Long-Term Effects of Neonatal Administration of Estrogen and Progesterone, Alone or in Combination, on Male BALB/c and BALB/cfC3H Mice

Newborn BALB/c and BALB/cfC3H male mice were given five daily injections of 17β-estradiol and progesterone, alone and in combination, beginning within 36 hr after birth. Mice were killed and autopsied between 19 and 27 months of age. Mice treated neonatally with 17β-estradiol showed a complete inhibition of spermatogenesis in 71% of the BALB/c substrain (compared with 30% in the controls) and in 62% of the BALB/cfC3H substrain (compared with 0% in the controls), with 8 and 10 animals, respectively, having at least one testis completely atrophied. Estradiol alone resulted in epididymal cysts and some metaplastic changes in the secondary sex accessories in both substrains. Estradiol/ progesterone combinations resulted in similar abnormalities in the male genital tract of both substrains, whereas progesterone alone was not so effective.