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 (TC DD) exposure on aryl hydrocarbon receptor (AhR) and AhR nuclear translocato r (ARNT) protein concentrations in reproductive organs of male rats were de termined. AhR protein levels in developing rat ventral and dorsolateral pro state decreased with age, declining approximately 70% between Postnatal Day s (PND) 1 and 21. ARNT protein levels also decreased with age in dorsolater al, but not ventral prostate. The developmental decreases in prostatic AhR and ARNT protein were associated with decreases in AhR and ARNT mRNA. AhR a nd 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. TC DD exposure of adult male rats (0.2, 1, 5, or 25 mu g/kg po, 24 h) decrease d AhR but not ARNT protein in ventral and dorsolateral prostate, vas defere ns, and epididymis. In utero and lactational TCDD exposure (1.0 mu g/kg dam po, GD 15) did not alter ARNT levels but reduced prostatic AhR protein lev els on PND 7 and delayed the developmental decrease in AhR protein in ventr al and dorsolateral prostate. Finally, pretreatment of rat pups for 24 h wi th TCDD (5 mu g/kg ip) down-regulated prostatic AhR protein on PND 7, but n ot on PND 1. Thus, prostatic AhR and ARNT protein and mRNA levels are regul ated with age, whereas only AhR protein concentration is altered by TCDD ex posure. Because in utero and lactational TCDD exposure only decreased prost atic AhR on PND 7, it is unlikely that downregulation of AhR is the mechani sm by which perinatal TCDD exposure impairs prostate development. (C) 1999 Academic Press.