Lipoproteins as factors in vessel tone and reactivity modulation

Lipoprotein fractions purified from fresh canine plasma--very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL)--produce relaxation of isolated ring segments of coronary arteries of canine (porcine and human) and rabbit aorta precontracted with high potassium, 30 mM, or phenylephrine, 10(-6) M, respectively. Lipoproteins do not possess high species specificity and produce relaxation of arteries of other species which differ quantitatively. There was no marked endothelium-dependent relaxation induced by animal lipoproteins although human LDL produced endothelium-dependent relaxation induced by animal lipoproteins although human LDL produced endothelium-dependent relaxation of rabbit aortic rings. Canine LDL and HDL decreased endothelium-dependent relaxation of rabbit aortic rings produced by acetylcholine (10(-9)-10(-6) M), which was more pronounced when the LDL and HDL were present in the organ bath. In this case, LDL and HDL reduced the rate of development and amplitude of contraction produced by phenylephrine, 10(-6) M. We suggest that lipoprotein effects may result from blockade of some steps in electromechanical coupling or from inhibition of voltage- and receptor-operated Ca-channels of vessel smooth muscle cell membrane.