Comparative evaluation of nonylphenol isomers on steroidogenesis of rat Leydig Cells

► Effects of p33-NP, p262-NP, p353-NP and p363-NP on steroidogenesis were tested. ► NP isomers showed varying degrees of inhibition of testosterone biosynthesis. ► p363-NP led to the most significant decrease in testosterone level. ► NP isomers down regulated Hsd3b, Cyp11a1 and Star expression to various extent. ► NP isomers induced enhancement of Leydig cell apoptosis in various degrees.