MASCULINIZATION AND DEFEMINIZATION OF FEMALE RATS BY MALES LOCATED CAUDALLY IN THE UTERUS

It is assumed that female rats are masculinized by the presence of males in the same uterine horn. Two hypotheses regarding the mechanism have been proposed: 1) interamniotic diffusion of androgens (contiguity hypothesis) and 2) transport of androgens via the bloodflow (caudal male hypothesis). This study was designed to test these hypotheses while taking into account two previously uncontrolled factors: hemihysterectomy of the mother during pregnancy and birth by caesarean section. Pregnant females were hemihysterectomized during pregnancy or left intact; pups were born naturally or through caesarean section. Position in utero was determined. In adulthood all females were ovariectomized and tested for mounting behavior before and during testosterone treatment and lordosis behavior during estradiol treatment. It was found that females with males located caudally in the same uterine horn were more masculinized and defeminized than females without such males. Adjacent males had no influence on the behavioral sexual differentiation of females. These results confirm the "caudal male hypothesis" rather than the "contiguity hypothesis." Hemihysterectomy during pregnancy prevented the "caudal male effect." Birth through caesarean section did not interfere with the caudal male effect. © 1990.