Possible prolactin-mediated effects of melatonin on gonadotropin secretion in the rat (original) (raw)
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Acta neurobiologiae experimentalis, 2001
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 r...
The Journal of Steroid Biochemistry and Molecular Biology, 2000
The purpose of this study was to investigate the eects of prenatal melatonin administration on the sensitivity of the androgens negative feedback eect on gonadotropin and prolactin secretion in male ospring. Male ospring of control (control-ospring) and melatonin treated (MEL-treated) (150 mg/100 g BW) mother rats during pregnancy (MEL-ospring), at infantile, prepubertal, and pubertal periods were studied. LH secretion in response to testosterone propionate (TP) in controlospring showed the classical negative feedback eect at all ages studied. In MEL-ospring a negative response after TP was also observed in all ages studied although the magnitude of this response was altered in this group as compared to controls. FSH values were signi®cantly lower at most ages and time points studied in MEL-ospring than in control-ospring. FSH secretion in MEL-ospring showed a delayed negative feedback action of TP injection as compared to control-ospring. This response was observed at 21 days of age in control-ospring and delayed until day 30 of life in MEL-ospring. Parallely it remain at later age in MEL-ospring than in control-ospring. Prolactin secretion in control-ospring showed increased values after TP injections from infantile to pubertal periods. This increase was blunted in MEL-ospring at 17 and 35 days of age showing signi®cantly reduced p`0X01; p`0X05 plasma prolactin levels. During pubertal period a prolactin positive response to TP administration was observed in MEL-ospring but with signi®cantly lower magnitude than in control-ospring. These results indicate that prenatal melatonin exposure induced changes in the sensitivity of gonadotropin and prolactin feedback response to testosterone, indicating a delayed sexual maturation of the neuroendocrine-reproductive axis in male ospring.
Reproduction, 1986
Juvenile hamsters were injected daily with melatonin and some were also given transplants of 2 pituitaries under the kidney capsule. Weights of the testes and the accessory reproductive glands were reduced after 8 and after 12 weeks of melatonin treatment, but remained unaltered in animals treated with ectopic pituitary transplants. Levels of testicular LH/hCG receptors were significantly reduced by daily melatonin injections for 8 and 12 weeks. The presence of pituitary transplants in melatonin\x=req-\ injected hamsters prevented these reductions, and increased LH/hCG receptors above control levels. These changes in testicular LH/hCG receptors were closely related to alterations in serum prolactin concentration induced by melatonin and pituitary transplants. After 8, but not after 12 weeks of treatment, testicular prolactin receptor levels were reduced by melatonin and maintained by the presence of pituitary transplants. We conclude that: (a) juvenile male hamsters become sensitive to the effects of daily melatonin injections when they reach maturity; (b) daily melatonin injections can reduce the levels of testicular LH/hCG and prolactin receptors; and (c) the effects of melatonin on LH/hCG and prolactin receptors are probably due to suppression of endogenous prolactin release.
Annales de Biologie Animale Biochimie Biophysique, 1979
Adult female Syrian hamsters (64-82 g) were ovariectomized and thereafter maintained under light : dark cycles of 14 : 10. After 56 days of treatment the animals were killed and pituitary and plasma levels of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) were measured by radioimmunoassay. Ovariectomy caused marked rises in both the content and concentration of LH and FSH within the pituitary gland while pituitary PRL levels fell. Plasma levels of LH and FSH also rose while PRL titers remained unchanged. The daily afternoon injection of melatonin (25 ¡ L g subcutaneously) further increased the accumulation of LH and FSH within the pituitary. These responses to daily melatonin injections were prevented if animals additionally received biweekly subcutaneous melatonin-beeswax pellets (1 mg melatonin in 24 mg wax) which presumably released melatonin continually.
Effect of melatonin in vivo upon FSH and LH release from hamster pituitary glands
Molecular and Cellular Endocrinology, 1986
The effect of chronic daily afternoon injections of melatonin upon basal and melatonin-modulated release of FSH and LH was investigated in superfused hamster anterior pituitary glands. The basal release rate of both FSH and LH began to decline following the beginning of melatonin injections, and reached a nadir after six weeks. Basal release rate of FSH and LH then began to spontaneously increase and reached a plateau at 13 weeks of injections. The inhibition by melatonin upon FSH and LH release in vitro gradually declined during the period of melatonin injections. After six weeks of melatonin injections the release rate of FSH was no longer suppressed by melatonin superfusion, while the release rate of LH became refractory to melatonin suppression in vitro after nine weeks of melatonin injections. These results demonstrate a change in the release rates of both basal and melatonin-inhibited gonadotropin release during melatonin-induced testicular regression and recrudescence in hamsters.
An Overview of Effects on Reproductive Physiology of Melatonin
Melatonin - Recent Updates [Working Title]
Melatonin is a neurotransmitter released from the pineal gland. The presence of receptor sites in the hypothalamus, pituitary gland, ovaries, and testicles and secretion of pituitary hormones (FSH and LH) are some of the effects of this hormone on reproduction. In addition to its systemic effect, it also showed an effect on ovarian physiology with the detection of high levels in the follicular fluid and the presence of melatonin receptors in the ovarian cells. In addition, it has been determined that melatonin affects follicular growth, oocyte maturation, ovulation, and luteal function. It has been stated that the effects of melatonin on the male reproductive system are indirectly effective through the gonads and indirectly by affecting the hormones. Again, some studies have expressed that melatonin has strong antioxidant properties and affects reproductive physiology due to this effect. This section discusses the effect of melatonin on male and female reproductive physiology.
