Hemodynamics of the corpus luteum in mares during experimentally impaired luteogenesis and partial luteolysis.

The researchers aimed to investigate the impact of luteal disturbances on the blood flow and concentration of certain hormones in mares during their early and middle diestrus stage.

Objectives and Methodology

• The study aimed to analyze how luteal disturbances in horses (mares) during the early and mid-diestrus stages impacted luteal vascularity (blood supply to luteal cells) and the plasma concentrations of progesterone (P4), prolactin (PRL), and 13,14-dihydro-15-keto-PGF (PGFM).
• The study involved two experiments, both of which involved the treatment of 21 mares on two different days following their ovulation.
• The first experiment involved treatment two days post-ovulation, and the second involved treatment eight days post-ovulation.
• In both the experiments, the mares were treated with either 2 mL of 0.9% NaCl, 1 mg Dinoprost, or 10 mg Dinoprost. The Dinoprost dosages were intended to simulate luteal disturbances.

Results

• In the first experiment, the PGF-D2 and 1/10PGF-D2 groups had a lower increase of plasma concentration of P4 until H48 and reduced maximum P4 concentrations on D8-D11 than mares from the Control-D2 group.
• However, no differences among the groups were detected for luteal vascularity during early and mid-diestrus.
• In the second experiment, it was found that complete and partial luteolysis occured in mares from the PGF-D8 and 1/10PGF-D8 groups, respectively. This means that the corpus luteum (CL), a hormone-secreting structure in mammals, was either completely or partially degraded in these mares.
• Potentially regressed CLs (from the 1/10PGF-D8 group) generated more Doppler signals than completely regressed CLs (from the PGF-D8 group) between D10 and D13, indicating more blood flow in the partially regressed CLs.
• In both the experiments, a transient increase in PRL activity was observed parallel to the PGFM pulse in mares receiving 1 or 10 mg Dinoprost, indicating that these treatments resulted in a temporary rise in the secretion of PRL, a hormone with key roles in reproductive processes.

Conclusion

• The use of prostaglandin on D2 at either a conventional dose or one-tenth of the dose impaired the development of luteal cells in mares.
• The lower dose of prostaglandin led to a partial regression of mature CLs.
• The blood supply was reduced in partially regressed CLs, but not in CLs undergoing impaired luteogenesis. This suggests a possible correlation between luteal disturbances and changes in the blood supply to luteal cells.