Plasma turnover of Sf 0–9 low-density lipoprotein in normal men and women

Abstract

Experiments were performed to investigate the lower plasma low-density lipoprotein concentrations seen in premenopausal female populations compared with men or older women. Turnover studies were performed on normal subjects, using their own low-density lipoprotein radioiodinated in the peptide component.Most studies could not be prolonged past 17 days, but it appeared that equilibration of plasma and extravascular compartments was generally incomplete at this stage. In two studies maintained for 6 weeks, equilibration appeared to require more than 3 weeks; turnover rates were slower than has previously been suspected, and the extravascular pool contained about half the total body radioactivity.The 17-day studies appeared to provide quantitatively accurate parameters of lipoprotein fractional catabolic rates (obtained from urinary measurements) but not of plasma half-lives. Ten young women as a group showed significantly faster fractional turnover rates than did 10 men or 3 older women.In men and young women, serum low-density lipoprotein levels had no correlation with fractional catabolic rates, but did correlate with absolute catabolic rates, suggesting that a fixed proportion of the plasma pool may be catabolised daily (although at different rates between the sexes). Results from the 3 older women suggested that a simple relationship between serum low-density lipoprotein levels and absolute catabolic rate may not apply to all age groups. Possible mechanisms of lipoprotein metabolism are discussed in the light of these results.