Splanchnic Metabolism of Plasma Apolipoprotein B: <i>STUDIES OF ARTERY-HEPATIC VEIN DIFFERENCES OF MASS AND RADIOLABEL IN FASTED HUMAN SUBJECTS</i>

P. R. Turner; N. E. Miller; C. Cortese; W. Hazzard; J. Coltart; B. Lewis

doi:10.1172/JCI110205

Splanchnic Metabolism of Plasma Apolipoprotein B: STUDIES OF ARTERY-HEPATIC VEIN DIFFERENCES OF MASS AND RADIOLABEL IN FASTED HUMAN SUBJECTS

P. R. Turner, N. E. Miller, C. Cortese, W. Hazzard, J. Coltart, and B. Lewis

Published June 1, 1981 - More info

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Abstract

The metabolism of apoprotein B-containing plasma lipoproteins by human splanchnic tissues has been studied in 29 men undergoing coronary angiography. Before catheterization autologous radio-iodinated lipoproteins were infused into a peripheral vein: 10 subjects received ¹²⁵I-labeled Sf 12-60 lipoproteins; 12 received ¹²⁵I-labeled Sf 12-60 plus ¹³¹I-labeled Sf 100-400 lipoproteins; and 7 received ¹²⁵I-labeled Sf 12-60 plus ¹³¹I-labeled Sf 0-12 lipoproteins. Paired arterial and hepatic vein blood samples were subsequently collected for replicate measurements of apoprotein B (apo B) mass, radioactivity and specific activity in each lipoprotein class. Splanchnic plasma flow was measured with indocyanine green. All studies were conducted after a 14-h overnight fast.

Newly synthesized apo B was shown to be secreted by splanchnic tissues as a component of Sf 100-400 lipoproteins, with no detectable uptake of apo B from this class. Sf 12-60 apo B was extracted by the splanchnic bed, with no detectable secretion. After continuous intravenous infusion of ¹²⁵I-labeled Sf 12-60 for five or more hours, 41-67% (mean 55%) of extracted Sf 12-60 apo B radioactivity reappeared in hepatic vein Sf 0-12 apo B. There was no detectable splanchnic catabolism of Sf 0-12 apo B.

The rates of Sf 100-400 apo B secretion, calculated as the product of artery-hepatic vein concentration difference and splanchnic plasma flow, were greater than the previously reported rates of very low density lipoprotein apo B turnover in fed subjects obtained by kinetic analysis of plasma specific radioactivity decay curves, suggesting that there may be a diurnal variation in hepatic apo B synthesis. They also exceeded the splanchnic extraction rates of Sf 12-60 apo B, suggesting there was some extrasplanchnic catabolism of the apo B of Sf > 60 lipoproteins.