Plasma prolactin concentrations in non-pregnant mares at different times of the year and in relation to events in the cycle.
Abstract: Plasma prolactin concentrations were measured in mares using an homologous radioimmunoassay. An annual rhythm in plasma prolactin was found, with concentrations higher during the summer than during the winter. In addition to this seasonal pattern, occasional high concentrations of prolactin were seen when concentrations were otherwise basal. Blood samples taken from mares during an oestrous cycle in October-November showed that prolactin values were basal for most of the cycle, with a marked rise in prolactin shortly before the onset of oestrus. This prolactin peak was associated with an increase in the size of the largest follicle, and with a peak of PGFM in some mares, but did not appear to be related to the LH surge. In oestrous cycles in March and May-June, there was a wide variation in the baseline of prolactin secretion, in accordance with the seasonal pattern already mentioned. However, the peak of prolactin seen around oestrus in October-November was less obvious in March and May-June. Post-partum mares showed a high but irregular profile of prolactin concentrations with no clear-cut pattern in relation to the oestrous cycle.
Publication Date: 1987-01-01 PubMed ID: 3479582
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The research analyzes prolactin concentration in non-pregnant mares throughout different seasons and relates it to their reproductive cycle events.
Methodology and Scope
- The study takes into account plasma prolactin concentration in mares by utilizing a homologous radioimmunoassay.
- The concentration of prolactin was measured in different seasons, from summer to winter, to detect anyannual rhythms.
- The study examines the variation in prolactin levels during different stages of the mares’ oestrous cycle in various months such as October-November, March, and May-June.
- The study also reviews the prolactin concentration profiles in post-partum mares and its relation to the oestrous cycle.
Findings
- The researchers found a noticeable annual rhythm in plasma prolactin concentration, with increments in summer compared to winter.
- Besides this seasonal rhythm, sporadic surges in prolactin concentration were identified during otherwise basal times.
- In the oestrous cycle occurring in October-November, for the most part, the prolactin values remained basal with a substantial increase just before oestrus. This prolactin peak was associated with the rise in size of the largest follicle and a peak in PGFM in some of the mares.
- The LH surge didn’t seem to have a relation to the prolactin peak, as per the study.
- In the oestrous cycles of March and May-June, there were significant variations in the baseline prolactin secretion, following the seasonal pattern mentioned earlier. However, the prolactin peak around oestrus in October-November was lesser evident in the other tested months.
- Prolactin concentrations in post-partum mares portrayed an elevated but irregular trend with no discernible pattern in relation to the oestrous cycle.
Conclusions
- The research concludes with the detection of a seasonal rhythm in mares’ plasma prolactin concentration. This varied level of prolactin is also associated with various events in the mares’ reproductive cycle like oestrus, growth of the follicle, and PGFM peak, but not the LH surge.
- The prolactin concentration alters irregularly in post-partum mares, indicating possible diverse influences on prolactin secretion in this group.
Cite This Article
APA
Worthy K, Colquhoun K, Escreet R, Dunlop M, Renton JP, Douglas TA.
(1987).
Plasma prolactin concentrations in non-pregnant mares at different times of the year and in relation to events in the cycle.
J Reprod Fertil Suppl, 35, 269-276.
Publication
Researcher Affiliations
- Department of Veterinary Clinical Biochemistry, University of Glasgow Veterinary School, Garscube Estate, Bearsden, U.K.
MeSH Terms
- Animals
- Estrus / blood
- Female
- Horses / blood
- Postpartum Period / blood
- Pregnancy
- Progesterone / blood
- Prolactin / blood
- Seasons
Citations
This article has been cited 2 times.- Tortonese DJ. Intrapituitary mechanisms underlying the control of fertility: key players in seasonal breeding. Domest Anim Endocrinol 2016 Jul;56 Suppl(Suppl):S191-203.
- Kyvsgaard NC, Høier R, Brück I, Nansen P. Effect of two virus inactivation methods: electron beam irradiation and binary ethylenimine treatment on determination of reproductive hormones in equine plasma. Acta Vet Scand 1997;38(3):225-33.
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