Abrupt decrease in daylength and short-term changes in the plasma concentrations of FSH, LH and prolactin in anoestrous ewes

Walton, J.S.; Evins, Janet D.; Fitzgerald, B. P.; Cunningham, F. J.

doi:10.1530/jrf.0.0590163

Cited by 55 publications

(40 citation statements)

References 15 publications

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“…Twenty-two days after a four hour reduction in light the prolactin levels in both control and melatonin treated ewes decreased to 5 % of the initial levels. These results confirmed in goats that one of the earliest physiological responses to short daylength was a precipitous drop in plasma prolactin (Walton et al, 1980) and that showed that exogenous melatonin could replicate this response.…”

Section: Introductionsupporting

confidence: 77%

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

Kennaway

1988

Reprod. Nutr. Dévelop.

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Section: Introductionsupporting

confidence: 77%

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

Kennaway

1988

Reprod. Nutr. Dévelop.

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“…In sheep, the pattern of circadian prolactin secretion varies during the year. In spring, a biphasic rhythm of prolactin secretion is observed, with highest levels before noon and in the evening [10, 11, 12]. Lowest levels occur before night-time.…”

Section: Introductionmentioning

confidence: 99%

Melatonin Modulation of the Daily Prolactin Secretion in Intact and Ovariectomized Ewes

1999

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The aim of this study was to investigate whether melatonin might modulate the daily prolactin secretion in the ewe during a period of ovarian activity and, if so, whether this modulatory action of melatonin was related to the presence of estradiol in the organism. Ewes in the late follicular and luteal phase, as well as overiectomized ewes without (OVX) and after 7 days of estradiol injections (OVX+E₂) were examined. Melatonin was infused into the third brain ventricle (100 µg/100 µl/h) from 14.00 to 18.00 h. The concentration of prolactin increased significantly during the infusion of melatonin in late follicular-phase ewes, but not in luteal-phase ewes, as compared to the concentration before the infusion: range from 204.0 ± 31.7 to 272.2 ± 50.1 ng/ml vs. range from 68.2 ± 31.8 to 94.7 ± 33.1 ng/ml (mean ± SEM, n = 4, p < 0.01) and to the concentration noted during control infusions: range from 130.0 ± 58.0 to 179.3 ± 55.6 ng/ml (mean ± SEM, n = 4, p < 0.05). In ovariectomized ewes, the concentration of prolactin during infusion of melatonin increased significantly, unrelated to the presence of estradiol, as compared to the concentration before infusion: range from 136.7 ± 20.3 to 260.0 ± 11.6 ng/ml vs. range from 41.6 ± 2.6 to 152.3 ± 14.6 ng/ml in OVX ewes (mean ± SEM, n = 4, p < 0.01) and range from 161.5 ± 66.5 to 250.2 ± 24.3 ng/ml vs. range from 61.2 ± 1.7 to 159.2 ± 43.3 ng/ml in OVX+E₂ ewes (mean ± SEM, n = 4, p < 0.01). Concentrations during infusion of melatonin in OVX and OVX+E₂ ewes were also significantly higher than during the control infusions: range from 7.2 ± 1.7 to 22.2 ± 4.1 ng/ml (mean ± SEM, n = 4, p < 0.001). These results indicate that melatonin may affect the daily secretion of prolactin in ewes during the breeding season, and suggest that the variable response of prolactin to the melatonin signal in intact and ovariectomized ewes relates to the interaction between both ovarian steroids – estradiol and progesterone – and the prolactin-releasing factor.

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“…2 h before lights off). Several other studies in pregnant and non-pregnant sheep have reported a similar 'lights off' or 'dusk' peak in prolactin concentrations (Brown & Forbes, 1980;Brinklow & Forbes, 1984;McMillen et al 1987McMillen et al , 1991Poulton, English, Symon & Arendt, 1989;Walton, Evins, Fitzgerald & Cunningham, 1989). The diurnal prolactin rhythm in the ewe persists after pinealectomy or after sympathetic denervation of the pineal gland which suggests that the presence of the pineal gland is not required for the generation of this rhythm (Lincoln, 1979;Brown & Forbes, 1980;Brinklow & Forbes, 1984;Poulton et al 1989;Maxwell, Rintoul, Foldes, Downing, Scaramuzzi & Carter, 1989;McMillen et al 1991).…”

Section: Prolactinmentioning

confidence: 80%

Effects of different lighting regimes on daily hormonal and behavioural rhythms in the pregnant ewe and sheep fetus.

McMillen

Walker

1991

The Journal of Physiology

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1. We have studied the effect of altering the time of darkness during a 12 h photoperiod on the diurnal rhythms of maternal and fetal plasma melatonin and prolactin concentrations and fetal breathing movements (FBMs) in the late pregnant sheep. 2. Four ewes were exposed to a ‘normal’ 12 h light‐12 h dark regime with lights off at 19.00 h. Eight ewes were exposed to an ‘altered’ 12 h light‐12 h dark regime with lights off at 11.00 h. FBMs were recorded continuously and 2 hourly maternal and fetal blood samples taken during 24 h experiments between 120 and 138 days gestation. 3. Plasma melatonin concentrations were higher during the hours of darkness in the ewes and fetuses in both the normal and altered groups; i.e. altering the time of darkness was associated with a shift in the timing of the daily increase in melatonin concentrations in the mother and fetus. 4. In the fetuses, the mean 24 h plasma prolactin concentration was higher in the altered lighting group (28.8 +/‐ 6.1 micrograms/l) compared to the normal lighting group (13.0 +/‐ 3.9 micrograms/l). There was no difference, however, between groups in the daily variation of fetal plasma prolactin concentrations, which were higher at 17.00‐01.00 h than at 05.00‐19.00 h. Thus, altering the time of darkness did not change the timing of the daily plasma prolactin rhythm in the fetus. 5. Under the normal lighting regime maternal plasma prolactin concentrations were higher at 17.00‐19.00 h (i.e. from 2 h before lights off) than at 09.00‐11.00 h. In contrast, under altered lighting, plasma prolactin concentrations were higher at 01.00‐07.00 h (i.e. 2‐8 h after lights on) than at 09.00 h. 6. In the normal lighting group the incidence (min/h) of FBMs were highest at 16.00‐21.00 h and reached a minimum at 05.00‐06.00 h. In contrast, in the altered lighting group the incidence of FBMs was lowest at 19.00‐20.00 h and reached a maximum at 11.00‐12.00 h. 7. The results suggest that the light‐dark cycle influences the diurnal modulation of FBMs, but not the daily variation of fetal plasma prolactin concentrations. The role of plasma melatonin concentrations, and evidence for a photo‐inducible phase of increased prolactin secretion in the fetus, is discussed.

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Abrupt decrease in daylength and short-term changes in the plasma concentrations of FSH, LH and prolactin in anoestrous ewes

Abstract: Summary. The

Cited by 55 publications

References 15 publications

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

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

Melatonin Modulation of the Daily Prolactin Secretion in Intact and Ovariectomized Ewes

Effects of different lighting regimes on daily hormonal and behavioural rhythms in the pregnant ewe and sheep fetus.

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