Induction of plasma LH surges and normal luteal function in acyclic post-partum ewes by the pulsatile administration of LH-RH

Wright, Patrick; Geytenbeek, PE; Clarke, I. J.; Findlay, J. K.

doi:10.1530/jrf.0.0710001

Cited by 21 publications

(4 citation statements)

References 7 publications

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“…The amount of LH needed to trigger a key reproductive event like ovulation also likely is excessive. Studies in the ewe have shown that pulsed infusion of either GnRH [16,27] or LH [28] can lead to ovulation with normal luteal function. Thus, despite the fact that preovulatory LH secretion normally takes the form of a surge, a prolonged period of high-frequency LH pulses might be entirely sufficient to trigger ovulation in a follicle that is highly responsive to LH, because it has been adequately primed with FSH and E [29].…”

Section: Discussionmentioning

confidence: 99%

Prenatal Programming of Reproductive Neuroendocrine Function: The Effect of Prenatal Androgens on the Development of Estrogen Positive Feedback and Ovarian Cycles in the Ewe1

Unsworth

Taylor

Robinson

2005

Biology of Reproduction

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Exposure of the female ovine fetus to male hormones during a sensitive window of in utero life causes disruption to reproductive function. In some animals, androgen exposure completely abolishes reproductive cycles, but in others, cycles are progressively lost with age. The present study tested two predictions: that noncycling, androgenized animals are unable to respond to estrogen with a preovulatory-like surge of LH (estrogen positive feedback), and that the androgenized animals that exhibit a progressive loss of cycles also show a progressive loss of estrogen positive feedback. Androgenized ewes were generated by injection of their mothers with testosterone propionate twice per week from Day 30 to Day 90 of pregnancy (term, 147 days). Control ewes received no injections. Whether ewes could exhibit estrogen positive feedback was tested on five occasions before puberty (30 wk) and once during the anestrous period. All control animals had repeated reproductive cycles in both the first and second breeding season, and all showed robust LH surges during test periods. Despite the fact that 64% of androgenized animals showed reproductive cycles, estrogen positive feedback could be demonstrated in only 6.1% of trials. Subsequent experiments revealed that the lack of response to estrogen in androgenized animals was not because of pituitary insensitivity to GnRH, a requirement for higher concentrations of estrogen, or a surge that was delayed relative to the time of estrogen administration. The mechanisms by which some androgenized ewes can produce normal reproductive cycles in the apparent absence of estrogen positive feedback are currently unknown.

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Section: Discussionmentioning

confidence: 99%

Prenatal Programming of Reproductive Neuroendocrine Function: The Effect of Prenatal Androgens on the Development of Estrogen Positive Feedback and Ovarian Cycles in the Ewe1

Unsworth

Taylor

Robinson

2005

Biology of Reproduction

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“…8-12 h: F. J. Karsch, personal communication) is less than that seen in Merino ewes (one per 4-5 h: Scaramuzzi & Baird, 1977). The frequency of pulses of LH control ovarian activity (McNeiUy et al, 1982;McLeod et al, 1982;Wright et al, 1984), and so differences between the breeds in the 'depth' of anoestrus are also related to the degree by which the hypothalamo-hypophysial axis is inhibited. Thus, in less seasonal breeds like the Merino the lower sensitivity of the hypothalamus to nega¬ tive feedback would ensure a higher level of gonadotrophic support for the ovaries throughout anoestrus, compared to the more highly seasonal breeds, such as the Suffolk.…”

Section: Discussionmentioning

confidence: 99%

Effects of breed, ovarian steroids and season on the pulsatile secretion of LH in ovariectomized ewes

