Lack of effect of melatonin on sexual maturation in female rats

Badawi, H.; Wilkinson, Michael

doi:10.1530/jrf.0.0830273

Cited by 11 publications

(5 citation statements)

References 19 publications

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Section: Mammalsmentioning

confidence: 87%

“…Rivest et al (1985) injected melatonin into female Wi star rats from Swiss colonies and found a 10-day delay in vaginal opening. The effect was not replicated in another study in which rats from North American colonies were used (Badawi and Wilkinson, 1988).Rats and other nocturnal mammals appear to be much more sensitive to light intensity than humans. Fluorescent light below 5 lux intensity resulted in a 50% reduction in SNAT activity in rats (Minneman et al, 1974).…”

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confidence: 91%

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Seasonal Patterns of Melatonin, Cortisol, and Progesterone Secretion in Female Lambs Raised Beneath a 500-kV Transmission Line

Lee¹

2000

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There is ongoing controversy about the possibility of adverse biological effects from environmental exposures to electric and magnetic fields. These fields are produced by all electrical equipment and appliances including electrical transmission lines. The objective of this environmental science study was to investigate the possible effects of a high voltage transmission line on domestic sheep (Ovis aries L,), a species that can often be found near such lines.The study was primarily designed to determine whether a specific effect of electric and magnetic fields found in laboratory animals also occurs in livestock under natural environmental conditions. The effect is the ability of fields, at levels found in the environment, to significantly depress the normally high nocturnal concentrations of the pineal hormone melatonin.Melatonin mediates the reproductive response to changes in photoperiod in seasonal breeders such as sheep. Factors which modify the production of nocturnal melatonin in sheep can have important effects on the timing of seasonal reproduction including the onset of puberty in this species.Ten female Suffolk lambs were penned for 10 months directly beneath a 500-kV transmission line near Estacada, Oregon. Ten other lambs of the same type were penned in a control area away from the transmission line where electric and magnetic fields were at ambient levels.Serum melatonin was analyzed by radioimmunoassay (RIA) from 6618 blood samples collected at 0.5 to 3-hour intervals over eight 48-hour periods. Serum progesterone was analyzed by RIA from blood samples 3 collected twice weekly beginning when the lambs were 23 weeks old. This hormone was used to measure the onset of puberty.Serum cortisol was also assayed by RIA from the blood samples collected during the 48-hour samples. This was done to assess whether exposure to the transmission line produced stress in the growing lambs.Other supplemental biological data collected included body weight gain, wool growth, and behavior.1 extensive study was conducted by engineers from the Bonneville Power Administration (BPA) to measure electric and magnetic fields and noise to which the lambs were exposed. Tnis was accomplished by installing permanent monitors near both the control and line pens.Results showed that lambs in both the control and line groups had the typical pattern of melatonin secretion consisting of low daytime and high nighttime serum concentrations. There were no statistically significant differences between groups in melatonin levels, or in the phase or duration of the nighttime melatonin elevation. Age at puberty and number of reproductive cycles also did not differ between groups.Serum cortisol showed a circadian rhythm with highest concentrations during the day. Cortisol concentrations also seemed to reflect effects of known stressors on livestock, e.g., weaning, introduction to new housing, and vehicle transport. There were, however, no differences in cortisol concentrations between groups.Statistical analyses on other biological parameter...

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Section: Mammalsmentioning

confidence: 87%

mentioning

confidence: 91%

Seasonal Patterns of Melatonin, Cortisol, and Progesterone Secretion in Female Lambs Raised Beneath a 500-kV Transmission Line

Lee¹

2000

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“…In contrast, some researchers (Badawi and Wilkinson, 1988) have declared that daily injections of MT, at the appropriate time, in appropriate dose under controlled temperature and lighting arrangements failed to delay puberty, irrespective of the colony of rats used. As a matter of fact, Badawi and Wilkinson (1988) found that the vaginal opening was significantly advanced by 1.5 days. In our experiment, 5-day-old rats treated with MT for 10,15, and 20 days all had a VOD earlier than their corresponding control rats with values ranging from 2.67-7 days, which are all statistically significant.…”

Section: Discussionmentioning

confidence: 98%

Effect of exogenous melatonin on the onset of puberty in female albino rats

Batmanabane

Ramesh

1996

Anat. Rec.

