Testosterone secretion during early pregnancy in mares.
Abstract: We have characterized the testosterone secretion pattern during the first 80 d of pregnancy in mares and determined the sources that contribute to circulating testosterone levels during this period. Ten untreated, pregnant mares (Group 1), 10 altrenogest-treated, pregnant mares (Group 2), and 10 altrenogest-treated, pregnant mares in which the CL was eliminated by administration of PGF-2alpha on Day 16 (Group 3) were used in this study. Complete luteolysis occurred following PGF-2alpha administration in all mares in Group 3. Six of the 10 mares in Group 3 did not have an active CL until after Day 60 of pregnancy (Group 3a) and were included in the analysis. The remaining four mares developed a new CL on Days 32, 40, 43 and 49 of pregnancy and were excluded from analysis. Mares without a functional CL (Group 3a) had significantly lower testosterone concentrations than mares with a functional CL (Groups 1 and 2), during the period before equine chorionic gonadotropin (eCG) secretion. At the onset of eCG secretion, testosterone concentrations increased rapidly but the rate of increase decreased with time in mares with a functional CL (Groups 1 and 2). In mares without a functional CL (Group 3a), testosterone concentrations did not increase at the onset of eCG secretion but increased at a gradually increasing rate after Day 50. The lower testosterone concentration in mares without a functional CL before eCG secretion suggests that the CL contributes significantly to the circulating testosterone concentration during the period before eCG secretion. The close time relationship between the onset of eCG secretion and the increase in testosterone secretion in mares with a functional CL and the lack of a testosterone increase in pregnant mares without a functional CL suggest that the increase in testosterone secretion after Day 35 of pregnancy is the result of eCG-stimulated, luteal testosterone synthesis.
Publication Date: 1996-04-15 PubMed ID: 16727877DOI: 10.1016/0093-691x(96)00076-3Google Scholar: Lookup
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- Journal Article
Summary
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This research article explores how testosterone is secreted during the first 80 days of a horse’s pregnancy. They found that the loss of the corpus luteum, an organ that plays a vital role in pregnancy, leads to significantly lower testosterone levels until the onset of equine chorionic gonadotropin (eCG) secretion, a hormone produced during pregnancy.
Research Methodology
- The research involved 30 pregnant mares across three different groups: untreated, treated with a drug called altrenogest, and a group treated with altrenogest and PGF-2alpha to eliminate the corpus luteum (CL).
- The corpus luteum was successfully removed in all mares from the third group. Six of these mares did not have an active CL until after the 60th day of pregnancy and were included in the analysis. The other four developed a new CL during the course of pregnancy and were excluded from results analyses.
Findings
- Mares without a functional corpus luteum (group 3a) had significantly lower testosterone concentrations, suggesting the CL plays a significant role in circulating testosterone levels before the secretion of eCG.
- Once the eCG began to secrete, testosterone levels dramatically increased in mares with a functional corpus luteum (groups 1 and 2), though the rate of increase slowed over time.
- In mares without a functional CL (group 3a), testosterone levels didn’t increase at the onset of eCG secretion but did gradually increase after the 50th day of pregnancy.
Conclusion
- The study concludes that the CL significantly contributes to circulating testosterone levels before the secretion of eCG. It also posits that testosterone secretion after the 35th day of pregnancy results from eCG stimulating luteal testosterone synthesis.
- The research deepens understanding of testosterone patterns during horse pregnancies, which could potentially inform strategies for managing pregnancy in horses.
Cite This Article
APA
Daels PF, Chang GC, Hansen B, Mohammed HO.
(1996).
Testosterone secretion during early pregnancy in mares.
Theriogenology, 45(6), 1211-1219.
https://doi.org/10.1016/0093-691x(96)00076-3 Publication
Researcher Affiliations
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA. pfd1@cornell.edu
Citations
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