Composition and metabolism of very low density lipoproteins in dog cardiaclymph

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Abstract
Very low density lipoprotein (VLDL, d [density] < 1.006) in cardiac lymph was characterized to determine its role as a metabolic substrate in the interstitial compartment. A major efferent cardiac lymph trunk was cannulated in fasting (18 h) dogs (20-27 kg). Three to 5 ml of lymph were collected over 3-4 h at 4.degree. C. Cardiac lymph VLDL concentration was 1.7 .+-. 0.7 mg protein.cntdot.100 ml-1 vs. 1.8 .+-. 0.8 mg protein.cntdot.100 ml-1 in plasma. The VLDL triglyceride concentration in lymph was 1.0 .+-. 0.3 mg triglyceride.cntdot.100 ml-1 with triglyceride/protein ratio of 0.9 vs. plasma VLDL triglyceride of 5.0 .+-. 1.6 mg.cntdot.100 ml-1 with a triglyceride/protein ratio of 5.5. EM of VLDL revealed globular particles with a mean diameter of 388 .ANG. in lymph and 661 .ANG. in plasma. Cardiac lymph VLDL are smaller and contain less triglyceride per particle than plasma VLDL. Following i.v. administration of human 125I-labeled low density lipoprotein ([125I]LDL, d 1.025-1.045), cardiac lymph/plasma LDL specific activity ratio was 0.52 .+-. 0.15 (n = 3) and 0.55 .+-. 0.15 (n = 4) at 3 and 27 h, respectively. The fact that the specific activity ratio did not reach 1 at plateau suggests continuous addition of unlabeled LDL in the cardiac interstitium, presumably from VLDL precursors. On a protein basis the concentration of VLDL in cardiac lymph equals that of plasma. VLDL degradation and LDL production apparently occur in the cardiac interstitial space.