Lipoprotein composition and transport in the pig and dog cardiac lymphatic system.

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Abstract
The cardiac lymphatic system of pigs consisted of valved efferent lymph vessels draining into a cardiac lymph node, which is similar to the lymphatic system found in dog and man. The interstitial lipoproteins of the heart were studied by sampling cardiac efferent lymph in anesthetized fasting pigs (n = 4) and dogs (n = 5). In pigs, the lymph flow rate was 2.0 .+-. 0.7 ml/h and in dogs, 1.2 .+-. 0.3 ml/h. The total cholesterol concentration was 54.9 .+-. 8.0 and 53.6 .+-. 6.3 mg/100 ml in cardiac lymph of pigs and dogs, respectively. The ratio of lymph:plasma cholesterol differed in the 2 species: 0.62 in pigs and 0.46 in dogs. More than 90% of cardiac lymph cholesterol was recovered in high density lipoprotein (HDL) and in low density lipoprotein (LDL) in pigs and dogs. In pigs, LDL was the major cholesterol-carrying lipoprotein in plasma and lymph; in canine plasma and lymph, this was HDL. The appearance of 125I-LDL in canine cardiac lymph following i.v. administration was rapid and reached a plateau by 1 h. The t1/2 [half-time] appearance of 125I-LDL in lymph was 5 min compared to t1/2 clearance of plasma (rapid phase) of 44 min. The lymph:plasma ratio of LDL specific activity was 0.48 .+-. 0.15, suggesting continuous addition of cold LDL in the interstitial space. The high concentration and turnover of cholesterol-rich lipoprotein in cardiac lymph suggest that the predilection of the coronary bed for atherosclerotic degeneration may be a function of the interstitial lipoprotein concentration and composition and the plasma concentration of lipoprotein species.