Melatonin can induce year-round ovarian cyclicity in red deer (Cervus elaphus)

Adam, Carole; Moir, C E; Shiach, P

doi:10.1530/jrf.0.0870401

Cited by 15 publications

(7 citation statements)

References 16 publications

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“…The ability of melatonin implants, inserted at the spring equinox, to prevent seasonal anoestrus provides further support for the contention that the duration of the daily photoperiod is the primary determinant of this reproductive seasonality. Melatonin implants, inserted at or soon after the spring equinox, prevented the occurrence of seasonal anoestrus and maintained continuous oestrous cycles for the duration of the study, just as daily oral administration of melatonin at 15:00 h throughout the summer does in red deer hinds (Adam et al, 1989). This finding is in contrast to the situation in sheep, in which prolonged maintenance of a short-day photoperiod after the winter solstice, or its simulation by melatonin implants, fails to prolong the breeding season significantly (Malpaux et al, 1988).…”

Section: Discussionmentioning

confidence: 99%

Reproductive seasonality in domestic sows kept outdoors without boars

Bassett¹,

Cj²,

Sharpe³

2001

Reproduction

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Plasma progesterone, LH and prolactin concentrations were measured twice a week in mature sows kept outdoors without boars in two experiments to examine whether perception of daylength change underlies seasonal infertility in domestic pigs. In Expt 1, melatonin implants inserted on 12 April or 22 May to block perception of the increasing daylength did not affect the oestrous cycle significantly, since only two untreated control sows became seasonally anoestrous. In Expt 2, all control sows became anoestrous for 131 +/- 42.5 days (n = 11). Melatonin implants inserted at the spring equinox (n = 9) prevented seasonal anoestrus (P < 0.001), but timed daily oral melatonin administration was less effective (P < 0.05): 5 of 11 sows became anoestrous for 132 +/- 45.6 days. In both experiments, there were significant low-amplitude seasonal rhythms in mean plasma prolactin and LH concentrations. Prolactin reached maximum concentrations 2-4 weeks before the summer solstice, whereas LH reached a nadir 4-6 weeks after the summer solstice. Neither anoestrus nor melatonin administration altered these patterns consistently. Endogenous plasma melatonin was higher (P < 0.001) during darkness (12.5 ng l(-1)) than during daytime (8.9 ng l(-1)) in untreated sows, but only clearly so during spring and summer. Melatonin implants increased mean daily plasma melatonin to 146 ng l(-1), whereas melatonin fed at 15:00 h increased values to 40-60 ng l(-1) 2-4 h after administration, but daytime concentrations were unchanged. Melatonin administration, despite decreasing seasonal anoestrus, did not prevent the seasonal increase in plasma prolactin and had no significant effect on plasma LH; therefore, its role in regulating seasonal changes in the reproduction of domestic sows remains uncertain.

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Section: Discussionmentioning

confidence: 99%

Reproductive seasonality in domestic sows kept outdoors without boars

Bassett¹,

Cj²,

Sharpe³

2001

Reproduction

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“…These results show clearly that oral application of melatonin to extend the period each day when plasma melatonin is increased, thus mimicking the natural endogenous diurnal rhythm typical of short days, overcomes the inhibition of puberty, but that the provision of a constant-release implant does not. In this, domestic pigs differ from sheep and deer, in which both implants and oral melatonin can stimulate reproductive activity under inhibitory photoperiods (Kennaway et al, 1982;Lincoln & Ebling, 1985;Adam & Atkinson, 1984;English et al, 1986;Adam et al, 1989). We have previously shown that constant-release melatonin implants given by the same regimen as used in Expt 1 provide a constant, high plasma melatonin concentration above which a diurnal rhythm cannot be detected (Paterson et al, 1992).…”

Section: Discussionmentioning

confidence: 99%

“…In sheep (Kennaway et al, 1982;Lincoln & Ebling, 1985;English et al, 1986), deer (Adam & Atkinson, 1984;Adam et al, 1989;Fisher et al, 1989) and goats (McGregor et al, 1989) inhibition of reproductive activity by long days can be overcome by the administration of exogenous melato¬ nin, given either orally or by slow-release implant. We have already demonstrated that the seasonal inhibition of attainment of puberty in domestic gilts can be prevented by applying a short-day regimen (Paterson & Pearce, 1990), but such methods may be difficult to use in combating seasonal reproductive dysfunctions at the practical level.…”

Section: Introductionmentioning

confidence: 99%

Seasonal inhibition of puberty in domestic gilts is overcome by melatonin administered orally, but not by implant

