Kinetics of gonadotrophins in the mare.
Abstract: Isoelectric focussing of crude extracts of equine pituitaries was used to obtain fractions containing FSH and LH. By comparison with FSH, LH was distributed over a similar but wider pH range indicating more marked polymorphism as determined from their isoelectric point (pI). Molecules with more sialic acid showed lower pI consistent with the concept that sialic acid is the major factor in determining pI and polymorphism in FSH and LH. Appropriate fractions were labelled with 125I, purified further and used in kinetic studies. FSH and LH molecules of similar pI had similar kinetics; however, LH molecules of high pI disappeared from plasma more rapidly. This is attributed to the role of sialic acid in preventing hormone degradation by non-target tissues, thus increasing the half-life and therefore the biological potency of the hormone. Since the form in which gonadotrophins circulate is not known, data are presented using 2 forms of LH and one of FSH. While this provides information from which most kinetic parameters may be determined, meaningful production rates cannot be calculated until the circulating form is identified. Other experiments on gonadotrophin kinetics are reviewed critically in the light of these findings.
Publication Date: 1979-01-01 PubMed ID: 289782
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- Journal Article
Summary
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The researchers’ work centers on the kinetic behavior of two hormones, FSH and LH, found in horse pituitary glands. The study particularly notes that the amount of sialic acid present in these hormones plays a significant role in their stability, lifespan, and biological effectiveness.
Methodology and Findings
- The study uses isoelectric focusing to obtain fractions of FSH and LH from horse pituitary extracts. Isoelectric focusing is a technique used to separate different proteins based on their isoelectric points, which is the pH at which the protein molecule carries no net electrical charge.
- This technique allowed the team to observe that LH had a wider pH range than FSH, suggestive of higher polymorphism. In biology, polymorphism refers to the occurrence of different forms among the members of a population or colony, or in the lifecycle of an individual organism.
- The molecules with increased amounts of sialic acid, a kind of sugar, showed a lower isoelectric point. This observation is congruent with the idea that the amount of sialic acid a hormone contains is a major factor in determining both its isoelectric point and its polymorphism.
Role of Sialic Acid in Hormone Activity
- For greater investigation, appropriate fractions of the hormones were labeled with iodine-125, a radioactive isotope used in medical imaging and radiation therapy. These were subsequently purified for kinetic studies.
- Both FSH and LH molecules with the same isoelectric point displayed similar kinetic activity.
- However, LH molecules with a high isoelectric point disappeared from plasma faster. Researchers attribute this to the role of sialic acid in shielding the hormone from degradation by non-target tissues. This shielding effect increases the half-life of the hormone, as well as its biological potency.
Limits of the Study and Future Research Needs
- The researchers acknowledge that the form in which these gonadotropins present in circulation is not currently known.
- To overcome this uncertainty, they presented their findings using two different forms of LH and one of FSH.
- While this helps determine some kinetic parameters, a meaningful calculation of production rates isn’t feasible until we understand the circulating form of these hormones.
- Lastly, they critically examine other research on gonadotropin kinetics within the context of this study’s revelations.
Cite This Article
APA
Irvine CH.
(1979).
Kinetics of gonadotrophins in the mare.
J Reprod Fertil Suppl(27), 131-141.
Publication
Researcher Affiliations
MeSH Terms
- Animals
- Estrus
- Female
- Follicle Stimulating Hormone / blood
- Follicle Stimulating Hormone / metabolism
- Horses / physiology
- Isoelectric Point
- Luteinizing Hormone / blood
- Luteinizing Hormone / metabolism
- Metabolic Clearance Rate
- Ovulation
- Pituitary Gland / metabolism
- Pregnancy
Citations
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