European Journal of Histochemistry, 2009
The gonadotropes, LH and FSH cells, were immunohistochemically identified in the pituitary pars distalis of the adult male viscacha (Lagostomus maximus maximus) using specific antibodies against hLH‚ and hFSH‚ with the streptavidinbiotin-peroxidase complex. The distribution, size and percentage immunopositive area of these cells were analyzed by image analysis in viscachas captured during the annual reproductive cycle and after the chronic administration of melatonin. The LH‚ and FSHβ cells showed seasonal changes in the distribution, size and percentage immunopositive area. The LHβ cells were found widely distributed throughout the pars distalis during the reproductive period, and they were found in the ventro-medial region in the pars distalis during the gonadal regression and gonadal recovery periods. The LHβ cells reached the largest size and immunopositive area during the reproductive period and the smallest size and immunopositive area during the gonadal regression period. The FSHβ cells were found in the ventro-medial region during reproductive and gonadal regression periods. The FSHβ cells were found widely distributed throughout the pars distalis during the gonadal recovery period when they showed the maximum percentage immunopositive area. A decrease in the size of LH‚ and FSHβ cells was observed after the chronic administration of melatonin. Moreover, it produces a decrease in the immunopositive area occupied by the LH‚ cells but not in the immunopositive area occupied by the FSHβ cells. Our results show great activity of LHβ and FSHβ cells in different moments of the annual reproductive cycle demonstrating that these cells are not secrete in parallel. Moreover, melatonin acts differentially on the activity of the gonadotrope cells.
Effects of melatonin and prolactin in reproduction: review of literature
Revista da Associação Médica Brasileira, 2015
Summary The pineal gland is responsible for producing a hormone called melatonin (MEL), and is accepted as the gland that regulates reproduction in mammals. Prolactin (PRL) also exhibits reproductive activity in animals in response to photoperiod. It is known that the concentrations of PRL are high in the summer and reduced during winter, the opposite of what is seen with melatonin in these seasons. In placental mammals, both prolactin and melatonin affect implantation, which is considered a critical point of pregnancy, since a successful pregnancy requires the development of a synchronous interaction between the endometrium and blastocyst for placental development. It is also known that PRL levels during pregnancy are essential for the maintenance of pregnancy, because this hormone induces the corpus luteum to produce progesterone, in addition to stimulating blastocyst implantation to maintain pregnancy and form the placenta. However, melatonin levels in plasma have also been shown...
Melatonin and Sex Hormone Interrelationships - A Review
Journal of Pediatric Endocrinology and Metabolism, 1999
Melatonin, the main hormone secreted by the pineal gland at night, plays a major role in regulating reproductive physiology in seasonal breeders and influences the age of sexual maturation in laboratory rodents. In humans these relationships are less clear. Evidence supporting a melatonin-reproductive hormone relationship relies on findings of abnormal melatonin secretion in disorders of the reproductive system and on pathologies of the pineal gland which are associated with clinical abnormalities of the reproductive hormones. Normal melatonin rhythms are closely related to those of the reproductive hormones during infancy and reciprocally correlated during puberty. The demonstration of melatonin receptors in the brain and in reproductive organs, together with the localization of sex hormone receptors in the pineal gland, further strengthen these relationships. However, it is not yet clear that these correlations are functionally related, as data on the antigonadal effects of exogenous melatonin on the reproductive hormones are not conclusively established.
Journal of Pineal Research, 1984
The combination of pituitary grafts and daily injections of gonadotrophin-releasing hormone (GnRH) completely prevents gonadal atrophy in blind (BL) and melatonin (Mel)-treated male hamsters. In order to avoid potential problems associated with the use of pituitary grafts and further define the interactions between prolactin (PRL) and GnRH in preventing reproductive regression, we injected various doses of each hormone either alone or in combination into BL or Mel-treated male hamsters. In another experiment, BL hamsters received either weekly beeswax implants of estradiol benzoate (EB) (1 mg) alone or EB implants in combination with daily injections of GnRH (2 micrograms). In each experiment the hamsters were BL and/or treated with hormones for 10 wk. Either GnRH (8 micrograms) or PRL (5 micrograms) per d partially prevented gonadal atrophy in BL hamsters. However, increasing doses of GnRH plus PRL were more effective than either hormone alone in preventing gonadal atrophy. The combined effect of these hormones was greater than the algebraic sum of their individual effects. Injections of either GnRH or PRL alone resulted in a significant maintenance of gonadal and accessory organ size in Mel-treated animals. The combination of GnRH and PRL resulted in virtually complete maintenance of testicular weight while the accessory sex organs remained atrophic. The combined effect of these hormones was equivalent to the algebraic sum of their individual effects. The treatment of BL animals with EB implants with or without GnRH did not prevent reproductive regression in spite of elevated serum PRL levels. In conclusion, the effects of GnRH and PRL were synergistic in BL hamsters and additive in Mel-treated animals. The data suggest that there is a differential responsiveness of BL v. Mel-treated hamsters to the individual as well as the combined actions of GnRH and PRL.