Paterson

Maxwell²,

Foldes³

1992

Reproduction

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The ability of exogenous melatonin, applied either orally or by implant, to overcome the seasonal inhibition of puberty in domestic gilts was tested in two experiments. In Expt 1, 24 gilts received two melatonin implants at 126 days of age and again at 161 days and 196 days, while 24 gilts acted as controls. All gilts were slaughtered at a mean age of 223 days. Blood samples were collected by venepuncture from eight gilts in each treatment at 126, 144 and 178 days of age and the plasma was assayed for melatonin concentration by direct radioimmunoassay. In Expt 2A, four gilts (125 days of age) were fed either 0, 1, 2 or 4 mg of melatonin at 14:00 h on each of four consecutive days. Blood samples for melatonin assay were collected via indwelling jugular catheters every 30 or 60 min from 12:00 to 22:00 h. In Expt 2B, 27 gilts were fed 1 mg of melatonin at 15:00 h each day from 129 days of age until slaughter at 221 days, while 25 gilts acted as controls. In both experiments, the presence of morphologically normal corpora lutea at slaughter was the criterion for puberty. In Expt 1, constant-release melatonin implants had no effect on the percentage of gilts which reached puberty. Among the 24 control gilts, two (8.3%) reached puberty compared with one of the 24 (4.2%) gilts with implants. In all the samples from control gilts, and in the samples taken from treated gilts prior to implantation at 126 days of age, mean plasma melatonin concentration was below the sensitivity of the assay (3.6 pg/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

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“…Further support for this hypothesis comes from experiments where hinds have been treated with melatonin for over a year, commencing in late winter before they had entered anoestrus. Prolactin concentrations remained suppressed and hinds continued to show repeated oestrous cycles throughout the entire treatment period (Adam et al 1989). In addition to the effects on prolactin, treatment with either drug is likely to have direct effects on the secretion of other pituitary hormones.…”

Section: Role Of Prolactin In Species With Photoperiodic Inhibition Omentioning

confidence: 99%

Seasonal prolactin secretion and its role in seasonal reproduction: a review

Jd¹

1992

Reprod. Fertil. Dev.

130

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The majority of seasonally breeding mammals show a seasonal pattern of prolactin secretion with peak concentrations in spring or summer and a nadir in autumn or winter. Photoperiod influences prolactin secretion via its effects on the secretion of the pineal hormone melatonin. Preliminary evidence suggests that the effects of melatonin on both prolactin and gonadotrophin secretion are via a common target area, possibly within the anterior hypothalamus, and that differences in response to photoperiod may be due to differences in the processing and/or interpretation of the melatonin signal. In contrast to seasonal gonadotrophin secretion, the seasonal changes in prolactin are not due to changes in the sensitivity of a feedback loop and so must be due to direct effects on the hypothalamic pathways that control prolactin secretion. Little else can be said with confidence about the neuroendocrine mechanisms that lead to the seasonal changes in prolactin secretion. Dopamine and noradrenaline turnover in the arcuate nucleus and median eminence decrease under short daylength. If catecholamine turnover in these structures is positively correlated with catecholamine concentrations in the long or short hypophysial portal vessels, it is unlikely that the decrease in prolactin concentration in winter is due to the effects of increased concentrations of dopamine or noradrenaline in the portal vessels. There is, however, evidence for increased pituitary sensitivity to dopamine under short daylength, so increased dopamine concentrations may not be required for suppression of prolactin secretion at this time. In addition to the diminished secretion of prolactin under short daylength, rate of prolactin synthesis and pituitary content of prolactin also decline although the mechanisms that regulate these changes are poorly understood.Although all seasonal breeders show a seasonal change in prolactin secretion, there are continuously breeding species in which prolactin secretion is also under photoperiodic control. It is likely therefore that a seasonal pattern of prolactin secretion is only evidence of neuroendocrine sensitivity to changing photoperiod. Depending upon the species, this sensitivity to the seasonal changes in daylength may or may not be accompanied by seasonal changes in a biological endpoint such as seasonal reproduction or indeed other adaptations. Whether the seasonal change in prolactin secretion is an endocrine mediator of such adaptations remains in contention. Certainly in some species this signal does have a role in reproduction. For example, in species with an obligate seasonal embryonic diapause, the seasonal increase in prolactin can act as a luteotrophin (mink and western spotted skunk) or luteostatin (Bennett's and tammar wallabies). In species where seasonal anoestrus or oligo-or azoospermia are due to a direct effect of photoperiod on gonadotrophin secretion, the seasonal changes in prolactin levels may also have been used by some species to influence seasonal reproduction. For example, the increase in ...

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Melatonin can induce year-round ovarian cyclicity in red deer (Cervus elaphus)

Cited by 15 publications

References 16 publications

Reproductive seasonality in domestic sows kept outdoors without boars

Reproductive seasonality in domestic sows kept outdoors without boars

Seasonal inhibition of puberty in domestic gilts is overcome by melatonin administered orally, but not by implant

Seasonal prolactin secretion and its role in seasonal reproduction: a review

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