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Pituitary responses of seasonally anoestrous ewes to long-term continuous infusion of low doses of GnRH

Published online by Cambridge University Press:  02 September 2010

M. Khalid ,
W. Haresign ,
M. G. Hunter  and
B. J. McLeod
M. Khalid
Affiliation:
AFRC Research Group on Hormones and Farm Animal Reproduction, University of Nottingham, School of Agriculture, Sutton Bonington, Loughborough LE12 5RD
W. Haresign
Affiliation:
AFRC Research Group on Hormones and Farm Animal Reproduction, University of Nottingham, School of Agriculture, Sutton Bonington, Loughborough LE12 5RD
M. G. Hunter
Affiliation:
AFRC Research Group on Hormones and Farm Animal Reproduction, University of Nottingham, School of Agriculture, Sutton Bonington, Loughborough LE12 5RD
B. J. McLeod
Affiliation:
AFRC Research Group on Hormones and Farm Animal Reproduction, University of Nottingham, School of Agriculture, Sutton Bonington, Loughborough LE12 5RD
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Abstract

The response to long-term continuous infusion of gonadotrophin releasing hormone(GnRH)was monitored in progesterone-treated seasonally anoestrous ewes. Using osmotic pumps, groups of five ewes eachreceived 0(controls),125, 250, 500 or 1000 ng GnRH per h subcutaneously for a period of 21 days. Bloodsamples were collecte dat 30-minintervals from 6 h before until 24 h after the start of treatment and then for 8-h periods on days 2, 8, 15 and 21. After 21 days of treatment all the ewes were slaughtered to determine pituitary GnRH receptor numbers. Continuous infusion of GnRH resulted in a short-lived (2day)increase in plasma LH and oestradiol concentrations after which they were not different from the pre-treatment values. Over the later period of treatment when the pituitary gland was not responding to the exogenous GnRH(days 8, 15 and 21), LH episodes(presumably due to endogenous GnRH secretion fromthe hypothalamus) were observed. Continuous infusion of GnRH was also associated with a suppression in plasma FSH concentrations, the duration of which was dose-dependent. Only at the highest GnRH dose level(1000 ng/h)was there a significant reductionin pituitary GnRH receptor content.

Type
Research Article
Information
Animal Production , Volume 49 , Issue 1 , August 1989 , pp. 95 - 102
Copyright
Copyright © British Society of Animal Science 1989

