Figure 5. Testosterone production by isolated Leydig cells in vitro. Cells from 4-20-month-old rats were incubated with luteinizing hormone (100 ng/ml), dibutyryl cyclic adenosine monophosphate (1 mM), 2R-hydroxycholesterol (20 µM), or pregnenolone (2.5 µM). The bars are the mean ± standard error of the mean, generated as described for Figure 1. ^*Significant difference from the 4-month-old value.