The induction of ovulation and luteal function in seasonally anoestrous ewes treated with small-dose multiple injections of Gn-RH

McLeod, B. J.; Haresign, W.; Ge, Lan

doi:10.1530/jrf.0.0650215

Cited by 116 publications

(57 citation statements)

References 12 publications

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“…In anovular ewes, progesterone treatment prior to either the introduction of rams or treatment with GnRH, results in normal functioning of the corpora lutea that develop following the first ovulation (Hunter et al 1971;Oldham et al 1980;McLeod et at. 1982;Martin and Scaramuzzi 1983).…”

Section: Discussionmentioning

confidence: 99%

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Effects of Ovarian Hormones on Ovarian Capillary Blood Flow in Anoestrous Ewes

Brown¹,

Mattner²

1984

Aust. Jnl. Of Bio. Sci.

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The indicator fractionation technique with [86Rb ]rubidium chloride as the indicator was used to determine the relative blood flow (RBF) as a measure of capillary blood flow in the ovaries of conscious, hormonally treated, anoestrous ewes. Treatment of ewes with either progesterone only or oestradiol only had no effect on ovarian RBF, but treatment with oestradiol subsequent to progesterone caused a significant increase (P< 0.(01).Consequently, it appears that progesterone-induced sensitivity of the ovarian vasculature to the vasodilatory effects of oestradiol may be responsible for increased ovarian blood flow around oestrus in cyclic ewes.

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Section: Discussionmentioning

confidence: 99%

“…1982;Martin and Scaramuzzi 1983). It has been suggested that this effect may be due to progesterone delaying the onset of the induced LH surge, thereby allowing adequate follicular development to take place before the induction of ovulation (Hare sign and Lamming 1978;McLeod et at. 1982;Pearce et at.…”

Section: Discussionmentioning

confidence: 99%

Effects of Ovarian Hormones on Ovarian Capillary Blood Flow in Anoestrous Ewes

Brown¹,

Mattner²

1984

Aust. Jnl. Of Bio. Sci.

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“…The premature demise of the corpora lutea after exogenous gonadotropin stimulation is a poorly understood cause of embryo recovery failure that is reported following gonadotropin-releasing hormone (GnRH)-induced ovulation in anestrous ewes (McLeod et al, 1982), although progestagen priming before ovulation induction eliminates premature luteolysis in those females (McLeod et al, 1984;Southee et al, 1988). Inadequate luteal function has also been reported in superovulated ewes following oestrous synchronization using a dual prostaglandin injection treatment (Trounson et al, 1976;Schiewe et al, 1991).…”

Section: Luteal Activitymentioning

confidence: 99%

Effect of exogenous melatonin on the ovary, the embryo and the establishment of pregnancy in sheep

Abecia¹,

Forcada²,

Casao³

et al. 2008

Animal

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Administration of melatonin to advance the breeding season in sheep has been widely used, since this hormone conveys the photoperiodic signal to the reproductive neuroendocrine axis. An increased lambing percentage has been reported following such treatment during anoestrus, which could be mediated through a higher rate of embryonic survival, either by an improvement in luteal function or by a reduction in the antiluteolytic mechanisms. The aim of this article is to review the body of knowledge on the effect of melatonin on the ovine ovary, the embryo and the establishment of pregnancy. Some studies using synchronized ewes have found that melatonin treatments during anoestrus do not improve ovulation rate by modifying the timing of follicle emergence, but increasing the number of ovulatory follicles by decreasing the atresia of medium and large follicles. On the other hand, the addition of melatonin to the in vitro maturation medium does not improve oocyte maturation rate in oocytes from sheep ovaries recovered either in anoestrus or in the breeding season. However, a luteotrophic effect of melatonin at either short or medium term has been reported. We have recently observed that melatonin implants tend to improve the survival of embryos collected from ewes after superovulation in anoestrus. More specifically, melatonin induced a significant reduction of the number and rate of non-viable (degenerate and retarded) embryos. Preliminary data from our laboratory suggest that the uterine sensitivity to progesterone -in terms of progesterone receptor expression -of superovulated ewes could be reduced by melatonin treatment. It can be concluded that the success of exogenous melatonin as a means to improve lamb production of sheep is due, at least in part, to an improvement of luteal support and embryonic survival.

