The release of luteinizing hormone by oestradiol-17  and a synthetic gonadotrophin-releasing factor in ewes affected with clover disease

Findlay, J. K.; Cumming, I. A.; Wa, Chamley; Jm, Buckmaster; Goding,; Hearnshaw, H

doi:10.1530/jrf.0.0320341

Cited by 22 publications

(22 citation statements)

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“…These results disagree with those previously reported by Findlay et al (1973) who used ovariectomized ewes in which the LH secretion responses to oestrogen were different from those in entire ewes (Brown et al 1972;Karsch et al 1977). Furthermore, the present results were corroborated in a study by W. A. Charnley (personal communication) who also demonstrated that clover-infertile ewes were more sensitive to the positive feedback effects of E2 , releasing LH earlier than normal ewes after treatment in anoestrus.…”

Section: Discussioncontrasting

confidence: 99%

“…In addition, there may be an associated neuroendocrine lesion. For example, Findlay et al (1973) have reported that when infertile ewes which had previously grazed oestrogenic clover were ovariectomized, they were less likely to show elevated plasma LH levels, i.e. positive feedback (Goding et al 1969), in response to oestradiol-17f1 (E 2 ) treatment than were normal ovariectomized ewes.…”

Section: Introductionmentioning

confidence: 99%

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Plasma LH and FSH in Ewes That Were Either Fertile or Infertile After Long-Term Grazing of Oestrogenic Pasture

Rodgers

Clarke

Findlay

et al. 1980

Aust. Jnl. Of Bio. Sci.

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The levels of plasma LH and FSH were measured in serial blood samples taken at 15-min intervals for 6 h from ewes that had remained fertile after grazing oestrogenic pasture (clover-fertile ewes), from ewes that were permanently affected by clover disease (clover-infertile ewes) and from normal ewes. Two flocks of ewes from different locations were studied. In flock I, tonic LH secretion (total area under the curve of LH concentration versus time, 1 area unit = 1 ng ml-1 x 1 h) was significantly (P < 0'05) greater in clover-infertile ewes (10'4 area units) during anoestrus than in ewes that had remained fertile after prolonged grazing of oestrogenic clover (5·4 area units). Tonic LH and FSH secretions during the breeding season and FSH secretion during anoestrus were not significantly different. In flock 2, LH levels during the breeding season were significantly (P < 0'05) elevated in clover-infertile ewes (10' 9 area units) compared to normal ewes (5' 4 area units) that had never grazed oestrogenic clover. LH secretion in clover-infertile ewes (7. 8 area units) was intermediate to that found in infertile and control ewes. Concentrations of FSH, progesterone and ovarian vein oestradiol-17 P (Ez) during the breeding season were similar in the three groups.In another experiment, the positive feedback release of LH following administration of Ez (12'5,25 or 50 f.1g per ewe) was measured in anoestrous ewes of flock 2. Significantly (P < 0·01) more clover-infertile ewes demonstrated a positive feedback effect than control ewes when given 12· 5 f.1g Ez but not when given higher doses.The elevation of LH secretion in permanently affected clover-infertile ewes is consistent with the hypothesis that the hypothalamo-pituitary axis of these ewes is less responsive to the negative feedback effect of oestrogen. Furthermore, the patency of the positive feedback loop is consistent with the ability to ovulate.Other keywords: Clover disease. IntroductionLong-term grazing of oestrogenic clover pastures may cause permanent infertility in ewes (Bennetts et al. 1946;Barrett et al. 1965) although not all ewes grazing oestrogenic clover exhibit infertility. Infertile ewes have uterine endometrial hyperplasia and changes in cell type and function of the cervix (Adams 1976). In addition, there may be an associated neuroendocrine lesion. For example, Findlay et al. (1973) have reported that when infertile ewes which had previously grazed oestrogenic clover were ovariectomized, they were less likely to show elevated plasma LH levels, i.e. positive feedback (Goding et al. 1969), in response to oestradiol-17f1 (E 2 ) treatment than were normal ovariectomized ewes. This reduced responsiveness of the hypothalamo-pituitary axis to E2 could be related to changes in the number or affinity

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Section: Discussioncontrasting

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Plasma LH and FSH in Ewes That Were Either Fertile or Infertile After Long-Term Grazing of Oestrogenic Pasture

Rodgers

Clarke

Findlay

et al. 1980

Aust. Jnl. Of Bio. Sci.

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“…This confirms the findings of Findlay et al (1973), and suggests that Rodgers et al (1980) and Charnley et al (1981) did not find this effect because they used entire ewes. Basal levels of LH are higher in entire affected ewes than in controls during anoestrus (Rodgers et al 1980;Charnley et al 1981), but not in ovariectomized ewes.…”

Section: Discussionsupporting

confidence: 84%

“…The initial report by Findlay et al in 1973 suggested that affected ewes were less able to produce a surge of LH, but in subsequent studies (Rodgers et al 1980;Charnley et al 1981) this difference did not occur.…”

Section: Introductionmentioning

confidence: 98%

“…Findlay et al (1973) were unable to obtain control ewes as old as the affected ewes studied (9-10 years old), and so the failure may have been due to the ewes' old age. Secondly, they studied ovariectomized ewes, while the subsequent studies were carried out on intact ewes during seasonal anoestrus, when endogenous levels of oestradiol are low.…”

Section: Introductionmentioning

confidence: 98%

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Effects of Oestradiol on Plasma Concentrations of Luteinizing Hormone in Ovariectomized Ewes with Clover Disease

Adams¹,

Martin²

1983

Aust. Jnl. Of Bio. Sci.

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The effects of oestradiol on plasma luteinizing hormone (LH) concentrations were examined in 15 ovariectomized control ewes and 15 similar ewes with permanent infertility after prolonged grazing on oestrogenic clover pasture ('clover disease'). Before treatment, the plasma concentrations of LH were similar in the control and affected ewes. After intravenous injection with 40 pg oestradiol-I 7 p during the anoestrous season, the decline in LH concentration was greater in the clover-affected ewes and the subsequent elevation above original baseline levels was smaller. After intramuscular injection with 15 or 30 pg oestradiol benzoate during the normal breeding season, fewer clover-affected ewes showed a surge of LH, and the response was both reduced and retarded. This difference between the two groups has not been observed in studies on intact ewes, and it is suggested that in intact ewes the difference is masked by a greater tonic LH activity in affected ewes. The results of the present study are consistent with the hypothesis that prolonged exposure to oestrogenic pasture has a differentiating, or 'androgenizing' effect on the adult ewe.

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Red Clover Derived Isoflavones: Metabolism and Physiological Effects in Cattle and Sheep and their Concentration in Milk Produced for Human Consumption

Taponen

Mustonen

Kontio

et al. 2010

Recent Advances in Polyphenol Research

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The release of luteinizing hormone by oestradiol-17 and a synthetic gonadotrophin-releasing factor in ewes affected with clover disease

Cited by 22 publications

References 0 publications

Plasma LH and FSH in Ewes That Were Either Fertile or Infertile After Long-Term Grazing of Oestrogenic Pasture

Plasma LH and FSH in Ewes That Were Either Fertile or Infertile After Long-Term Grazing of Oestrogenic Pasture

Effects of Oestradiol on Plasma Concentrations of Luteinizing Hormone in Ovariectomized Ewes with Clover Disease

Red Clover Derived Isoflavones: Metabolism and Physiological Effects in Cattle and Sheep and their Concentration in Milk Produced for Human Consumption

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