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References

REFERENCES

Belchetz, P.E., Plant, T. M., Nakir, Y., Keogh, E. J. and Knobil, E. 1978. Hypophysical responses to continuous and intermittent delivery of hypothalamic gonadotrophin releasing hormone.Science, Washington 202: 631–633.CrossRefGoogle Scholar
Cahill, L. P., Saumande, J., Ravault, J. P., Blanc, M., Thimonier, J., Mariana, J. C. and Mauleon, P. 1981. Hormonal and follicular relationships in ewes of high and low ovulation rate. Journal of Reproduction and Fertility 62: 141–150.CrossRefGoogle Scholar
Clarke, I. J., Burman, K. J., Doughton, B. W. and Cummins, J. T. 1986. Effectsof constantinfusion of gonadotrophin-releasing hormone in ovariectomized eweswith hypothalamo-pituitary disconnection: further evidence for differential control of LH and FSH secretion and the lack of a priming effect. Journal of Endocrinology 111: 43–49.CrossRefGoogle Scholar
Clarke, I. J. and Cummins, J. T. 1982. The temporal relationship between gonadotrophin releasing hormone (GnRH)and luteinizing hormone(LH) secretions in ovariectomised ewes. Journal of Endocrinology 111: 1737–1739.CrossRefGoogle Scholar
Foster, J. P. and Crighton, D. B. 1974. Luteinizing hormone (LH)release after single injections of synthetic LH-releasing hormone(LH-RH)in the ewe at three different reproductive stages and comparison with natural LH-release at oestrus. Theriogenology 2: 87–100.CrossRefGoogle ScholarPubMed
Glencross, R. G., Abeywardene, S. A., Corney, S. J. and Morris, H. S. 1981. The use of oestradiol-17β antiserum covalently coupled to sepharose to extract oestradiol-17β from biological fluids. Journal of Chromatography 2323: 193–197.CrossRefGoogle Scholar
Glencross, R. G. and Pope, G. S. 1981. Concentrations of oestradiol-17β and progesterone in the plasma of dairy heifers before and after cloprostenol-induced and natural luteolysis and during early pregnancy. Animal Reproduction Science 4: 93–106.CrossRefGoogle Scholar
Goodman, R. L., Pickover, S. M. and Karsch, F. J. 1981. Ovarian feedback control of follicle-stimulating hormone in the ewe: evidence for selective suppression Endocrinology 108: 772–777.CrossRefGoogle ScholarPubMed
Haresign, W. 1978. Ovulation control in the sheep. In Control of Ovulation (ed. Crighton, D. B.,Haynes, N. B., Foxcroft, G. R. and Lamming, G. E.), pp. 435–451. Butterworths,London.CrossRefGoogle Scholar
Khalid, M., Haresign, W. and Hunter, M. G. 1987. Pulsatile GnRH administration stimulates the number of pituitary GnRH receptors in seasonally anoestrous ewes. Journal of Reproduction and Fertility 79: 223–230.CrossRefGoogle ScholarPubMed
McLeod, B. J. and Haresign, W. 1984. Induction of fertile oestrus in seasonally anoestrous ewes with low doses of GnRH. Animal Reproduction Science 7: 413–420.CrossRefGoogle Scholar
McLeod, B. J., Haresign, W. and Lamming, G. E. 1982a. The induction of ovulation and luteal function in seasonally anoestrous ewes treated with small-dose multiple injections of GnRH. Journal of Reproduction and Fertility 65: 215–221.CrossRefGoogle ScholarPubMed
McLeod, B. J., Haresign, W. and Lamming, G. E. 1982b. Response of seasonally anoestrous ewes to small-dose multiple injections of GnRH with and without progesterone pretreatment. Journal of Reproduction and Fertility 65: 223–230.CrossRefGoogle ScholarPubMed
McLeod, B. J., Haresign, W. and Lamming, G. E. 1983. Induction of ovulation in seasonally anoestrous ewes by continuous infusion of low doses of GnRH. Journal of Reproduction and Fertility 68: 489–495.CrossRefGoogle ScholarPubMed
McNeilly, A. S. 1984. Changes in FSH and the pulsatile secretion of LH duringthe delay in oestrus induced by treatment of ewes with bovine follicular fluid. Journal of Reproduction and Fertility 72: 165–172.CrossRefGoogle Scholar
Nett, T. M., Crowder, M. E., Moss, G. E. and Duello, T. M. 1981. GnRH-receptor interaction v. down-regulation of pituitary receptors for GnRH in ovariectomized ewes by infusion of homologous hormone. Biology of Reproduction 24: 1145–1155.Google ScholarPubMed
Piper, E. L., Perkins, J. L., Tugwell, D. R. and Vaught, W. G. 1973. Effect of LRF infusions on LH secretion patterns. Journal of Animal Science 37: 324 (Abstr.).Google Scholar
Rippel, R. H., Johnson, E. S. and White, W. F. 1974. Effect of consecutive injections of synthetic gonadotropin releasing hormoneon LH release in the anestrous and ovariectomized ewe. Journal of Animal Science 39: 907–914.CrossRefGoogle ScholarPubMed
Smith, M. A., Perrin, M. H. and Vale, W. W. 1983. Desensitization of cultured pituitary cells to gonadotrophin-releasing hormone: evidence for a post-receptor mechanism. Molecular and Cellular Endocrinology 30: 85–96.CrossRefGoogle ScholarPubMed
Symons, A. M., Cunningham, N. F. and Saba, N. 1974. The gonadotrophic hormone response of anoestrous and cyclic ewes to synthetic luteinizing hormone-releasing hormone. Journalof Reproduction and Fertility 39: 11–21.CrossRefGoogle ScholarPubMed
Worthy, K., Haresign, W., Dodson, S., McLeod, B. J., Foxcroft, G. R., Haynes, N. B. 1985. Evidence that the onset of the breeding season in the ewe maybe independent of decreasing plasma prolactin concentrations. Journal of Reproduction and Fertility 75: 237–246.CrossRefGoogle Scholar