Plasma FSH, LH, the positive feedback of oestrogen, ovulation and luteal function in the ewe given bromocriptine to suppress prolactin during seasonal anoestrus

Land, R. B.; Carr, William; McNeilly, A. S.; Preece, R. D.

doi:10.1530/jrf.0.0590073

Cited by 33 publications

(21 citation statements)

References 11 publications

(12 reference statements)

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“…In group 2 the number of LH and T peaks was not affected by CB 154 during the treatment period, agreeing with the results of Land et al (1980). However, after treatment had finished, the number of peaks rose significantly.…”

supporting

confidence: 87%

Influence of 2 Br-α-ergocryptine (CB 154) on the secretion of prolactin, LH, FSH and testosterone and on testicular growth in rams subjected to different photoperiods

Ravault¹,

Barenton²,

Blanc³

et al. 1982

Reprod. Nutr. Dévelop.

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Summary. The influence of 2-Br-a-ergocryptine (CB 154) on the secretion of gonadotrophins and on testicular function has been studied in rams subjected to either a normal photoperiod or an abnormal photoperiod causing hyperprolactinaemia. The CB 154 treatment significantly lowered the mean frequency of LH and testosterone pulses in hyperprolactinaemic animals as compared to solvent-treated ones. Also, only those groups subjected to an abnormal photoperiod (groups 2 and 3) exhibited a significant rise in the frequency of LH and testosterone peaks after CB 154 was withdrawn. During treatment, plasma FSH concentrations increased significantly only in group 1 which was subjected to normal photoperiodic variations. Testicular growth was delayed in CB 154-treated rams compared to solvent-treated ones only in group 3 (hyperprolactinaemic).Introduction.

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supporting

confidence: 87%

Influence of 2 Br-α-ergocryptine (CB 154) on the secretion of prolactin, LH, FSH and testosterone and on testicular growth in rams subjected to different photoperiods

Ravault¹,

Barenton²,

Blanc³

et al. 1982

Reprod. Nutr. Dévelop.

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“…Whether prolactin is related to cyclic activity has been quite controversial, and although most investigations have not found a clear relationship [43,46], the timing of prolactin secretion manipulation may be crucial for an effect on reproductive activity. Indeed, when prolactin was suppressed towards the end of the estrous season, the season was found to be extended [6], whereas suppression of prolactin during the anestrous period did not affect the timing of onset of cyclic activity [19,33].…”

Section: Discussionmentioning

confidence: 97%

Seasonal changes in ovulatory activity, plasma prolactin, and melatonin concentrations, in Mouflon (Ovis gmelini musimon) and Manchega (Ovis aries) ewes

Santiago-Moreno¹,

López-Sebastián²,

González-Bulnes³

et al. 2000

Reprod. Nutr. Dev.

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-Seasonal changes in ovulatory activity, plasma prolactin and melatonin concentrations were monitored in a wild (Mouflon) and a domesticated (Manchega) breed of sheep, both originating and living under similar latitudes (40°N). Mouflons express ovarian cycles significantly later than Manchega ewes (October vs. July, P < 0.001); however, they ended cycling one month later than Manchegas (April vs. March, P < 0.05). While prolactin concentrations were high when Manchega ewes started to cycle, they were at their lowest concentrations when Mouflons started cycling. Overall, mean prolactin concentrations were higher (P < 0.001) in Mouflons than Manchegas throughout most of the year. Within the limits of sampling frequency, the duration of melatonin secretion was similar in both groups during the solstice and equinox periods; however, the amplitude was lower (P < 0.01) in Mouflons than Manchegas during the solstice periods. The significant breed differences in the seasonal hormonal changes may be attributed to a genetic influence in the endocrine responses to the same photoperiodic cues. Mouflon / sheep / breeding season / melatonin / prolactinRésumé -Variations saisonnières de l'activité ovulatoire, de la prolactine et de la mélatonine plasmatiques chez la femelle Mouflon (Ovis gmelini musimon) et la brebis Manchega (Ovis aries). Les variations saisonnières de l'activité ovulatoire et des concentrations plasmatiques de prolactine et de mélatonine ont été suivies dans une race ovine sauvage (Mouflon) et une race ovine domestique Reprod. Nutr. Dev. 40 (2000) [421][422][423][424][425][426][427][428][429][430] 421

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“…A common approach to this question has been to use pharmacological sup pression of plasma PRL by treatment with the dopamine ago nist bromocriptine. In several such studies there has been no effect of treatment on pulsatile LH secretion [28,29] or oestrous cyclicity [7,30]. However, as well as inhibiting PRL secretion, dopamine D?…”

Section: Discussionmentioning

confidence: 99%

Prolactin Short-Loop Feedback and Prolactin Inhibition of Luteinizing Hormone Secretion during the Breeding Season and Seasonal Anoestrus in the Ewe

Curlewis

McNeilly²

1991

Neuroendocrinology

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In seasonally breeding mammals, plasma prolactin (PRL) concentrations vary on an annual basis with levels high in summer and low in winter. In this study of the ewe, we determined, first, whether PRL secretion is regulated by short-loop feedback and, second, whether the high summer levels of PRL are due to a change in sensitivity or loss of this feedback loop. Because the high summer levels of PRL coincide with the period of seasonal anoestrus in the ewe and could therefore be involved in the seasonal suppression of gonadotrophins, the effects of intracerebroventricular PRL on pulsatile LH secretion were also determined. Ovary intact ewes received intracerebroventricular injections of ovine PRL (oPRL; 50 µg) or anti-PRL serum. From 3 to 13 h after central administration of oPRL, plasma PRL concentrations were significantly reduced compared with the vehicle-treated controls. In contrast, following injection of anti-PRL serum, plasma PRL levels increased significantly. To determine whether there was a seasonal change in sensitivity to PRL feedback, a series of experiments were conducted in July and November when PRL concentrations are high and low, respectively. At each time of year, ovariectomized oestradiol-implanted ewes were injected intra-cerebroventricularly with 10 and 50 µg oPRL with control animals receiving the vehicle. At both times of year there was clear evidence of PRL short-loop feedback with no indication that sensitivity was reduced in the July trial. Luteinizing hormone (LH) pulse frequency, pulse amplitude and mean LH were not affected by intracerebroventricular oPRL at either time of year. These results indicate that the high PRL concentrations of summer are not due to the absence of PRL short-loop feedback and that suppression of pulsatile LH secretion during seasonal anoestrus is unlikely to be due to inhibition by PRL.

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Plasma FSH, LH, the positive feedback of oestrogen, ovulation and luteal function in the ewe given bromocriptine to suppress prolactin during seasonal anoestrus

Abstract: Summary. The It is concluded that treatment with bromocriptine alone is unlikely to restore oestrous cycles to ewes in seasonal anoestrus.

Cited by 33 publications

References 11 publications

Influence of 2 Br-α-ergocryptine (CB 154) on the secretion of prolactin, LH, FSH and testosterone and on testicular growth in rams subjected to different photoperiods

Influence of 2 Br-α-ergocryptine (CB 154) on the secretion of prolactin, LH, FSH and testosterone and on testicular growth in rams subjected to different photoperiods

Seasonal changes in ovulatory activity, plasma prolactin, and melatonin concentrations, in Mouflon (Ovis gmelini musimon) and Manchega (Ovis aries) ewes

Prolactin Short-Loop Feedback and Prolactin Inhibition of Luteinizing Hormone Secretion during the Breeding Season and Seasonal Anoestrus in the Ewe

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