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No evidence for pituitary priming to gonadotropin-releasing hormone in relation to luteinizing hormone (LH) secretion prior to the preovulatory LH surge in ewes.
Biol Reprod. 2004 Jul; 71(1):224-35.BR

Abstract

The purpose of this study was to determine the occurrence of and the regulatory mechanisms involved in priming of the pituitary to GnRH before the preovulatory LH surge in sheep. Experiment 1: Forty-two ewes had progestagen devices removed after 14 days and were assigned to luteal (Lut) or follicular (Foll) groups. Fifteen days later, blood sampling was initiated either immediately or 36 h after induced luteolysis in groups Lut and Foll, respectively. After 4 h, ewes were administered either saline (n = 5) or 250 ng (n = 8) or 10 microg (n = 8) of GnRH. Five ewes per treatment group were killed 1 h later, while remaining animals were blood sampled for a further 7 h. Experiment 2: Eighteen ewes were allocated to Lut and Foll groups (described above). Blood samples were collected from 2 h before GnRH (10 microg) treatment until 7 h after. Despite up-regulated GnRH-R mRNA levels in Foll ewes, pituitary content and plasma levels of LH and LHbeta mRNA levels were similar between groups. Mean FSHbeta mRNA and plasma FSH levels were elevated in Lut ewes but declined after GnRH treatment. Inversely, plasma estradiol and inhibin-A concentrations were higher in Foll ewes and declined after GnRH treatment. Fewer LH(+ve)/secretogranin II(-ve) (SgII(-ve)) granules were present in gonadotropes of Foll ewes, coincident with increased basal LH levels. Fewer smaller sized granules were present after GnRH treatment. In conclusion, there was no evidence of self-priming before onset of the preovulatory LH surge. Constitutive release of LH(+ve)/SgII(-ve) granules may maintain basal LH levels while smaller sized, presumably mature granules may be preferentially released after GnRH stimulation.

Authors+Show Affiliations

Human Reproductive Sciences Unit, Medical Research Council, University of Edinburgh Centre for Reproductive Biology, Edinburgh EH16 4SB, United Kingdom. janet.crawford@agresearch.co.nzNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

15031142

Citation

Crawford, J L., et al. "No Evidence for Pituitary Priming to Gonadotropin-releasing Hormone in Relation to Luteinizing Hormone (LH) Secretion Prior to the Preovulatory LH Surge in Ewes." Biology of Reproduction, vol. 71, no. 1, 2004, pp. 224-35.
Crawford JL, McNeilly JR, McNeilly AS. No evidence for pituitary priming to gonadotropin-releasing hormone in relation to luteinizing hormone (LH) secretion prior to the preovulatory LH surge in ewes. Biol Reprod. 2004;71(1):224-35.
Crawford, J. L., McNeilly, J. R., & McNeilly, A. S. (2004). No evidence for pituitary priming to gonadotropin-releasing hormone in relation to luteinizing hormone (LH) secretion prior to the preovulatory LH surge in ewes. Biology of Reproduction, 71(1), 224-35.
Crawford JL, McNeilly JR, McNeilly AS. No Evidence for Pituitary Priming to Gonadotropin-releasing Hormone in Relation to Luteinizing Hormone (LH) Secretion Prior to the Preovulatory LH Surge in Ewes. Biol Reprod. 2004;71(1):224-35. PubMed PMID: 15031142.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - No evidence for pituitary priming to gonadotropin-releasing hormone in relation to luteinizing hormone (LH) secretion prior to the preovulatory LH surge in ewes. AU - Crawford,J L, AU - McNeilly,J R, AU - McNeilly,A S, Y1 - 2004/03/17/ PY - 2004/3/20/pubmed PY - 2005/1/6/medline PY - 2004/3/20/entrez SP - 224 EP - 35 JF - Biology of reproduction JO - Biol Reprod VL - 71 IS - 1 N2 - The purpose of this study was to determine the occurrence of and the regulatory mechanisms involved in priming of the pituitary to GnRH before the preovulatory LH surge in sheep. Experiment 1: Forty-two ewes had progestagen devices removed after 14 days and were assigned to luteal (Lut) or follicular (Foll) groups. Fifteen days later, blood sampling was initiated either immediately or 36 h after induced luteolysis in groups Lut and Foll, respectively. After 4 h, ewes were administered either saline (n = 5) or 250 ng (n = 8) or 10 microg (n = 8) of GnRH. Five ewes per treatment group were killed 1 h later, while remaining animals were blood sampled for a further 7 h. Experiment 2: Eighteen ewes were allocated to Lut and Foll groups (described above). Blood samples were collected from 2 h before GnRH (10 microg) treatment until 7 h after. Despite up-regulated GnRH-R mRNA levels in Foll ewes, pituitary content and plasma levels of LH and LHbeta mRNA levels were similar between groups. Mean FSHbeta mRNA and plasma FSH levels were elevated in Lut ewes but declined after GnRH treatment. Inversely, plasma estradiol and inhibin-A concentrations were higher in Foll ewes and declined after GnRH treatment. Fewer LH(+ve)/secretogranin II(-ve) (SgII(-ve)) granules were present in gonadotropes of Foll ewes, coincident with increased basal LH levels. Fewer smaller sized granules were present after GnRH treatment. In conclusion, there was no evidence of self-priming before onset of the preovulatory LH surge. Constitutive release of LH(+ve)/SgII(-ve) granules may maintain basal LH levels while smaller sized, presumably mature granules may be preferentially released after GnRH stimulation. SN - 0006-3363 UR - https://www.unboundmedicine.com/medline/citation/15031142/No_evidence_for_pituitary_priming_to_gonadotropin_releasing_hormone_in_relation_to_luteinizing_hormone__LH__secretion_prior_to_the_preovulatory_LH_surge_in_ewes_ L2 - https://academic.oup.com/biolreprod/article-lookup/doi/10.1095/biolreprod.104.027615 DB - PRIME DP - Unbound Medicine ER -