OR CASTRATED HAMSTERS

Experiments were designed to discover if oestradiol benzoate induces loss of fertilizing ability of hamster epididymal spermatozoa by acting directly on the cauda epididymidis. Spermatozoa were retained in the cauda epididymidis by ligating the distal corpus epididymidis and proximal ductus deferens and fertilizing ability was compared in oestrogen-treated, intact hamsters and in castrated or hypophysectomized animals maintained with testosterone. Fertility tests showed that 12 daily s.c. injections of 3\m=.\5or 5 \g=m\goestradiol benzoate reduced fertilizing ability to 35\m=.\2and 0 %, respec-tively; supplementary testosterone did not prevent the adverse effect of oestrogen and reduced fertilizing ability was shown not to be related to a deficiency of circulating testosterone as judged by fructose concentration in the seminal vesicles. Daily treatment of androgen-maintained castrated or hypophysectomized hamsters with 3\m=.\5\g=m\goestradiol benzoate for 12 days reduced fertilizing ability to 43\m=.\7and 31\m=.\3%,respectively. The results suggest that oestradiol benzoate reduces fertilizing ability in hamsters by acting directly on the cauda epididymidis and inhibiting the effect of testosterone