[Lipoproteins as a factor regulating vascular tonus]

Lipoproteins (very low, low and high density) purified from canine fresh plasma produced relaxation of isolated dog coronary artery and rabbit aortic ring segments precontracted with potassium, 30 mM or phenylephrine, 10(-6) M, respectively. No apparent species-specific effects of lipoproteins were revealed and they produced relaxation of other species vessels as well, which differed quantitatively. No apparent endothelium-dependent relaxation produced by animals' lipoproteins was evident. The interference of lipoproteins with some steps in electromechanical coupling is suggested which seemingly result to decrease in excitability of voltage and receptor operated calcium channels of smooth muscle cell membrane. The role of lipoproteins seems to be in maintenance of low level of smooth muscle cell membrane excitability.