Release of LH, FSH and GnRH into pituitary venous blood in mares treated with a PGF analogue, luprostiol, during the transition period.

The study investigated the release of hormones LH, FSH, and GnRH in horses after being treated with the drug luprostiol. Through a series of blood samples taken at varying intervals, treatment was found to increase hormone levels, with certain hormones peaking before others.

Methodology

• The study was conducted on 9 horses. Some were fitted with cannulae (tubes insertable into the body) in two positions – the intercavernous sinus (in the pituitary gland area) and the jugular vein, while others only had jugular cannulae.
• Four of the horses with only jugular cannulae and three with cannula in both positions were given 7.5 mg of luprostiol through intramuscular injection. One horse fitted with cannulae in both positions received a 3.75 mg luprostiol intravenous dosage.
• Blood samples were collected before and after treatment at varying intervals (2-, 5- or 10-minutes) to analyze the concentration of the hormones LH, FSH, and GnRH.

Findings

• The treatment caused an immediate and significant increase of LH and FSH hormones in both ICS and jugular blood samples within 2-10 minutes.
• The hormone peaks in the ICS samples occurred earlier and showed up to 100 times higher levels of LH.
• GnRH levels in the ICS samples only consistently increased after LH and FSH had reached their peak levels.
• In both types of samples, elevated levels of LH and FSH were present for 60-120 minutes after treatment, but returned to their baseline levels by 240 minutes.
• In control group of untouched horses, continuous sampling revealed no pulses of LH or FSH in 3 individuals, and only one pulse, which was preceded by small rises of GnRH, per day in 2 horses.

Conclusion

• This study provides evidence of a rapid hormonal response in horses, specifically an increase in LH, FSH, and GnRH levels, following treatment with the drug luprostiol. The varying onset and duration of these peaks suggest differential timing in the hormonal response.
• These findings could have implications on biomedical applications involving the regulation of these hormones in horses, potentially leading to more effective treatment strategies and understanding of horse physiology.