FSH and LH Response to Gonadotropin-Releasing Hormone During the Ovine Estrous Cycle and Following Progesterone Administration<sup>1</sup><sup>2</sup>

Hooley, R. D.; Baxter, Robert W.; Chamley, W. A.; Cumming, I. A.; Jonas, Helen A.; Findlay, J. K.

doi:10.1210/endo-95-4-937

Cited by 40 publications

(18 citation statements)

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“…The plasma LH and FSH secretion (area units) for the 6-h period was estimated for each ewe as the area under the curve formed by joining the plasma concentration of the hormone (ng ml-I ) at each 15-min interval by a straight line (1 area unit = 1 ngml-I x 1 h) (Hooley et al 1974). The mean secretion of each group was compared to that of controls by Student's t-test.…”

Section: Analysis Of Resultsmentioning

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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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: Analysis Of Resultsmentioning

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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“…Mean LH response as calculated from the area under the response curve (Hooley et al 1974) was 153 ± 104 area units for clover-diseased ewes and 74 ± 58 area units for controls.…”

Section: Series Imentioning

confidence: 99%

Hypothalamic-Pituitary Function in Normal Ewes and Ewes which Grazed Oestrogenic Subterranean Clover for Several Years

Wa¹,

Adams²,

Rd³

et al. 1981

Aust. Jnl. Of Bio. Sci.

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Plasma luteinizing hormone (LH) concentrations were measured in normal Merino ewes and in Merino ewes with lowered fertility which had resulted from prolonged grazing of Trifolium subterraneum L. cv. Dinninup. During the anoestrous season, LH was measured at frequent intervals before and following administration of oestradiol-17 P or gonadotrophin releasing hormone (GnRH), and around the time of spontaneous oestrus.All ewes responded to GnRH treatment and there were no differences between the two groups in terms of the amount of LH released or the time to reach maximal plasma hormone concentration.Comparable proportions of ewes from both groups responded to oestradiol-17 p treatment with LH levels showing initially a negative feedback response (i.e. suppression to approximately 80 % of pretreatment levels) followed by positive feedback response. During the positive feedback phase, the quantity of LH which was released was comparable in both groups; however, the time interval over which this hormone was secreted was significantly shorter for clover-infertile ewes (P < O' 05).During the anoestrous season the mean LH level was lower in normal ewes than in clover-infertile ewes [0·45±0·41 (n = 31) versus 0·82±0·73 (n = 48) ng/ml, P < 0'01]. In the oestrous season the mean LH level for normal ewes rose to 1·23 ± O· 65 ng/ml (n = 76) but there was no change for the clover-infertile ewes (0·77 ± O· 59 ng/ml, n = 73). These experiments indicate that in the clover-infertile ewe LH concentration remains static throughout the breeding and non-breeding seasons but the results suggest that this altered endocrine status is not due to any differing level of sensitivity to negative feedback effects of oestradiol-17 p as compared with normal ewes.

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“…Estrogen (E) treatment of ovariectomised (OVX) ewes causes a delayed transient increase in the release of GnRH into the hypophysial portal circulation [3, 4]and enhances the sensitivity of gonadotropes to GnRH [5, 6, 7]and this combined action triggers a surge in the secretion of LH. A similar positive feedback action of E on the pituitary gland operates in the preovulatory period of ovary-intact animals and contributes to the LH surge that triggers ovulation [8, 9]. The mechanism by which E exerts its effects on the pituitary are not entirely understood.…”

Section: Introductionmentioning

confidence: 99%

Estrogen Transiently Increases Delayed Rectifier, Voltage-Dependent Potassium Currents in Ovine Gonadotropes

Cowley¹,

Chen²,

Clarke³

1999

Neuroendocrinology

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Treatment of gonadotropes with estrogen (E) changes the electrophysiological response to gonadotropin-releasing hormone (GnRH) such that the cells are hyperpolarised immediately after stimulation with GnRH and then generate action potentials more frequently than non-E-treated cells. We investigated the role of K⁺ current in this altered response to GnRH using cultures of ewe pituitary cells enriched for gonadotropes. K⁺ current density was measured using nystatin-perforated whole-cell recordings in the voltage clamp mode. Treatment of cells with E for 16–20 h significantly (p < 0.01) increased the unit K⁺ current to 180% of that in vehicle-treated cells. Outward current in these cells flows predominantly through voltage-dependent, delayed rectifier K⁺ channels (I_K), and E alters the magnitude of this current. The effect of E to increase the K⁺ current was dose- and time-dependent and was maximal after 16–20 h. The unit K⁺ current values returned to pre-treatment levels after 36 h of E treatment. Several cells were studied both before and after E treatment and the average effect of E on these cells was to increase the unit K⁺ current by 90%. The time-course of the effect of E on K⁺ current density is the same as the effect of E to increase LH release in vitro and in vivo. We conclude that the increase in K⁺ current may be an important part of the mechanism whereby E acts on gonadotropes to facilitate the LH surge which triggers ovulation.

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FSH and LH Response to Gonadotropin-Releasing Hormone During the Ovine Estrous Cycle and Following Progesterone Administration¹²

Cited by 40 publications

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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

Hypothalamic-Pituitary Function in Normal Ewes and Ewes which Grazed Oestrogenic Subterranean Clover for Several Years

Estrogen Transiently Increases Delayed Rectifier, Voltage-Dependent Potassium Currents in Ovine Gonadotropes

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FSH and LH Response to Gonadotropin-Releasing Hormone During the Ovine Estrous Cycle and Following Progesterone Administration12

Cited by 40 publications

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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

Hypothalamic-Pituitary Function in Normal Ewes and Ewes which Grazed Oestrogenic Subterranean Clover for Several Years

Estrogen Transiently Increases Delayed Rectifier, Voltage-Dependent Potassium Currents in Ovine Gonadotropes

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FSH and LH Response to Gonadotropin-Releasing Hormone During the Ovine Estrous Cycle and Following Progesterone Administration¹²