A sex-limited serum protein of Syrian hamsters: definition of female protein and regulation by testosterone.

Normal Syrian hamster females contain a serum protein not found by simple gel diffusion assay in normal adult males. This sex-limited protein was called female protein (FP). Low levels of FP were found in sera from normal weanling male hamsters. Adult male hamsters castrated or treated with diethylstilbestrol also developed serum FP, which could be suppressed by administration of testosterone. Exogenous testosterone also suppressed serum FP in adult females, and ovarian function did not appear to be critical for maintenance of serum FP. Although FP is present in significant amounts (1-2 mg/ml) in adult females, its function is presently unknown.