Re-examination on the sex-influenced esterase (ESSI) in rat serum.

The sex-limitation of sex-influenced esterase (ESSI) in serum of rats carrying Es-Sia allele was re-examined. ESSI was detected in immature males and females, and orchiectomized rats as well as mature females whereas ESSI in normal males rapidly disappeared with puberty. The rats orchiectomized at weaning temporarily lost ESSI around the age of sexual maturation, thereafter, ESSI reappeared. When orchiectomized rats were administered testosterone, synthesis of ESSI was suppressed as in normal adult males. Effect of ovariectomy was not recognized. The exceptional strain named SI 3 of which normal mature males have a significant level of ESSI has been established, although the level in the males is lower than that in the females of the same strain.