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Hyperglycemia Downregulates
Total Lipoprotein Lipase Activity in Humans
J. KOVÁŘ1,2, V. FEJFAROVÁ1,
T. PELIKÁNOVÁ1, R. POLEDNE1,2
1Institute for Clinical and Experimental Medicine,
and 2Centre for Experimental Cardiovascular Research,
Prague, Czech Republic
Received January 10, 2003
Accepted January 27, 2003
Summary
To address the question whether an increase in insulinemia and/or glycemia
affects the total activity of lipoprotein lipase (LPL) in circulation, the
enzyme activity was measured after periods of hyperinsulinemia (HI),
hyperglycemia (HG), and combined hyperinsulinemia and hyperglycemia (HIHG)
induced by euglycemic hyperglycemic clamp, hyperglycemic clamp with the infusion
of somatostatin to inhibit endogenous insulin secretion, and hyperglycemic
clamp, respectively. The results obtained were compared to those after saline
infusion (C). Twelve healthy normolipidemic and non-obese men with normal
glucose tolerance were included in the study. At the end of each clamp study,
LPL activity was determined first in vivo using an intravenous fat tolerance
test and then in vitro in postheparin plasma. Whereas isolated HI had no effect
on LPL activity in postheparin plasma, both HG and HIHG reduced LPL activity to
60 % and 56 % of that observed after saline infusion. Similarly, the k2
rate constant determined in intravenous fat tolerance test was reduced to 95 %,
84 %, and 54 % after periods of HI, HG, and HIHG, respectively. The activity of
hepatic lipase, another lipase involved in lipoprotein metabolism, was not
affected by hyperinsulinemia and/or hyperglycemia. In conclusion, our data
suggest that hyperglycemia per se can downregulate the total LPL activity in
circulation.
Key words
Lipoprotein lipase • Hepatic lipase • Glucose • Insulin •
Triglyceride
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