Hyperleptinemia in horses: responses to administration of a small dose of lipopolysaccharide endotoxin in mares and geldings.

The research examines the impact of high leptin levels (hyperleptinemia) on the hormonal and hematologic systems of horses, specifically mares and geldings, after they were subjected to a dose of lipopolysaccharide endotoxin. The results suggest that hyperleptinemia has a minimal influence on these systems.

Selection of Subjects

• The study involved 8 mares and 8 geldings in good body condition, half of which had hyperleptinemia, while the other half had normal leptin concentrations.

Administration of Endotoxin

• The horses were administered Escherichia coli O55:B5 endotoxin or saline only, in a single-switchback design, where the horses and the treatments were randomly assigned for the first infusion.
• The physiological variables and blood components were monitored for 24 hours after the onset of the infusions. The roles were switched and the second infusions were given 8 days later.

Findings

• The endotoxin infusion was found to have increased the rectal temperature, heart rate, respiration rate, plasma total protein concentration, and blood packed cell volume of the horses.
• The blood levels of leukocytes, lymphocytes, and neutrophils – types of white blood cells – decreased after the infusion.
• The study also observed that blood platelet concentration was influenced by an interaction between the sex and the leptin status of the horses.

Leptin Concentration

• Regardless of whether the horses had hyperleptinemia or normal leptin levels, the administration of endotoxin resulted in increased plasma leptin concentrations.

Cortisol and Prolactin Concentration

• There were noticeable interactions of sex with endotoxin treatment and time for plasma concentrations of cortisol – stress hormone – and prolactin, a hormone that plays important roles in reproduction.
• However, the concentrations of the growth hormone (GH) were impacted only by the time after infusion.

Conclusion

• In spite of the physiological changes triggered by endotoxin, the effects of hyperleptinemia were considered minor, indicating that this condition, which is associated with symptoms of type-2 diabetes, has an insignificant influence on the hematologic and hormonal systems under study.