Factors Affecting the Secretion of Luteinizing Hormone in the Ewe

Martin, Graeme

doi:10.1111/j.1469-185x.1984.tb00401.x

Cited by 171 publications

(87 citation statements)

References 519 publications

(266 reference statements)

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“…Furthermore, the data collected in our experiment improve our knowledge of the involvement of these molecules in other hypothalamic structures which are known to play a role in the regulation of reproduction in the ewe (16). Hormonal secretions were in keeping with the expected effect of the photoperiod and steroid treatment (1)(2)(3)(4)(5) i.e. the frequency of LH pulses was lower during long days in ewes bearing oestradiol implants.…”

Section: Discussionmentioning

confidence: 76%

Monoamine Content of the Stalk‐Median Eminence and Hypothalamus in Adult Female Sheep as Affected by Daylength

Thiéry

1991

J Neuroendocrinology

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In the ewe, plasma luteinizing hormone and prolactin concentrations exhibit seasonal variations. During long days, inhibition of pulsatile luteinizing hormone secretion is mediated by monoamines. In a model of ovariectomized ewes bearing a subcutaneous oestradiol implant, we previously showed that the steroid-dependent inhibition of luteinizing hormone involves the A15 dopaminergic nucleus of the retrochiasmatic area. In the present work, we compared the aminergic activities of tele-diencephalic structures in groups of ovariectomized ewes under artificial illumination for short versus long days (8 versus 16 h/day of light, respectively). Half the animals in each group were bearing a subcutaneous oestradiol implant. Using high-performance liquid chromatography and electrochemical detection, we measured the levels of amines and amine metabolites in 'punches' of tissues from regions containing luteinizing hormone-releasing hormone axon terminals or cell bodies and catecholaminergic structures. Concurrently, we checked the pulsatile luteinizing hormone release and plasma prolactin concentration to assess the ability of our model to mimic seasonal changes in the hormonal status.As expected, ovariectomized ewes with a subcutaneous oestradiol implant showed an inhibition of the pulsatile luteinizing hormone release under long days. A higher concentration of plasma prolactin was also observed under long days, without any effect of the steroid treatment. Under this light regimen, statistically significant higher contents of dopamine than under short days were found in the stalk-median eminence. Larger contents of homovanillic acid, a dopamine metabolite, and 4-hydroxy-3-methoxyphenylethyleneglycol (MHPG), a noradrenaline metabolite were observed in the infundibular nucleus, while the catecholamines themselves remained unchanged. Furthermore, oestradiol also significantly increased the content of MHPG in the latter structure. During long days, animals without oestradiol treatment exhibited a significant lower content of noradrenaline in the A15 nucleus, without any alteration of the dopamine content. Daylength or oestradiol treatment had no significant effects on the levels of amines or amine metabolites in the preoptic or septa1 areas. Thus, our results in the ewe underline the role played by the medial basal hypothalamus in the catecholaminergic regulation of seasonal changes in hormone release and suggest modifications in the turnover of the neurotransmitters in some structures.In the ewe, which is a short day breeder, annual variations in the secretion of luteinizing hormone (LH) and prolactin (PRL) accompany seasonal changes in reproductive activity (1 -3). The seasonal effect on LH (4, 5 ) and PRL secretion (6) has also been demonstrated in the ovariectomized ewe. During the period corresponding to anoestrus in the intact animals, the frequency of LH pulses in the ovariectomized females was slightly lower than during the breeding season, (steroid-independent inhibition), but the effect was fully expressed wh...

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Section: Discussionmentioning

confidence: 76%

Monoamine Content of the Stalk‐Median Eminence and Hypothalamus in Adult Female Sheep as Affected by Daylength

Thiéry

1991

J Neuroendocrinology

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“…The GnRH neuroendocrine system -the fundamental controller of reproduction: the secretion of GnRH by the hypothalamus, and consequently luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland, are central to the reproductive process (review: Martin, 1984). There is a threshold frequency of GnRH pulses above which males will produce sperm and females will ovulate so, effectively, the 'decision' of an animal to reproduce or not is implemented through pathways, as yet not described, that control the production of GnRH.…”

Section: Dimension 3 -The Communication Dimensionmentioning

confidence: 99%

Interactions between nutrition and reproduction in the management of the mature male ruminant

