Regulation of the oestrous cycle in the ewe

Cumming, I. A.; Jm, Brown; Ma, Blockey; Goding,

doi:10.1530/jrf.0.0240148

Cited by 17 publications

(8 citation statements)

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“…The reasons for this are not clear. Cumming, Brown, Blockey & Goding (1971) have suggested that progesterone infusion into ewes may suppress the LH surge caused by oestradiol, and it is possible that, in the present study, the slightly elevated plasma progesterone levels at the time of oestrogen injection (Day 2) may have suppressed or reduced the response to oestradiol. It is also possible that the stimulus for a plasma gonadotrophin surge initiated by implant removal may have resulted in a block to oestradiol action.…”

Section: Discussionmentioning

confidence: 60%

The Effect of Progesterone Implants on Ovulation and Plasma Levels of Lh, FSH and Progesterone in Anoestrous Ewes

Saba¹,

Cunningham²,

Symons³

et al. 1975

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Section: Discussionmentioning

confidence: 60%

The Effect of Progesterone Implants on Ovulation and Plasma Levels of Lh, FSH and Progesterone in Anoestrous Ewes

Saba¹,

Cunningham²,

Symons³

et al. 1975

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“…While circulating progesterone can be associated with failure of oestrogen-positive feedback (Cumming et al 1971;Scaramuzzi et al 1971) the lack of detectable plasma progesterone suggests this was not the reason in these ewes. In ovine pregnancy pituitary LH content and the amount of LH released in response to exogenous LH-RH is markedly decreased (Charnley et a1.…”

Section: Discussionmentioning

confidence: 90%

Pituitary Responsiveness to LH-RH in Post-partum Ewes Treated With Oestradiol-17ß and Failing to Show a Plasma LH Surge

Wright¹,

Stelmasiak²,

Wa³

1980

Aust. Jnl. Of Bio. Sci.

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Oestradiol-17 p (40 fig intravenously) failed to elicit a surge in plasma LH levels by 13 h after administration in 64 % (16 out of 25) Merino ewes about 30 days post partum in the anoestrous season.LH-RH responsiveness and LH-RH priming effect were significantly greater in these ewes than in similar post-partum (n = 9) and non-parturient ewes (n = 3) not treated with oestradiol. This suggests that the failure of the oestrogen-positive feedback effect on LH release in post-partum ewes is not due to a failure of oestradiol action on the pituitary increasing pituitary responsiveness to LH-RH and LH-RH priming effect, but could be due to inadequate release of LH-RH from the hypothalamus.

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“…Pituitary responsiveness, however, is influenced by the levels of ovarian hormones. Treatment with oestradiol-17ß or LH-RH has a greater effect on LH release at the onset of behavioural oestrus than during the luteal phase (Bolt, Kelly & Hawk, 1971;Cumming, Brown, Blockey & Goding, 1971;Foster & Crighton, 1976). In the present study we have looked for possible changes in pituitary responsiveness to LH-RH during the reproductive cycle and investigated the relationship between responsiveness and the concentration of pituitary LH.…”

Section: Introductionmentioning

confidence: 99%

Pituitary responsiveness to synthetic LH-RH and pituitary LH content at various reproductive stages in the sheep

Jenkin¹,

Heap²,

Symons³

1977

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In sheep the basal concentration of LH in jugular vein plasma was significantly higher during the first 50 days of gestation in late pregnancy or at parturition. The pituitary response to a single i.v. injection of 200 microng synthetic LH-RH was determined at different stages of gestation and compared with that of anoestrous and cyclic sheep. Pituitary response to LH-RH decreased progressively with advancing gestation: by 56 days after mating the response had declined to 35% and by parturition to 14% of the value in anoestrous sheep. The pituitary response to LH-RH increased after parturition and the pattern of recovery differed in non-lactating and lactating sheep. By 63 days postpartum the response to LH-RH in non-lactating and lactating animals had returned to values similar to those in sheep during anoestrus and sheep during the luteal phase of the oestrous cycle. A decrease in pituitary responsiveness during pregnancy was associated with a decrease in pituitary content of LH. The quantity of LH released in response to a standard injection of LH-RH was linearly related to pituitary LH content.

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Regulation of the oestrous cycle in the ewe

Cited by 17 publications

References 0 publications

The Effect of Progesterone Implants on Ovulation and Plasma Levels of Lh, FSH and Progesterone in Anoestrous Ewes

The Effect of Progesterone Implants on Ovulation and Plasma Levels of Lh, FSH and Progesterone in Anoestrous Ewes

Pituitary Responsiveness to LH-RH in Post-partum Ewes Treated With Oestradiol-17ß and Failing to Show a Plasma LH Surge

Pituitary responsiveness to synthetic LH-RH and pituitary LH content at various reproductive stages in the sheep

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