Secretion rates and short-term patterns of gonadotrophin-releasing hormone, FSH and LH throughout the periovulatory period in the mare.
Abstract: We have developed a non-surgical technique for long-term collection of pituitary venous blood which consists of slightly diluted hypophysial portal blood into which pituitary hormones have been secreted. In these experiments jugular and pituitary venous blood samples were collected from five unmedicated, ambulatory mares at 5-min intervals for 2-6 h on 11 occasions during the 6 days surrounding the ovulatory LH peak. Jugular blood only was collected from another five periovulatory mares without pituitary cannulae. The duration of oestrus was similar in mares with and without pituitary cannulae and all mares ovulated, showing that the procedure did not affect the reproductive axis. In all pituitary-cannulated mares the secretion of gonadotrophin-releasing hormone (GnRH), FSH and LH occurred almost continuously with broad, concurrent pulses of the three hormones superimposed upon this tonic background. Only 9% of the GnRH pulses appeared to be ineffective in inducing a rise in gonadotrophin levels. When measured in pituitary blood, gonadotrophin pulse frequency varied from 0.45 pulses/h early in the LH surge to 1.87 pulses/h at the time of ovulation. In contrast, mean pulse frequency measured in jugular blood did not exceed 1 pulse/h throughout the periovulatory period in cannulated or non-cannulated mares. The low amplitude of jugular pulses (less than 50% fractional increase) may have caused problems in identifying the pulses. In the two mares in which pituitary venous blood was sampled during more than one period before ovulation, GnRH secretion tended to be lower on the day of ovulation (day 0) than earlier in oestrus (ratio day 0:day -1; mare WV = 0.58, mare LS = 0.66), whereas LH secretion rate was higher on the day of ovulation (ratio day 0:day -1; mare WV = 1.54, mare LS = 6.68). These studies show that the painless and non-invasive collection of pituitary venous blood, which is possible only in horses, can provide a useful tool for studying hypothalamic-pituitary interactions under completely physiological conditions.
Publication Date: 1987-09-01 PubMed ID: 3117955DOI: 10.1677/joe.0.1140351Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This research was about understanding the secretion rates and patterns of gonadotrophin-releasing hormone, FSH and LH hormones during the periovulatory period in mares, using a non-invasive procedure to collect pituitary venous blood.
Methodology and Sampling
- The researchers developed a non-surgical technique for the collection of pituitary venous blood, which is composed of slightly diluted hypophysial portal blood. This blood is infused with hormones secreted from the pituitary gland.
- Experiments were conducted on five mares free of medication, from which both jugular and pituitary venous blood samples were collected. These samples were drawn at 5-minute intervals for periods ranging from 2 to 6 hours. This was done on eleven occasions over six days surrounding an ovulatory LH (Luteinizing Hormone) peak.
- Another five mares, also in the periovulatory period but without pituitary cannulae, were used solely for jugular blood collection. The duration of oestrus, or the reproductive phase where the mare is receptive to mating, was shown to have remained unchanged for mares with and without pituitary cannulae. Furthermore, all mares ovulated, indicating that the procedure did not impact the reproductive process.
Findings and Observations
- In the mares with the pituitary cannulae, the three hormones GnRH (Gonadotrophin-releasing hormone), FSH (Follicle-stimulating hormone) and LH, were found to be released almost continuously. This release also displayed broad, simultaneous pulses of these hormones, which were superimposed over the continuous ‘tonic’ background secretion.
- Only nine percent of the GnRH pulses did not succeed in inducing a quantifiable rise in gonadotrophin levels. Recorded pulse frequency for this hormone ranged from 0.45 pulses per hour early in the LH surge to 1.87 pulses per hour near the time of ovulation, when measured in pituitary blood.
- However, mean pulse frequency measured in jugular blood did not manifest more than 1 pulse per hour throughout the periovulatory period, both in mares with or without pituitary cannulae.
- In instances where pituitary venous blood sampling was conducted on more than one occasion before ovulation, it was observed that GnRH secretion was lower on the day of ovulation compared to earlier in oestrus. Conversely, LH secretion rate was higher on the day of ovulation.
Conclusion
- The research demonstrated the effectiveness of non-invasive and non-painful collection of pituitary venous blood. This procedure, apparently only feasible in horses, proved to be a useful tool for studying the interactions between the hypothalamus and pituitary gland under natural physiological conditions.
Cite This Article
APA
Alexander SL, Irvine CH.
(1987).
Secretion rates and short-term patterns of gonadotrophin-releasing hormone, FSH and LH throughout the periovulatory period in the mare.
J Endocrinol, 114(3), 351-362.
https://doi.org/10.1677/joe.0.1140351 Publication
Researcher Affiliations
- Veterinary Science Department, Lincoln College, Canterbury, New Zealand.
MeSH Terms
- Animals
- Blood Specimen Collection / veterinary
- Female
- Follicle Stimulating Hormone / blood
- Horses / physiology
- Jugular Veins
- Luteinizing Hormone / blood
- Ovulation
- Pituitary Gland / blood supply
- Pituitary Hormone-Releasing Hormones / blood
- Veins
Citations
This article has been cited 4 times.- Okada CTC, Kaps M, Perez Quesada J, Gautier C, Aurich J, Aurich C. Diestrous Ovulations in Pregnant Mares as a Response to Low Early Postovulatory Progestogen Concentration. Animals (Basel) 2020 Nov 30;10(12).
- Grant AD, Wilsterman K, Smarr BL, Kriegsfeld LJ. Evidence for a Coupled Oscillator Model of Endocrine Ultradian Rhythms. J Biol Rhythms 2018 Oct;33(5):475-496.
- 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.
- Veldhuis JD. Neuroendocrine mechanisms mediating awakening of the human gonadotropic axis in puberty. Pediatr Nephrol 1996 Jun;10(3):304-17.
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