The effect of long-term oral L-carnitine administration on insulin sensitivity, glucose disposal, plasma concentrations of leptin and acylcarnitines, and urinary acylcarnitine excretion in warmblood horses.

The study explores the impact of long-term L-carnitine intake on factors like insulin sensitivity, glucose usage, leptin levels, and acylcarnitine levels in horses. However, despite expectations, the results suggest there was no impact on insulin sensitivity, but rather increases leptin and acylcarnitine levels in horses.

Research Methodology

• The study was conducted using six 3-year-old warmblood geldings (male horses).
• A systematic experimental setup called a “double blind 2 × 2 Latin square design” was used. In this setup, neither the experimenter nor the horses were aware of which treatment they were receiving, in order to reduce bias.
• The horses were given 100 mg of L-carnitine per kg of body weight per day for 28 days and the effects were observed.
• The euglycemic-hyperinsulinemic clamp technique was used to measure glucose disposal and insulin sensitivity. This technique involves infusing insulin and glucose into the blood and measuring the amount of glucose needed to maintain blood sugar level, which helps estimate insulin sensitivity.
• The concentrations of leptin and insulin in the blood were calculated using Radioimmunoassays – a technique used to measure the concentration of specific proteins.
• Electrospray tandem mass spectrometry was used to evaluate acylcarnitines in both plasma and urine – a method used to rapidly and precisely measure small molecules.
• A statistical technique known as linear mixed-effects models was used to analyze the data. This model is used in experiments with repeated measures where data can be correlated.

Study Findings

• The finding was that long-term administration of L-carnitine did not have an effect on insulin sensitivity. That is, the ability of the horses’ cells to absorb and use glucose did not improve with the administration of L-carnitine.
• However, L-carnitine administration led to a significant increase in the plasma leptin concentration. This suggests that L-carnitine may influence the fat metabolism because leptin is a hormone predominantly made by adipose cells and enterocytes in the small intestine that helps to regulate energy balance by inhibiting hunger.
• The concentrations of free carnitine and short-chain acylcarnitines in plasma and urine also significantly increased. This could mean more fats were broken down to energy, because carnitine plays a crucial role in the breakdown of fat for energy.

Conclusion and Future Directions

• Despite the findings, the researchers feel that further studies on L-carnitine are necessary. This belief comes from the positive influence of L-carnitine on leptin and acylcarnitine, which could potentially be beneficial in treating equine patients with metabolic myopathies like acquired multiple acyl-CoA dehydrogenase deficiency.
• The outcome also backs treatment methods used for short-chain acyl-CoA dehydrogenase deficiency in humans with L-carnitine at the oral dosage of 100 mg/kg body weight per day.