Retinol uptake from retinol-binding protein (RBP) by liver parenchymal cells in vitro does not specifically depend on its binding to RBP.

The uptake characteristics of both the retinol and retinol-binding protein (RBP) moieties of the retinol-RBP complex by liver parenchymal cells (PC) in vitro were studied to assess whether retinol uptake is mediated by a cell-surface receptor for RBP. At 37 degrees C as well as 4 degrees C, [3H]retinol uptake from [3H]retinol-RBP showed a time-dependent increase, and was not saturable at concentrations exceeding the physiological concentration by more than a factor of 2 (3 microM). Uptake of [3H]retinol was not inhibited by a 10-fold molar excess of unlabeled retinol-RBP.

Role of lipoprotein lipase in the regulation of high density lipoprotein apolipoprotein metabolism. Studies in normal and lipoprotein lipase-inhibited monkeys.

Mechanisms that might be responsible for the low levels of high density lipoprotein (HDL) associated with hypertriglyceridemia were studied in an animal model. Specific monoclonal antibodies were infused into female cynomolgus monkeys to inhibit lipoprotein lipase (LPL), the rate-limiting enzyme for triglyceride catabolism. LPL inhibition produced marked and sustained hypertriglyceridemia, with plasma triglyceride levels of 633-1240 mg/dl.