Studies on equine lipid metabolism. 2. Lipolytic activities of plasma and tissue lipases in large horses and ponies.

The research investigates the lipolytic activities in large horses and ponies, focusing on key enzymes affecting lipid metabolism. Findings suggest the differences in regulation of triglycerides release from fat stores could cause hyperlipaemia in ponies.

Objective of the Research

• The researchers aims to explore the enzymatic fundamentals of lipid metabolism in equine, specifically difference between large horses and ponies. It quantitatively analyzed the activity rate of important enzymes that break down triglycerides in these two subspecies.
• The study also aimed to gain insights into the causes of hyperlipaemia (excessive fat in the blood) in ponies during negative energy balance (when energy used exceeds energy consumed).

Methodology

• Researchers measured the activities of three enzymes: hormone-sensitive lipase (HSL), lipoprotein lipase (LPL), and hepatic triglyceride lipase (HTGL) in ex vivo (in an artificial environment outside the organism) in vitro (in the glass/ test tube) conditions.
• Norepinephrine (NE), a hormone that triggers fat cells to release free fatty acids (FFA), was applied to pony adipocytes (fat cells) to track the release of FFA.
• The lipolysis (fat breakdown) rate, both in a normal state and when adenosine deaminase (ADA; an enzyme that converts adenosine to inosine) and NE were added, was compared between ponies and horses.
• The researchers also studied the impact of insulin on lipolysis and compared the FFA release level from pony fat cells to the maximum NE and ADA-stimulated lipolysis in horse adipocytes.
• Lipase activities in postheparin plasma, as well as the LPL activity in adipose and muscle tissues, were compared between horses and ponies to validate the findings.

Findings and Conclusion

• The researchers found that NE stimulated the release of FFA from pony adipocytes but not in horses.
• When ADA and NE were added, lipolysis was significantly higher in pony fat cells compared to horse adipocytes.
• Despite the similar relative inhibition of lipolysis by insulin in both species, the absolute FFA release was higher in pony fat cells.
• The lipase activities in postheparin plasma did not significantly differ between ponies and horses. This was also true for LPL activity in adipose and muscle tissues.
• The study concluded that the development of hyperlipaemia in ponies might be attributed to the differences in regulation of triglyceride release from fat cells rather than the clearance of triglycerides from the bloodstream.