Expression of the androgen receptor gene in rat penile tissue and cells during sexual maturation.

The cessation of rat and human penile growth at completion of sexual maturation appears to be related to a tissue-specific decrease in the number of androgen receptors (AR) in the penis. To find out whether this is due to either transcriptional or translational regulation of the AR gene, we determined the levels of AR mRNA by Northern blots in the corpora cavernosa from groups of 16-, 19-, 22-, 27-, 52-, and 90-day-old rats. The AR mRNA rapidly decreases with age and is nearly undetectable in the 52- and 90-day-old rats, paralleling the decline in AR number. The persistence of a low amount of AR mRNA in the adult penis was confirmed by reverse transcription/polymerase chain reaction amplification of total RNA, and its level was estimated by a semiquantitative modification of this procedure at less than 1/25th of that found in the youngest rats. Smooth muscle cells derived from the 16- and 90-day-old corpora cavernosa express in the AR gene in vitro in approximately the same levels, suggesting that there are factors in culture that up-regulate the AR mRNA. Our results are compatible with the assumption that the age-dependent decrease in AR in the rat penis is due to transcriptional regulation, although they do not exclude the less likely alternative of a selective effect on AR mRNA stability and support the use of this model for studying tissue-specific factors controlling the developmental expression of the AR gene.