Mechanism for the Generation of Active Smooth Muscle Inhibitory Factor (IF) from Bovine Retractor Penis Muscle (BRP)

The active smooth muscle inhibitory factor (IF) is generated by acidifying the extracts from the bovine retractor penis muscle (BRP). The activated IF is very similar to endothelium-derived relaxing factor (EDRF). However, the mechanism for the generation of active IF is yet unknown. From reverse-phase high performance liquid chromatographic data, the activities of nitrite loss were closely related to the contents of both sulfhydryl (SH) groups and L-cysteine. Thus, under acidic conditions, RSH and nitrite in the extracts are considered to react as follows: RSH + HNO2----RSNO + H2O, RSNO----(1/2) RSSR + NO, NO + (1/2)O2----NO2, NO2 + (1/2)H2O----(1/2)HNO2 + (1/2)HNO3. In addition to NO, RSNO is also a labile but potent vasodilator. Thus, activated IF seems to consist of RSNO and NO, and thiol-containing small molecules (molecular weight of less than 1,000) from BRP are closely involved in the generation of active IF.