Of the three ubiquitously expressed transforming growth factor-beta (TGF beta) receptors, only type I and type II receptors contain serine/threonine kinase activity and have a direct role in TGF beta signal transduction. In the prostate, it has been reported that the level of type III receptor expression increases transiently after castration. However, the relationship between the TGF beta signaling receptors, type I and type II, and androgen is currently unclear. Thus, in the present study, we made an initial attempt to elucidate the effect of androgen on type I and type II receptor expression in the rat ventral prostate by measuring the levels of messenger RNA (mRNA) and protein at specific time points after castration up to 10 days. Within 3 days after castration, an increase in type II receptor mRNA was observed in the prostate, and the level continued to rise until 7 days postcastration (approximately 8-fold increase). Between days 7-10 postcastration, no significant change in the level of type II receptor mRNA was observed. Testosterone administration immediately after castration abolished the induction of type II receptor mRNA during the same 10-day period. Western blot analysis performed for type II receptor showed a similar result, in that the level of type II receptor protein increased approximately 5-fold by day 10 postcastration. In a similar manner to the expression of type II receptor mRNA, the level of type I receptor mRNA increased steadily until day 7 postcastration (approximately 6-fold increase). Between days 7-10 postcastration, the level of type I receptor mRNA did not change significantly. As with type II receptor mRNA, the induction of type I receptor mRNA was suppressed when testosterone was administered immediately after castration. To localize the expression of TGF beta receptor type II, immunohistochemical studies were performed. The results of these studies demonstrated a preferential localization of type II receptor in the prostatic epithelial cells and an increased staining intensity for the receptor after castration. Taken together, these data indicate that TGF beta signaling receptors, type I and type II, are under negative androgenic regulation at the transcriptional level and that TGF beta may be an important regulator of a stromal-epithelial interaction in the rat ventral prostate.