Trypsin inhibition by mouse serum: sexual dimorphism controlled by testosterone.

The trypsin inhibiting activity in the serum of male mice is substantially greater than that in females. In five strains of mice and two large groups of interstrain hybrids this difference ranged from 14 (in ICR mice) to 55 percent (in DBA mice). Castration of males significantly decreased the serum trypsin inhibiting activity, whereas the administration of testosterone restored the activity to its original level. Administration of testosterone to female mice increased the activity to a level similar to that in males of the same strain. Because almost all the change in inhibiting activity occurred in the electrophoretic alpha-1 region, alpha-1 region, alpha-1-antitrypsin is probably responsible for this effect.