Effect of propranolol on lecithin:cholesterol acyl transferase activity in vitro

Recently propranolol was found to inhibit human lecithin: cholesterol acyl transferase (LCAT) activity both after oral treatment and after addition to plasma in vitro. Now the dose-response relationship of the propranolol effect on LCAT activity was evaluated in vitro. Concentrations required to produce half-maximal effects in 7 men ranged from 32.4 to 121.4 nmol/l which corresponds to the therapeutical concentration range of the drug. Complete inhibition could not be achieved. The maximal effect (propranolol-sensitive LCAT activity) varied between subjects depending on the preexiting lecithin: cholesterol acyl transfer rate in plasma. Propranolol mediated inhibition of LCAT activity could be abolished when heat-inactivated plasma instead of native plasma was used as LCAT substrate. It is concluded that the interindividual variability of propranolol-sensitive LCAT activity may reflect differences in the thermoinstable lipoprotein structure.