Fetal Growth Restriction Leads to Inhibition of Steroidogenesis.

Abstract

Masculinization of the male reproductive tract occurs in humans from gestational weeks 10-22, and from gestational days 16-21 in rats. During this programming window, fetal testes produce a surge of testosterone causing reproductive masculinization. Disruption of this fetal testosterone production has been shown to result in various reproductive abnormalities including cryptorchidism and hypospadias. It is unknown what specifically causes these reproductive abnormalities aside from genetic defects of the steroidogenic pathway. In humans, in utero growth restriction is a well-known risk factor for cryptorchidism and hypospadias, but the mechanism is unknown. In addition, previous rat studies have suggested that fetal testosterone production can be disrupted by several factors including environmental exposure to anti-androgens such as dibutyl phthalate (DBP). In order to identify the mechanism underlying male reproductive malformation associated with in utero growth restriction, a maternal under-nutrition model was examined in the rat. Timed-pregnant Wistar rats were restricted to 50% (n=9) of the food eaten by ad libitum control dams (n=8) beginning on gestational day (GD) 3. Caloric restriction through GD17 resulted in a significant decrease in pup weight despite no significant decrease in litter size. Cultured fetal testes revealed a decrease in testosterone production of about 40% as indicated by radioimmunoassay. Additionally, mRNA levels of key components in the steroidogenic pathway including Scarb1 and Star were significantly decreased in the testis following in utero growth restriction. Analysis of postnatal endpoints following 50% caloric restriction (n=11) from GD3-18 indicated no evidence of undescended testes, hypospadias, and no significant decrease in anogenital distance at postnatal days 1, 14, or 28 as compared to ad libitum control animals (n=10). A coexposure study of in utero growth restriction and maternal dosing with the anti-androgen dibutyl phthalate was performed to determine if there was a cooperative effect on steroidogenesis. Analysis of fetal testes (GD17) following 50% maternal caloric restriction from GD3-17 (n=11) or exposure to DBP (250mg/kg bw/day) from GD15-17 without food restriction (n=7) showed a significant decrease in the expression of the steroidogenic genes Cyp11a1, Cyp17a1, Scarb1, and Star as compared to ad libitum controls (n=7). Moreover, when 50% caloric restriction was coupled with exposure to DBP (n=10), steroidogenic gene expression was further decreased. These results indicate that not only do in utero growth restriction and fetal exposure to DBP lead to a decrease in testosterone production separately, they also appear to work cooperatively to further disrupt the steroidogenic pathway. This interaction between chemical endocrine disruptor exposure and in utero growth restriction could begin to explain the mechanisms associated with human male reproductive abnormalities.