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Background The influence of melatonin (MT) on the onset of puberty has attracted many researchers leading to many contradictory claims. Although some researchers believe that exogenous MT delays the onset of puberty in female juvenile rats, others dispute this finding. We explored the effects of exogenous MT, administered for different periods of time, on very young pups. Methods Groups of 5‐ and 10‐day‐old rat pups were given daily 100 μg of MT subcutaneously for 10, 15, and 20 days at 1500 hours. On the vaginal opening day (VOD), rats were sacrificed for collection of ovary and thymus. Besides measuring ovarian and thymus weights, Graafian follicular ratio and thymic corticomedullary ratio were computed. Results MT caused an advancement of VOD in 5‐day‐old pups but delayed it in 10‐day‐old ones. Other parameters studied revealed an exciting correlation with this reversed trend in VOD. In the 5‐day‐old groups, the ovaries and thymuses showed an increase in weights, but the 10‐day‐old groups recorded a fall. Follicular and thymic corticomedullary ratios also displayed corresponding increases and decreases. Conclusions MT administered to younger pups (5 day old) causes an earlier VOD probably due to an ovarian stromal inhibition. In slightly older pups (10 days old), where most secretory mechanisms are progressing from an immature to an adult type, perhaps exogenous MT depresses the developing and sensitive thymus‐hypothalamus‐pituitary‐gonadal axis (THPGA) and causes a delay in VOD. © 1996 Wiley‐Liss, Inc.

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“…The low levels of mela tonin at the time of sexual maturation in the female rabbit 100-120 days of age [9,10,22] also provides similar presumptive evidence. The question arises as to whether the pre sumptive high pineal gland activity on days 72-91 plays a role in inducing puberty, and would be contradictory to previous evidence indicating that melatonin delays puberty in the rat [23][24][25][26], On the other hand, more recent data failed to show an effect of mela tonin on puberty in the female rat [25] but increased LH pulse amplitude in women [27], High melatonin levels have been associated with infertility [28,29]. If high melatonin causes infertility by inducing a sustained in crease in LH pulse amplitude without appro priate negative feedback from the gonads, one would expect a delay in puberty.…”

Section: Discussionmentioning

confidence: 99%

Light-Related Melatonin Changes in Pituitary Response to Gonadotropin-Releasing Hormone during Sexual Development in the Female Rabbit

Younglai¹,

Todoroff²,

Foster³

et al. 1992

Biological Signals

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Melatonin levels in the blood of female rabbits were determined from the time of weaning to adulthood in a longitudinal study. Blood samples were taken at 3 h after light onset and 1 h after dark onset and plasma was analysed for melatonin, LH and FSH by radioimmunoassay procedures. The animals were sacrificed on days 25, 32, 39, 51, 72, 91 and 120 days of life and pituitaries removed for in vitro incubation of slices to determine their response to GnRH. Circulating melatonin levels were significantly higher in the dark compared to the light phase and peaked on days 72 and 91 when gonadotropin levels were at a nadir. Melatonin levels on day 120 were lower than those on any other day examined. Basal secretion of LH and FSH by pituitary slices in vitro increased several-fold from day 25 of age to days 51–91 and then decreased by day 120. The pituitary gonadotropin responsiveness to GnRH in vitro was also different: while LH generally increased, FSH accumulation remained constant after GnRH stimulation. These data suggest that the female rabbit pituitary undergoes changes in sensitivity to GnRH during sexual maturation and that the pineal gland may play a role in this process.

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Lack of effect of melatonin on sexual maturation in female rats

Cited by 11 publications

References 19 publications

Seasonal Patterns of Melatonin, Cortisol, and Progesterone Secretion in Female Lambs Raised Beneath a 500-kV Transmission Line

Seasonal Patterns of Melatonin, Cortisol, and Progesterone Secretion in Female Lambs Raised Beneath a 500-kV Transmission Line

Effect of exogenous melatonin on the onset of puberty in female albino rats

Light-Related Melatonin Changes in Pituitary Response to Gonadotropin-Releasing Hormone during Sexual Development in the Female Rabbit

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