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Secretory patterns and rates of gonadotropin-releasing hormone, follicle-stimulating hormone, and luteinizing hormone revealed by intensive sampling of pituitary venous blood in the luteal phase mare.
Abstract: We used our unique nonsurgical technique for collecting pituitary venous (pit) blood to study GnRH, FSH, and LH secretion patterns in midluteal phase mares. This method does not perturb endocrine function and allows continuous monitoring of GnRH and gonadotropin (Gn) secretion, determination of the amount of GnRH perfusing gonadotropes, and direct measurements of the amounts of Gn secreted. In a total of 80 h of 5-min sampling in four mares, eight Gn peaks occurred; however, more frequent sampling was needed to define secretory events precisely. Therefore, pit blood was collected continuously and split into 30-sec segments in six mares. To ensure a peak during sampling, the opioid antagonist naloxone was given after 4-6 h of sampling to try to replicate a physiological signal for GnRH release. Naloxone induced Gn peaks in jugular blood that were indistinguishable in amplitude from spontaneous peaks. Intensive sampling of pit blood showed that jugular peaks reflected major episodes of GnRH and Gn secretion lasting 30-55 min, which were similar in profile whether naloxone induced or spontaneous and consisted of a train of three to six peaks of diminishing amplitude. Peaks of GnRH and, less often, Gn also occurred outside major episodes. Despite markedly variable size, GnRH peak maxima were correlated with the amount of LH and FSH secreted in concurrent peaks. Likewise, cross-correlation analyses (n = 960 samples/mare) showed close correspondence between patterns of GnRH and secreted FSH and LH. The delay (+/- SEM) between GnRH and Gn maxima was 0.62 +/- 0.18 min for LH and 0.18 +/- 0.22 min for FSH. The majority of GnRH and Gn peaks were concurrent; however, 34.7% of GnRH peaks occurred without Gn peaks. These peaks had a lower amplitude than those with Gn peaks (P 1.5) continued at a low level for 40 +/- 9% (LH) or 64 +/- 14% (FSH) of the time between Cluster-defined peaks during the basal period. We conclude that in the luteal phase 1) the predominant mode of GnRH and Gn secretion is as concurrent, large amplitude, prolonged episodes that appeared to be the summation of a train of peaks; and 2) a GnRH dose-Gn response relationship operates endogenously. This along with the synchronicity of secretion patterns of the three hormones suggest that GnRH is the major secretagogue for both LH and FSH.
Publication Date: 1993-01-01 PubMed ID: 8419124DOI: 10.1210/endo.132.1.8419124Google Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
- Research Support
- U.S. Gov't
- P.H.S.
Summary
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The research article “Secretory patterns and rates of gonadotropin-releasing hormone, follicle-stimulating hormone, and luteinizing hormone revealed by intensive sampling of pituitary venous blood in the luteal phase mare” discusses the secretion patterns of certain hormones in mares during the midluteal phase, providing evidence that Gonadotropin-Releasing Hormone (GnRH) significantly influences the secretion of Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH).
Research Methodology
- The researchers utilized their proprietary non-surgical technique for collecting pituitary venous blood from mares. This method does not disturb endocrine function and allows consistent monitoring of GnRH and gonadotropin secretion.
- In a total of 80 hours of 5-minute sampling from four mares, they observed eight peaks of gonadotropin. However, they found more frequent sampling necessary for precise definition of secretory events.
- To ensure the presence of a peak during sampling, the researchers administered the opioid antagonist naloxone after 4 to 6 hours of sampling. Naloxone induced hormone peaks comparable in amplitude to spontaneous peaks.
- They noted that intensive pituitary blood sampling revealed that jugular peaks were indicative of significant episodes of GnRH and gonadotropin (Gn) secretion, which lasted 30-55 minutes.
Findings
- Sampling revealed that the majority of GnRH and Gn secretion occurred concurrently, with larger amplitude, prolonged episodes appearing to be a summation of a series of peaks.
- They also found that despite having a markedly variable size, maxima of GnRH peaks correlated with the amount of LH and FSH secreted in simultaneous peaks.
- It was determined that a delay existed between peaks of GnRH and Gn maxima – 0.62 +/- 0.18 minutes for LH and 0.18 +/- 0.22 minutes for FSH.
- Approximately 34.7% of GnRH peaks occurred without corresponding Gn peaks. These GnRH peaks had a lower amplitude than those with Gn peaks.
- Continuous hormone secretion occurred at a low level for 40 +/- 9% (LH) or 64 +/- 14% (FSH) of the time between the key peaks during the basal period.
Conclusion
- The research concluded that in the luteal phase, GnRH and Gn are predominantly secreted concurrently, as higher amplitude, prolonged episodes.
- They identified a GnRH dose-Gn response relationship endogenously present, suggesting that GnRH is the main secretagogue for both LH and FSH.
Cite This Article
APA
Irvine CH, Alexander SL.
(1993).
Secretory patterns and rates of gonadotropin-releasing hormone, follicle-stimulating hormone, and luteinizing hormone revealed by intensive sampling of pituitary venous blood in the luteal phase mare.
Endocrinology, 132(1), 212-218.
https://doi.org/10.1210/endo.132.1.8419124 Publication
Researcher Affiliations
- Animal and Veterinary Sciences Group, Lincoln University, Canterbury, New Zealand.
MeSH Terms
- Animals
- Estrus / physiology
- Female
- Follicle Stimulating Hormone / blood
- Follicle Stimulating Hormone / metabolism
- Gonadotropin-Releasing Hormone / blood
- Gonadotropin-Releasing Hormone / metabolism
- Horses / blood
- Kinetics
- Luteinizing Hormone / blood
- Luteinizing Hormone / metabolism
- Naloxone / pharmacology
- Pituitary Gland / blood supply
- Veins
Grant Funding
- DK-38322 / NIDDK NIH HHS
Citations
This article has been cited 3 times.- Fanelli D, Tesi M, Rota A, Beltramo M, Conte G, Giorgi M, Barsotti G, Camillo F, Panzani D. hCG is more effective than the GnRH agonist buserelin for inducing the first ovulation of the breeding season in mares. Equine Vet J 2022 Mar;54(2):306-311.
- Maruska KP, Levavi-Sivan B, Biran J, Fernald RD. Plasticity of the reproductive axis caused by social status change in an african cichlid fish: I. Pituitary gonadotropins. Endocrinology 2011 Jan;152(1):281-90.
- Midgley AR Jr, McFadden K, Ghazzi M, Karsch FJ, Brown MB, Mauger DT, Padmanabhan V. Nonclassical secretory dynamics of LH revealed by hypothalamo-hypophyseal portal sampling of sheep. Endocrine 1997 Apr;6(2):133-43.
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