4.1.4. Triglycerides

Triglycerides are another group of lipids involved in lipid metabolism that accounts for the majority of the lipids found in adipose tissue. They are synthesised primarily in adipose tissue, the liver, small intestine, and mammary glands. Circulating concentrations of triglycerides in normal animals reflect the balance in triglyceride absorption by the small intestine, synthesis/secretion by the hepatocytes and uptake by the adipose tissue. This balance is affected by the concentration of fat in the diet and by the production of hormones such as insulin and glucagon [47]. The triglyceride levels were significantly elevated in cold-blooded stallions to such an extent that the levels in cold-blooded and warm-blooded stallions were equal (Figure 6), which indicates that knotweed stimulated lipid metabolism in cold-blooded stallions but not in warm-blooded horses whose metabolic activities were already high.

Many studies ascribed the lowered concentration of triglycerides in the blood of different species to different active compounds from knotweed [48–52]. This study found the opposite: an increase of triglyceride concentration in the blood of knotweed-fed coldblooded horses. The mechanism behind the increased triglycerides is not clear. This increase could be due to the different physiologies of horses or to specific active compounds from knotweed, or a combination of both. The anatomy and physiology of digestion is partly different in horses than in all of the others species, including humans, that have been tested in previous studies. A horse has no gallbladder. It means that bile is constantly passing from the liver directly to the intestine through bile duct. Pancreatic juice also constantly flows directly into the intestine. The production or release of gall and pancreatic juice in horses is not dependent on the food in the intestine or on the amount of lipids in feed like in other mammals [53]. If some active compounds from knotweed, such as piceatannol, could change the amount of bile acids in the gall, different amounts of lipids from food could be absorbed. Epicatechin-3-O-gallate from knotweed could increase the concentration of triglycerides in the blood by blocking lipase [48,54]. The horses in this study were fed a common diet without higher amounts of lipids and statistically significant results were within physiological ranges. We cannot say whether the triglyceride levels were increased due to the absorption from food or the release from adipose tissues. Answers to these questions are beyond the scope of this study. However, it shows an interesting potential of knotweed supplementation to support the breeding and performance of coldblooded horses.
