Stimulatory effect of PGF2α on PRL based on experimental inhibition of each hormone in mares

Area of Science:

• Reproductive Endocrinology
• Veterinary Physiology
• Equine Reproduction

Background:

• Synchronous peaks of prostaglandin F2α metabolite (PGFM) and prolactin (PRL) occur during the luteolytic period in mares.
• The causal relationship between PGFM and PRL during this period remains unclear.

Purpose of the Study:

• To determine if prostaglandin F2α (PGF2α) affects prolactin (PRL) secretion or vice versa in mares.
• To investigate the influence of PGF2α inhibition on PRL levels and PRL inhibition on PGF2α metabolite (PGFM) levels.

Main Methods:

• mares were treated with flunixin meglumine (to inhibit PGF2α) or bromocriptine (to inhibit PRL) at 14 days post-ovulation.
• Blood samples were collected hourly for 10 hours post-treatment.
• Concentrations of PGFM and PRL were measured and compared between treatment groups and controls across June and September.

Main Results:

• Flunixin meglumine treatment significantly reduced PGFM concentrations, indicating successful PGF2α inhibition.
• Bromocriptine treatment did not affect PGFM concentrations.
• Both flunixin meglumine and bromocriptine treatments reduced PRL concentrations compared to controls; PRL levels were significantly lower in September than in June.

Conclusions:

• Results support the hypothesis that PGF2α positively influences PRL secretion in mares.
• The observed synchrony between PGFM and PRL pulses is likely due to PGF2α acting on PRL, not the reverse.
• Seasonal variations in PRL concentrations were observed, with lower levels in September compared to June.