A method for quantifying lipoprotein flux rates between plasma and arterial intima in vivo.

A new method is proposed for measuring in vivo the rates of transfer of plasma lipoprotein into and out of arterial intima in man. The technique requires the injection of a lipoprotein which can be labelled with two different tracers, followed by a single arterial sample during elective surgery. The feasibility of the method was tested by computer simulation and it was found that measurement uncertainties of the order of those likely in practice produced uncertainties of 7% SD in the calculated influx and 16% SD in the calculated efflux rates. The principal assumption, that lipoprotein in arterial intima can be modelled as a single compartment system, was tested in a preliminary study in an anaesthetised dog: reasonable evidence of monocompartmental behaviour was obtained. The new method was used in a preliminary study of three patients undergoing elective arterial surgery. Low density lipoprotein (LDL) labelled with 125I was injected about 24 h before surgery, followed by 131I-labelled LDL 4 to 6 h before surgery. The radioactivities of washed extracts of arterial intima were then measured in a gamma counter. LDL flux rates were higher in atherosclerotic specimens than in less seriously diseased or normal tissue, and were highest in the most hyperlipidaemic patient.