Ah receptor and ARNT protein and mRNA concentrations in rat prostate: effects of stage of development and 2,3,7, 8-tetrachlorodibenzo-p-dioxin treatment.

Effects of stage of development and 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) exposure on aryl hydrocarbon receptor (AhR) and AhR nuclear translocator (ARNT) protein concentrations in reproductive organs of male rats were determined. AhR protein levels in developing rat ventral and dorsolateral prostate decreased with age, declining approximately 70% between Postnatal Days (PND) 1 and 21. ARNT protein levels also decreased with age in dorsolateral, but not ventral prostate. The developmental decreases in prostatic AhR and ARNT protein were associated with decreases in AhR and ARNT mRNA. AhR and ARNT protein concentrations in fetal urogenital sinus on Gestation Days (GD) 16, 18, and 20 were similar to levels in ventral prostate on PND 7. TCDD exposure of adult male rats (0.2, 1, 5, or 25 micrograms/kg po, 24 h) decreased AhR but not ARNT protein in ventral and dorsolateral prostate, vas deferens, and epididymis. In utero and lactational TCDD exposure (1.0 micrograms/kg dam po, GD 15) did not alter ARNT levels but reduced prostatic AhR protein levels on PND 7 and delayed the developmental decrease in AhR protein in ventral and dorsolateral prostate. Finally, pretreatment of rat pups for 24 h with TCDD (5 micrograms/kg ip) down-regulated prostatic AhR protein on PND 7, but not on PND 1. Thus, prostatic AhR and ARNT protein and mRNA levels are regulated with age, whereas only AhR protein concentration is altered by TCDD exposure. Because in utero and lactational TCDD exposure only decreased prostatic AhR on PND 7, it is unlikely that down-regulation of AhR is the mechanism by which perinatal TCDD exposure impairs prostate development.