Uterine position and the activation of male sexual activity in testosterone propionate-treated female guinea pigs.

Fetal female guinea pigs were delivered surgically and their position within a uterine horn relative to male fetuses was noted. When adult they were ovariectomized, injected daily with testosterone propionate, and examined for male copulatory behaviors in response to the presence of a receptive female. Females that developed contiguous to a caudal male were functionally similar to those that had been situated between two males; both exhibited enhanced levels of mounting relative to females that were located contiguous to no males (with and without the presence of a caudal male) and to females contiguous to a cephalic male. Therefore, both contiguity and positioning of the male fetus are necessary conditions for prenatal masculinization of the female guinea pig. Lastly, four animals that had resided singly in the uterus displayed the lowest levels of copulatory behaviors.