Dimethoate blocks pubertal differentiation of Leydig cells in rats.

Dimethoate is an organophosphate pesticide. It is widely used in agriculture. However, whether it blocks pubertal development of Leydig cells remains unknown. In the current study, we exposed male Sprague Dawley rats with 7.5 and 15 mg kg dimethoate from postnatal day 35-56. We also exposed Leydig cells isolated from 35-day-old rats for 3 h. Dimethoate reduced serum testosterone levels at 7.5 and 15 mg kg-1 but increased serum luteinizing hormone and follicle stimulating hormone levels at 15 mg kg-1. Dimethoate did not influence Leydig cell number but reduced Leydig cell size and down-regulated Star, Cyp11a1, and Hsd3b1 in Leydig cells as well as their protein expression. Dimethoate inhibited basal androgen output in a dose-dependent manner with the inhibition starting at 0.05 μM. It significantly inhibited luteinizing hormone and 8Br-cAMP stimulated androgen outputs at 50 μM. It significantly inhibited 22R-hydroxycholesterol and progesterone-mediated androgen outputs at 50 μM. Further study demonstrated that dimethoate also down-regulated the expression of Star, Cyp11a1, and Hsd3b1 at 5 or 50 μM in vitro. Dimethoate did not directly inhibit rat testicular steroidogenic enzyme activities at 50 μM. In conclusion, dimethoate targets Star, Cyp11a1, and Hsd3b1 transcription, thus blocking Leydig cell differentiation during puberty.