Initial plasma high-density lipoprotein distribution in the rat: effects of age, sex, and fasting

The initial tissue distribution of high-density lipoprotein (HDL) was studied in the rat. Specific tissue-space measurements, calculated as the difference between HDL and albumin uptake in a tissue, 10 min after injecting radiolabeled lipoprotein, were taken to represent specific binding of HDL. Rat HDL (rHDL) and human HDL3 (hHDL3) were labeled directly with 125I or with prelabeled 125I-apolipoprotein A-I (125I-apoA-I). Specific tissue spaces were demonstrated for the liver and adrenals but not for spleen, jejunum, ileum, colon, muscle, or adipose tissue. The kidney showed a specific HDL space only when 125I-apoA-I-rHDL was injected. The adrenals bound rHDL to a greater extent than hHDL3, and the liver also bound from three to five times more rHDL than hHDL3. In male and female rats the liver accounted for about two-thirds of total HDL bound. Significantly more HDL was bound by adrenals of female than by male rats, but the reverse occurred for liver and kidney. The greater hepatic binding of HDL in males compared to females was consistent with measurements of HDL flux, calculated from constant infusions of labeled HDL; the fractional clearance of 125I-apoA-I-rHDL was 572 +/- 13 microliter plasma X h-1 X 100 g body wt-1 in males and 466 +/- 19 microliter plasma X h-1 X 100 g body wt-1 in females (P less than 0.01). Tissue-space measurements with 125I-rHDL were not affected by age. Fasting for 48 h increased HDL binding by liver but not by adrenals.(ABSTRACT TRUNCATED AT 250 WORDS)