats as compared to I2 periods. However, in 31-day-old rats I1 secretion was higher than in the I2 or I2+DA periods, in MEL rats. In vitro GH secretion was significantly higher at I1 than during I2 periods in the control 31- and 33-day-old groups, but not in MEL rats. The only significant effect of DA was the elevation of GH in prepubertal MEL rats. In vitro FSH release was increased by melatonin in 31-and 33-day-old female rats. No differences in PRL, GH and FSH secretion were found in adult rats. In conclusion, the results show that melatonin effects upon in vitro pituitary gland activity are reproductive-stage-dependent modifying the secretory capacity of the lactotrop, gonadotrop and somatotrop during prepubertal and pubertal ages but not in adult rats studied at a quiescent phase of the sexual cycle.

8

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

75%

Misztal T. , Romanowicz K.

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tom 65

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nr 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.