Studies on the source of urinary cholesterol in the normal human male.

The aim of the present study was to obtain information on the source of urinary cholesterol in normal men of various age groups (22-25, 37-42, greater than 63 yrs). Aliquots of 24-hr urine samples were fractionated by ultracentrifugation. Between 10-20% of the total cholesterol in urine (measured by gas-liquid chromatography) separately sedimented after 2 x 10(4) g-min and after 4 x 10(5) g-min of centrifugation. However, an average of more than 50% of the total sedimented after 6 x 10(6) g-min and only 10-20% of total cholesterol remained in this supernatant. These results indicate that most of the cholesterol in urine of normal males is a component of a light particulate fraction. Little difference was seen in the distribution of urinary cholesterol among the various age groups examined The 4 x 10(5) g-min supernatant from 24-hour total urine samples was recentrifuged at 10(5) g for 60 min. The resulting pellet (100 P) was assayed for protein, total cholesterol and phospholipid. The cholesterol was 12-14% esterified. A molar ratio of total cholesterol to phospholipid of 1 to 0.8 was calculated. Assay of the 100 P fraction for marker enzymes showed an activity pattern characteristic for plasma membranes. Fractionation of the 100 P proteins by electrophoresis and separation of the 100 P phospholipids by thin-layer chromatography revealed patterns clearly different from those of human red cell plasma membrane. Electron micrographs of the 100 P fraction revealed an appearance similar to that of deteriorated membranes. The results suggest that most of the cholesterol in urine of the adult human male is present as a component of membranes derived from endogenous cells of the urogenital system.