Inhibition of the in vitro renin reaction by circulating neutral lipids

We have previously reported that the addition of plasma from normotensive human subjects to renin-renin substrate inhibits the in vitro rate of angiotensin generation. The purpose of the present study was to determine whether a renin-inhibiting factor could be identified in human plasma. Neutral lipids and phospholipids were extracted from plasma of seven normotensive control subjects. During 30-, 60-, and 180-minute incubations, neutral lipids inhibited the reaction between human renin and homologous renin substrate (P less than 0.01). Phospholipids did not affect the rate of angiotensin generation (P less than 0.05). The neutral lipid extract was further separated on silica gel chromatographic plates, and several fractions inhibited renin (P less than 0.01) Addition of each of six synthetic neutral lipids to renin-renin substrate did not affect the rate of angiotensin generation. In conclusion, several neutral lipid fractions extracted from human plasma inhibit the in vitro renin reaction.