Alpha 1-blockers (e. g., doxazosin, prazosin) are reported to have beneficial effects on plasma lipid and lipoprotein levels. We investigated the effect of naftopidil, a new alpha 1-blocker, on 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase and low density lipoprotein (LDL) receptor in cultured human skin fibroblasts in comparison with doxazosin. Naftopidil inhibited HMG CoA reductase activity and increased LDL receptor activity in a dosed-dependent manner. Doxazosin also inhibited HMG CoA reductase activity and increased LDL receptor activity. The changes in HMG CoA reductase and LDL receptor activity with naftopidil equal of approximately 10% of those changes obtained with doxazosin. Considering that the alpha 1-blocking property of naftopidil equals one-tenth of the blocking property of doxazosin, alpha 1-blockers seem to act on HMG CoA reductase and LDL receptor through the alpha 1-receptor.
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