Plasma Prolactin in the Oestrous Cycle of the Ewe: Effect of Pituitary Stalk Section

Bryant, Gillian D.; Greenwood, F. C.; Kann, G.; Martinet, J.; Denamur, R

doi:10.1677/joe.0.0510405

Cited by 21 publications

(16 citation statements)

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“…In male lambs, castration or immunoneutralization of oestradiol are able to induce a modification of both LH secretion and DA content in the SME without altering PRL secretion (11). In adult ewes, stalk section only induced a transient increase in PRL release (19,20) and D A was absent from the capillaries of long portal vessels (21). In sheep, this amine could reach the pituitary through a more dorsal or posterior route as suggested by the increase in PRL secretion after premammillary deafferentations (6) or lesion of the hypothalamo-hypophysial tract posterior to the SME (22) in this species.…”

Section: Discussionmentioning

confidence: 98%

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: 98%

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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“…4). Since the prolactin release triggered by TRH was inhibited by the compound 2-Br-a-ergocryptinemethansulphonate (Schams, 1972b;Schams, Reinhardt & Karg, 1973) (2) A treatment using the same dose around the time of onset of lactation in cows (8 days ante partum up to 8 days post partum) resulted in a 10 to 30% increase of the first 20 days milk yield compared with the performance 1 year before (Schams, 1973;Schams et al, 1973 (Kuhn, 1970 (Reeves, Arimura & Schally, 1970;Bryant, Greenwood, Kann, Martinet & Denamur, 1971). The results in the cow are contradictory.…”

Section: Specific Inhibition Of Prolactin Releasementioning

confidence: 99%

Prolactin Release in Cattle

Karg¹,

Schams²

1974

Reproduction

121

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“…In intact ewes, pituitary stalk section is followed by a continuous, low-level, prolactin secretion (Bryant et al, 1971). This damping of the secretion was attributed both to partial necrosis of the gland and to elimination of a possible prolactin releasing factor (PRF), while continuity of the secretion was ascribed to elimination of a prolactin inhibiting factor (PIF) (Kann and Denamur, 1973).…”

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confidence: 99%

“…FSH, LH and prolactin were measured by specific radioimmunoassay (RIA) according to Blanc and Poirier (1979), Pelletier et al (1968) and Kann (1971) (fig. 4).…”

mentioning

confidence: 99%

“…The small amplitude of the 15 to 18 hr FSH release, as compared with the initial level in spayed females, may be surprising at first sight. In cycling ewes, plasma FSH decreased 3 days before oestrus (Pant et al,1977 ;Cahill,1979) (Kann, 1971), with a spiking pattern of secretion appearing just before LH surge or simultaneously with it ; thus, these changes can be considered as OB-induced responses. Large individual variations exist, which have also been reported in pregnant females (Kann and Denamur, 1974) and in spayed ewes (Malven, 1975).…”

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confidence: 99%

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Effects of anterior and posterior hypothalamic deafferentation on gonadotrophin and prolactin secretion in ovariectomized ewes under hormonally induced oestrous cycles

Thiéry¹,

Blanc²,

Ravault³

et al. 1979

Ann. Biol. anim. Bioch. Biophys.

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Plasma Prolactin in the Oestrous Cycle of the Ewe: Effect of Pituitary Stalk Section

Cited by 21 publications

References 0 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

Prolactin Release in Cattle

Effects of anterior and posterior hypothalamic deafferentation on gonadotrophin and prolactin secretion in ovariectomized ewes under hormonally induced oestrous cycles

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