Figure 5.

Inhibition of testosterone 6β-hydroxylase activity in microsomes prepared from 10 different human livers after preincubation with (a) verapamil and (b) diltiazem. Microsomes were preincubated with an NADPH generating system in the absence (control) or presence of 1 µm verapamil or 1 µm diltiazem for 30 min, followed by assay of testosterone 6β-hydroxylase activity. Mean (± s.d., n = 10 livers) testosterone 6β-hydroxylase activities for the control and inhibitor groups are also shown (○).