cDNA clones for rat muscle carbonic anhydrase III have been isolated from a λ gt-11 library and sequenced. Comparison with human CAIII cDNA showed about 90% homology to rat. The rat clones were used to estimate mRNA from liver and muscle on Northern blots and showed that the sexual dimorphism of CAIII in rat liver relates to a difference in mRNA levels.
Carbonic anhydrase (CA) isozymes CAII and CAIII are known to exhibit sexual dimorphism in rat liver, and the levels of these isozymes are affected by sex hormones. In this paper we show that the isozyme CAI is present at low levels in rat liver, with no difference in concentration between male and female rats. Estrogen and diethylstilbestrol reduce CAI levels in both sexes.
The concentration of carbonic anhydrase IlI (CAIII) in male rat liver was found to be 30 times greater than that in the female. Castration of male rats led to marked reduction in liver CAIII concentrations which could be partially restored to control levels by testosterone replacement. Marked developmental and senescence changes in liver CAIII were also observed in male rats.