Effect of Melatonin Feeding on Serum Prolactin and Gonadotropin Levels and the Onset of Seasonal Estrous Cyclicity in Sheep*

Kennaway, David J.; Gilmore, T. A.; Seamark, R.F.

doi:10.1210/endo-110-5-1766

Cited by 205 publications

(114 citation statements)

References 16 publications

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“…This is the first demonstration that the daily administration of melatonin in the afternoon to rams housed under long days induces reactivation of the reproductive axis as predicted from studies in the ewe (Kennaway et al, 1982 of FSH which was evident within 3 weeks and full testicular activity occurred after 10-14 weeks.…”

Section: Discussionmentioning

confidence: 52%

“…A switch from long days to short days leads to an increase in the duration of melatonin secretion and this results in a resurgence of reproductive activity and the onset of the new breeding season. The administration of exogenous melatonin in the afternoon to sheep exposed to long days, which extends the exposure to melatonin, causes early onset of ovarian activity in ewes similar to that produced by transfer to short days (Kennaway et al, 1982;English et al, 1986;Wigzell et al, 1988). The protocol of administering melatonin in the afternoon to photo-inhibited rams was used in the current study to test the effectiveness of ML23 as a melatonin antagonist.…”

Section: Introductionmentioning

confidence: 99%

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Test of ML23 as an antagonist to the effects of melatonin in the ram

Lincoln¹,

Kelly²

1989

Reproduction

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Summary. In Exp. 1, four groups of 8 yearling Soay rams were housed under long days (16L:8D) to induce reproductive quiescence and were treated daily for 12 weeks with: (I) vehicle (2 or 4 ml 50% ethanol/water), (II) ML23 (2 mg), (III) melatonin (2 mg) and (IV) melatonin and ML23 (2 mg of each). All treatments were given orally in the mid-light phase. In the rams receiving melatonin (Group III) there was an earlier increase in the plasma concentrations of FSH and testosterone and regrowth of the testes compared to the controls (time to maximum testicular diameter: 10\m=.\0 \ m=+-\ 0\m=.\5and 15\m=.\3\m=+-\1\m=.\2 weeks). These differences were reversed after the end of the 12-week treatments when rapid testicular regression occurred in melatonin-treated rams but not in the controls. In the group receiving ML23 and melatonin (Group IV), there was early reactivation and regression of the reproductive axis as in the melatonin group (testis max. 9\m=.\9\ m=+-\ 0\ m=. \ 7 and 10\m=.\0\ m=+-\ 0\ m=. \ 5weeks) while in the group receiving ML23 alone (Group II) there was a slower redevelopment and regression as in the controls (testis max. 15\m=.\7\m=+-\1\m=.\1and 15\m=.\3\m=+-\1\m=.\2 weeks). The comparison between the 4 groups in the changes in the blood concentrations of prolactin, voluntary food intake and total body weight also indicated that the treatment with ML23 failed to modify the effect of melatonin (combined treatment vs melatonin) or the effect of the long day photoperiod (ML23 vs vehicle).In Exp. 2, a more soluble derivative of ML23 (called ML23-lysine) was tested in two groups of 4 adult Soay rams which were housed under long days (16L:8D) and treated daily for 12 weeks, as above with: (I) melatonin (2 mg) and (II) melatonin (2 mg) and ML23-lysine (4 mg). In both groups there was a similar reactivation and regression of the testes with no significant differences between the two treatments.The overall results illustrate that the treatments with melatonin in this protocol were effective at influencing a wide range of reproductive and non-reproductive measures in the ram, but that ML23 was unable to antagonize these biological effects of melatonin.

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Section: Discussionmentioning

confidence: 52%

Section: Introductionmentioning

confidence: 99%

Test of ML23 as an antagonist to the effects of melatonin in the ram

Lincoln¹,

Kelly²

1989

Reproduction

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“…Confirmation of a gonadal response to melatonin treatment was provided in 1982 when it was shown that daily melatonin (8 h before darkness) feeding advanced the onset of ovarian cyclicity in ewes (Kennaway, Gilmore and Seamark, 1982a). Independent confirmation of the ability of melatonin treatments to advance the breeding season and decrease prolactin followed (Nett and Niswender, 1982 ;Arendt et al, 1983 ; Symons, Arendt and Laud, 1983 (Kennaway and Gilmore, 1984 ;Kennaway et al, 1986).…”

Section: Introductionmentioning

confidence: 97%

Short- and long-term effects of manipulation of the pineal/melatonin axis in ewes

Kennaway

1988

Reprod. Nutr. Dévelop.

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“…However, as the transition to fall began concentrations of prolactin fell significantly earlier in Group H females. Although melatonin treatment to ewes results in a fall in serum prolactin concentrations within 3 weeks (Kennaway et al, 1982), treatment of ram (Kennaway & Gilmore, 1985) and ewe (Kennaway et (Schultz & Terasawa, 1985). The question remains then whether initiation of short-day melatonin treatment 12 months earlier at 11 months of age might have reset the clock regulating the occurrence of first ovulation.…”

Section: Introductionmentioning

confidence: 99%