Sex-Related Differences in Blood and Gonad Levels
of Testosterone in Silver Fox Fetuses

L. V. Osadchuk

Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences,
ul. Akademika Lavrent’eva 10, Novosibirsk, 630090 Russia

Received December 8, 1999; in final form, March 23, 2000

Abstract—The mass of silver fox fetuses of both sexes, their gonads, and adrenals, and the levels of testoster-
one in the blood serum and in gonads and adrenals were determined from day 31 of gestation and every five
days thereafter until its termination. Marked sex-related differences were revealed: the blood and gonad levels
of testosterone in male fetuses were much higher than those in female fetuses. The fetal adrenals contained sig-
nificantly less testosterone than the gonads. No sex-related differences in the content of testosterone in the fetal
adrenals were found. No differences were found in the body and adrenal mass in female and male fetuses at all
the developmental stages studied, while the mass of ovaries exceeded that of testes from day 45 of gestation.
The data obtained suggest sex dimorphism in the production of testosterone by gonads in silver foxes appears
after day 35 and appears to correspond to the period of morphological differentiation of gonads.

Key words: silver fox, testosterone, fetal gonads, fetal adrenals, prenatal development

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