The purpose of this study was to examine whether an absence of
triglyceride-rich
lipoproteins (
chylomicrons and
very-low-density lipoproteins) in plasma is associated with any changes in the
enzyme activity of
lipoprotein lipase or hepatic
lipase after
heparin administration. To study this, the activities of hepatic
lipase and
lipoprotein lipase were determined in control subjects, in two patients with heterozygous
hypobetalipoproteinemia, and in three patients with phenotypic
abetalipoproteinemia after administration of
heparin. Both
enzymes showed normal activity in the patients with
hypobetalipoproteinemia, but showed consistently reduced activity in the patients with
abetalipoproteinemia. Hepatic
lipase activity in plasma samples from these three patients obtained 15 minutes after
intravenous injection of
heparin was 55%, 87%, and 46% of that of the controls, whereas corresponding values in plasma samples obtained 30 minutes after
heparin were 47%, 70%, and 57%, respectively.
Lipoprotein lipase activity in the three patients with
abetalipoproteinemia was 46%, 29%, and 34% of that of the controls in the samples obtained 15 minutes after
heparin injection, whereas the values obtained after 30 minutes were 53%, 64%, and 47% of that of the controls. We conclude that an inherent absence of
triglyceride-rich
lipoproteins, as occurs in
abetalipoproteinemia, is associated with reduced
enzyme activity of both hepatic
lipase and
lipoprotein lipase in plasma after
heparin administration.