Regional expression and androgen regulation of carbonic anhydrase IV and II in the adult rat epididymis

Carbonic anhydrase (CA) is implicated in the acidification of epididymal fluid and thereby in the regulation of sperm maturation and motility. Among the CA isoenzymes, CA IV and II have been shown to be present in the rat epididymal duct epithelium. In the present study, we examined the expression and androgen regulation of CA IV and II mRNAs along the epididymal duct. Northern blot analysis revealed the presence of CA II mRNA in all regions of the epididymis with the strongest signal in the corpus region, while CA IV mRNA was expressed predominantly in the corpus epididymidis. Three days after bilateral castration, CA IV and II mRNAs were decreased by 80-90% in the corpus epididymidis. Testosterone (T) replacement maintained the expression of CA mRNAs at 50-60% of the control levels, indicating that circulating androgens alone are not sufficient to recover the CA expression in the corpus region. However, unilateral castration did not affect the mRNA levels of CA IV and II, suggesting that factors in testicular fluid do not play a major role in the regulation of CA expression in the corpus epididymidis. Immunoblot analysis showed that CA IV protein levels decreased 3 days after castration, while T administration maintained the protein expression virtually at the precastration levels. These data demonstrate that mRNAs for CA IV and II are predominantly expressed in the corpus region of the rat epididymis and can be regulated by androgens in that region. The present data suggest that the regulation of CA expression in the corpus epididymidis by androgens contributes to the known androgen effects on epididymal acidification.