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“…The CL formed tend to be smaller and secrete less progesterone in vivo and in vitro than CL of the breeding season (McNeilly & Land 1979. Increasing the frequency of LH (McNeilly et al 1982) or GnRH pulses (Crighton et al 1975, McLeod et al 1982a, 1982b, Southee et al 1988a, 1988b to mimic the final stages of follicular maturation during the breeding season increased ovulation rate during seasonal anoestrus but still gave rise frequently to abnormal CL. However, the incidence of adequate luteal phases during anoestrus was increased significantly by progesterone pretreatment prior to induction of ovulation with GnRH (McLeod et al 1982b, Legan et al 1985.…”

Section: Introductionmentioning

confidence: 99%

“…A number of different mechanisms have been suggested to be responsible for the formation of inadequate luteal phases in sheep, including defective maturation of the preovulatory follicle (Keisler & Keisler 1989, Hunter et al 1986, White et al 1987, Southee et al 1988a, Khalid et al 1997, Lund et al 1999, Bartlewski et al 2001, perhaps due to an inappropriate pattern of LH stimulation of the follicle prior to the LH surge (McLeod et al 1982a, Wright et al 1983, attenuation of the LH surge (Bartlewski et al 2004), inadequate luteinization (Atkinson 1988, Hunter et al 1988, inappropriate luteal support of the new CL (Hunter et al 1988) and/or increased susceptibility to luteolytic stimuli (Hunter et al 1989, Beard & Hunter 1996 arising from the uterus (Southee et al 1988b, Hu et al 1991, though see Rahmanian and Murdoch 1987).…”

Section: Introductionmentioning

confidence: 99%

Corpora lutea induced by gonadotrophin-releasing hormone treatment of anoestrous Welsh Mountain ewes: reduced sensitivity to luteinizing hormone in vivo and to chorionic gonadotrophin in vitro

Bramley

Stirling²,

Menzies³

et al. 2005

Reproduction

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Seasonally anoestrous Welsh Mountain ewes received 250 ng gonadotrophin-releasing hormone (GnRH) every 2 h, with (Group 1;n= 13) or without (Group 2;n= 14) progesterone priming for 48 h. Fourteen control ewes (Group 3) were studied during the luteal phase in the breeding season. Animals in Group 4 (n= 12) received progesterone priming followed by 250 ng GnRH at increasing frequency for 72 h, while ewes in Group 5 (n= 13) were given three bolus injections of 30 μg GnRH at 90-min intervals. All treatment regimens induced ovulation. However, only corpora lutea (CL) from ewes in Group 3 (breeding season) or Group 4 exhibited normal luteal function. Luteal luteinizing hormone (LH) receptor levels were significantly higher on day 12 than day 4, and CL from groups with adequate CL (3 and 4) had significantly higher125I-human chorionic gonadotrophin (hCG)-binding levels than the three groups with inadequate CL on day 12. LH-binding affinity was unchanged. Exogenous ovine LH (10 μg)in vivoon days 3 or 11 after ovulation induced a pulse of progesterone in ewes with adequate CL: however, ewes in Groups 1, 2 and 5 showed no significant response. Basal progesterone secretionin vitrowas significantly greater on day 4 than on day 12. Maximal steroidogenic responses of adequate and inadequate CL to hCG and to dibutyryl cyclic-3′,5′-AMP were similar at both stages of the luteal phase. However, the EC50for hCG on days 4 and 12 was 10-fold lower for groups with an adequate CL (0.1 IU hCG/ml) than for inadequate-CL groups (1 IU hCG/ml;P<0.05). Thus, in addition to the well-characterized premature sensitivity of GnRH-induced inadequate CL to endometrial luteolysin, we have shown (1) a marked decrease in total number of cells in the CL, a profound reduction in vascular surface area, and a decrease in mean large luteal cell volume (with no change in large luteal cell numbers), (2) decreased luteal LH receptor and progesterone content compared with adequate CL and (3) that CL that were becoming, or were destined to become, inadequate failed to respond to ovine LHin vivoand were 10-fold less sensitive to hCG in terms of luteal progesterone secretionin vitro.

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The induction of ovulation and luteal function in seasonally anoestrous ewes treated with small-dose multiple injections of Gn-RH

Cited by 116 publications

References 12 publications

Effects of Ovarian Hormones on Ovarian Capillary Blood Flow in Anoestrous Ewes

Effects of Ovarian Hormones on Ovarian Capillary Blood Flow in Anoestrous Ewes

Effect of exogenous melatonin on the ovary, the embryo and the establishment of pregnancy in sheep

Corpora lutea induced by gonadotrophin-releasing hormone treatment of anoestrous Welsh Mountain ewes: reduced sensitivity to luteinizing hormone in vivo and to chorionic gonadotrophin in vitro

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