They are produced in the liver from free fatty acids. After hydrolysis, a VLDL cholesterol-rich remnant remains. This can be taken up by remnant receptors in the liver or converted to LDL by hepatic lipase. LDL are responsible for delivering cholesterol to peripheral tissues, including the adrenal glands, ovary and testes, through LDL receptors. They are produced in the gastrointestinal system and the liver.
Lipoprotein lipase is found in vascular endothelium.
It is activated by insulin, ACTH, TSH, glucagon and thyroid hormone. Its activity is enhanced by heparin. As discussed above, lipoprotein lipase hydrolyzes CM and VLDL to free fatty acids and glycerol and VLDL-remnants, respectively. The enzyme is stimulated by catecholamines, growth hormone, thyroxine, corticosteroids and prostaglandins. It is inhibited by insulin.