Kinetic studies and production rate of melatonin in pony mares.

The research study examines the kinetic parameters and the daily production rate of melatonin – the hormone that manages sleep-wake patterns, in horses. The study suggests that to affect a horse’s reproductive pattern through oral administration, the dose of melatonin required would need to be 10 times higher than the level produced at night by the horse.

Objective of the Research

• The aim of this study was to determine the kinetic parameters like plasma melatonin clearance and volume distribution, and the daily (nycthemeral) production rate of the hormone melatonin in pony mares. Kinetic parameters tell us how the horse’s body absorbs, distributes, metabolizes, and excretes melatonin.

Methodology

• The researchers conducted studies on twelve pony mares. Basic kinetic studies involved seven mares, while production rate studies were carried out on five others, under both long and short day conditions.
• Melatonin was administered through several means including intravenous (directly into the bloodstream), oral, and intragastric (directly into the stomach) routes at various dose levels, to understand the differences in absorption and effect.

Findings

• The study determined the plasma melatonin clearance rate — the body’s ability to eliminate melatonin from the blood — to be 1.02 +/- 0.31 l.kg-1.h-1, and the volume of distribution to be 0.89 +/- 0.53 L/kg for the 0.4 microgram/kg melatonin dose. The volume of distribution represents how well the melatonin is distributed throughout the body
• The systemic availability of melatonin — the portion of the administered melatonin dose that reaches the bloodstream — after oral and intragastric administration was consistently low (less or equal to 10%). This implies that most of the orally administered melatonin is metabolized before it can exert its physiological effects.
• The hourly melatonin production during short nights (36 +/- 33.6 ng.kg-1.h-1) and long nights (42 +/- 24.0 ng.kg-1.h-1) was not significantly different.

Conclusion

• Based on the study’s findings, it is concluded that to manipulate the reproductive pattern in horses, the oral dose of exogenous melatonin (melatonin originating outside the organism) required would need to be 10 times higher than the nocturnal melatonin production to ensure a physiological plasma melatonin concentration.