Which hormone is primarily responsible for stimulating Wolffian duct differentiation?

Testosterone is the hormone primarily responsible for stimulating the differentiation of Wolffian ducts, which are crucial in the development of male reproductive structures. During male embryonic development, the presence of testosterone leads to the development of male internal genitalia, including structures such as the epididymis, vas deferens, and seminal vesicles.

The Wolffian ducts are initially present in both male and female embryos, but in the absence of testosterone, they will regress in females. The action of testosterone on the Wolffian ducts is key to establishing male sexual differentiation. This process is part of a broader chain of events influenced by other hormones, but testosterone is central to promoting the growth and maturation of these ducts in male fetuses.

In contrast, other hormones like estrogen, prolactin, and progesterone play different roles in reproductive physiology and do not directly stimulate Wolffian duct differentiation. Estrogen is primarily involved in female sexual development and the menstrual cycle, prolactin focuses on lactation and maternal behaviors, while progesterone is crucial for maintaining pregnancy and preparing the endometrium for implantation, rather than for male duct development. Thus, testosterone's specific role in promoting Wolffian duct differentiation makes it the correct answer.