Martin¹,

Blache²,

Miller³

et al. 2010

Animal

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In mature male sheep and goats, changes in feed intake seem to have little effect on gonadal endocrine function but induce profound changes on sperm production. These outcomes are due to changes in size of the seminiferous tubules and in spermatogenic efficiency. Except with severe underfeeding, there are only minor changes in the endocrine function of the testis (testosterone production) unless season-long treatments are imposed. For cattle, nutrition clearly affects testicular development and the production of spermatozoa in young bulls, as it does in other species but, after the period of rapid growth has ended, there appears to be little or no response to nutrition. We are developing a clear picture of the metabolic signals, neuroendocrine processes and hormonal control systems that are involved, particularly for the mature male sheep. The energetic components of the diet, rather than protein, seem to be responsible, so we have envisaged a model of the relationship between energy balance and reproduction that has 4 'dimensions': genotype, structure (organs), communication (chemical and neural signals, nutrient sensing) and time (dynamics, metabolic memory, programming). We have linked these perspectives to 'resource allocation theory' and incorporated them into strategies for 'clean, green and ethical animal production'. In contrast to the clear outcomes with respect to spermatogenesis, the effects of nutrition on sexual behaviour are more difficult to define, perhaps because the behaviour is affected by a complex mix of physiological factors and because of flawed methods for quantifying male behaviour. For example, sexual behaviour is compromised by severe feed restriction, but male sexual behaviour requires intensive motor activity so a decline in libido could be caused by general weakness rather than specific nutritional limitations. The interaction between sexual activity and feeding behaviour also complicates the issue under field conditions. At the other end of the scale, overweight males can show reduced sexual success because they have difficulty courting and mounting. For this reason, exercise can enhance the fertilising capacity of rams. This will be important in extensive mating systems where males need to assemble and guard a harem and then mate many times for several weeks. For artificial insemination centres, there seems to be very few data on the nutritional management of males, but problems with overfed animals appear to be a risk. Future research should concentrate on the intra-testicular systems mediating the effects of nutrition on the production of spermatozoa.

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“…However, there is little information about the effects of estradiol on follicular dynamics in ewes. Administration of estradiol-17β to anestrous ewes induces an LH surge (for a review see [20]) and causes regression of the dominant follicle and the emergence of a new follicular wave approximately 3 days later [21]. The aim of this work was to study the relationship between the growth status of the largest follicle present when rams are introduced and the pattern of ovarian response in non-treated ewes and in ewes treated with estradiol-17β before ram introduction.…”

Section: Introductionmentioning

confidence: 99%

Response of anestrous ewes to the ram effect after follicular wave synchronization with a single dose of estradiol-17?

Ungerfeld

Dago

Rubianes³

et al. 2004

Reprod. Nutr. Dev.

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-Anestrous ewes respond to the introduction of rams with either an ovulation within 2-3 days that may be followed by luteal phases of normal or short length, with delayed ovulations (5-6 days later), or with the luteinization of follicles. The aim of this work was to study the relationship between the growth status of the largest follicle present when rams are introduced and the type of ovarian response in non-treated ewes and in ewes treated with estradiol-17β before ram introduction. Thirteen anestrous Corriedale ewes were divided into 2 groups: E2 (n = 7) and C (n = 6). The E2 ewes received a single dose of 50 µg estradiol-17β 5 days before the introduction of the rams to synchronize the onset of their follicle waves, while C ewes remained untreated. When the rams were introduced, all E2 ewes had the largest follicle in a growing stage in contrast with the C ewes (3 out of 6; P < 0.05). Five C and 4 E2 ewes ovulated after the introduction of the rams (Day 3.4 ± 0.4 for C vs. 4.8 ± 0.3 for E2 ewes, respectively, P < 0.05). Only one ewe from each group developed a normal luteal phase; 4 C and 3 E2 ewes had short luteal phases. One C ewe and 2 E2 ewes had short luteal phases originating from follicles that did not ovulate. After the first luteal phase, all ewes returned to anestrus without a second ovulation or luteal phase. The remaining E2 ewe did not ovulate or show any changes in progesterone serum concentrations. We conclude that the growth status of the largest follicle alone does not determine the ovarian responding pattern of anestrous ewes to the ram effect. follicular dynamics / ultrasound / ram stimulus / ovulation / non-breeding season

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Factors Affecting the Secretion of Luteinizing Hormone in the Ewe

Cited by 171 publications

References 519 publications

Monoamine Content of the Stalk‐Median Eminence and Hypothalamus in Adult Female Sheep as Affected by Daylength

Monoamine Content of the Stalk‐Median Eminence and Hypothalamus in Adult Female Sheep as Affected by Daylength

Interactions between nutrition and reproduction in the management of the mature male ruminant

Response of anestrous ewes to the ram effect after follicular wave synchronization with a single dose of estradiol-17?

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