Relaxin activity in foaling mares.
Abstract: Plasma relaxin concentrations were measured hourly by radio immunoassay in 4 pregnant mares from 11 days before until 4 days after natural foaling. Pre-partum levels ranged from 4 to 7 ng/ml without any surge until the second stage of labour when they increased rapidly to about 11 ng/ml. In 3 of these mares, relaxin activity declined immediately after the expulsion of the placenta and was below detectable levels within 36 h. In the other mare relaxin activity did not fall until after the mechanical removal of the placenta 7 h after foaling. Eight mares were induced to foal by the administration of oxytocin. In 5 out of 6 mares induced with a single i.v. injection of 40 i.u. plasma relaxin increased following injection and peaked at 17 ng/ml shortly after foaling and expulsion of placenta. Activity then rapidly declined. In the 6th mare, which retained the placenta, relaxin activity did not decrease after foaling. Administration of more oxytocin to this mare after foaling resulted in a further increase in plasma relaxin activity, but oxytocin treatment of other mares after placental delivery failed to elicit a similar increase. In the 7th mare 2 i.v. injections of 40 i.u. oxytocin induced a relaxin concentration of 34 ng/ml whereas in the remaining mare one i.m. injection of 40 i.u. oxytocin led to a relaxin profile similar to that in naturally foaling mares. Oxytocin may therefore be responsible for the increased secretion rate of relaxin at foaling. These data support the concept that the placenta is the sole significant source of relaxin in the pregnant mare.
Publication Date: 1982-01-01 PubMed ID: 6962902
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The research discusses the secretion of relaxin hormone in mares during foaling and how it can potentially be influenced by the administration of oxytocin. The study finds that the rate of relaxin secretion increases during labor and suggests that the placenta is the main source of relaxin during pregnancy.
Research Setup
- The research was conducted on eight pregnant mares. The relaxin hormone concentration in their plasma was measured from 11 days pre-partum to 4 days post-partum. This hormone level was measured hourly using radioimmunoassay, a method to measure the intensity of biological substances.
- The research also included the administration of oxytocin to induce labor in these mares and observed the subsequent effects on relaxin hormone levels.
Findings
- Pre-partum relaxin levels ranged from 4 to 7 ng/ml and did not surge until the second stage of labor, where the levels increased rapidly to around 11 ng/ml.
- In three out of four mares, the relaxin activity declined immediately after placenta expulsion and fell below detectable levels within 36 hours.
- In one mare, the relaxin activity did not decline until after the mechanical removal of the placenta 7 hours after foaling, suggesting the placenta might play an essential role in relaxin secretion.
- Out of six mares that were induced to foal through a single i.v. injection of 40 i.u. oxytocin, five showed an increase in relaxin concentration following the injection, peaking at 17 ng/ml after the expulsion of the placenta. The relaxin levels then declined rapidly.
- The sixth mare, which retained the placenta, did not show a decrease in relaxin activity after foaling. Moreover, using additional oxytocin post-foaling led to an increase in relaxin activity.
- Such an increase in relaxin activity was not observed in other mares post-placental delivery, post-oxytocin treatment suggesting a link between the placenta and relaxin activity.
- Administration of oxytocin seemed to replicate the relaxin profile observed in naturally foaling mares thereby suggesting a possible role of oxytocin in increasing the secretion rate of relaxin at foaling.
Conclusion
- These findings support the idea that the placenta is the primary source of relaxin in pregnant mares, and the secretion rate of this hormone increases during labor.
- The role of oxytocin in influencing the secretion of relaxin at foaling was also intimated through this research.
Cite This Article
APA
Stewart DR, Stabenfeldt GH, Hughes JP.
(1982).
Relaxin activity in foaling mares.
J Reprod Fertil Suppl, 32, 603-609.
Publication
Researcher Affiliations
MeSH Terms
- Animals
- Female
- Horses / blood
- Kinetics
- Labor, Obstetric
- Pregnancy
- Pregnancy, Animal
- Radioimmunoassay
- Relaxin / blood
Citations
This article has been cited 1 times.- Cummins C, Carrington S, Fitzpatrick E, Duggan V. Ascending placentitis in the mare: A review. Ir Vet J 2008 May 1;61(5):307-13.
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