Thomas

Pearce²,

Oldham³

et al. 1988

Reproduction

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The effects of season and of oestradiol and progesterone on the tonic secretion of LH were studied in ovariectomized Merino and Suffolk ewes, two breeds which differ markedly in the seasonal pattern of their reproductive activity. In the absence of exogenous steroids, the frequency of LH pulses was lower and the amplitude of the pulses was higher in anoestrus than in the breeding season for Merino and Suffolk ewes 30 days after ovariectomy. In long-term (190 days) ovariectomized ewes, this seasonal change in LH secretion was observed in Suffolk ewes only. During seasonal anoestrus, treatment of ewes with subcutaneous oestradiol-17 beta implants (3, 6 or 12 mm in length) decreased the frequency of LH pulses in a dose-dependent manner, with Suffolk ewes being far more sensitive to the inhibitory effects of oestradiol than Merino ewes. The lowest dose of oestradiol (3 mm) had no effect on the secretion of LH in Merino ewes, but reduced secretion in Suffolk ewes. Treatment of ewes with the highest dose of oestradiol (12 mm) completely abolished LH pulses in Suffolk ewes, whereas infrequent pulses remained evident in Merino ewes. During the breeding season, oestradiol alone had no effect on the pulsatile release of LH in either breed, but in combination with progesterone there was a significant reduction in LH pulse frequency. Progesterone effectively decreased LH secretion in both breeds in both seasons. It was concluded that differences between breeds in the 'depth' of anoestrus could be related to differences in the sensitivity of the hypothalamus to both negative feedback by oestradiol and the direct effects of photoperiod.

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“…Periods of reproductive quiescence induced by environmental variables commonly reflect variation in function at hypothalamic loci leading to reduced activity of the endogenous GnRH pulsegenerating mechanism (Karsch et al, 1984). Imposition of an exogenous GnRH pulse delivery system can therefore override seasonal (McLeod et al, 1982) and post-partum (Wright et al, 1984) anoestrus in sheep.…”

Section: Discussionmentioning

confidence: 99%

Induction of precocious puberty in ewe lambs by pulsatile administration of GnRH

Pirl

Adams²

1987

Reproduction

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Circhoral administration (250 ng/h, i.v.) of GnRH induced a preovulatory-like surge of LH and subsequent luteal function in 4 of 4 ewe lambs 1 month before expected date of puberty. Within 12h of the start of pulsatile delivery of GnRH, mean concentrations of immunoactive and bioactive LH increased significantly (P less than 0.05) and the LH surge occurred by 1.8 +/- 0.6 days of treatment. Mean concentrations of serum progesterone were elevated significantly (P less than 0.001) 3 days after the surge. The biopotency of LH (bioactive LH/immunoactive LH) before the GnRH-induced surge of LH did not differ from LH biopotency in ewe lambs receiving circhoral delivery of saline (0.41 +/- 0.05 and 0.46 +/- 0.04, respectively). Biopotency of LH declined markedly at the GnRH-induced LH surge (0.25 +/- 0.04), but biopotency of serum LH was significantly augmented (P less than 0.05) during the period of luteal activity (0.70 +/- 0.07). Regular oestrous cycles were observed in 3 of 4 ewe lambs after the 10-day GnRH treatment period. These results indicate that pulsatile delivery of GnRH is effective in inducing precocious puberty in ewe lambs. Increase in LH biopotency does not appear to be required in the pubertal transition to reproductive cyclicity in this species. Augmented LH biopotency may be important in support of luteal function after first ovulation.

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Induction of plasma LH surges and normal luteal function in acyclic post-partum ewes by the pulsatile administration of LH-RH

Cited by 21 publications

References 7 publications

Prenatal Programming of Reproductive Neuroendocrine Function: The Effect of Prenatal Androgens on the Development of Estrogen Positive Feedback and Ovarian Cycles in the Ewe1

Prenatal Programming of Reproductive Neuroendocrine Function: The Effect of Prenatal Androgens on the Development of Estrogen Positive Feedback and Ovarian Cycles in the Ewe1

Effects of breed, ovarian steroids and season on the pulsatile secretion of LH in ovariectomized ewes

Induction of precocious puberty in ewe lambs by pulsatile administration of GnRH

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