Which of the following hormones is NOT typically involved in regulating the menstrual cycle?

Prolactin is indeed the hormone that is least involved in the regulation of the menstrual cycle. The menstrual cycle is primarily regulated by hormones such as luteinizing hormone (LH), estrogen, and progesterone. LH plays a crucial role in triggering ovulation and stimulating the production of estrogen and progesterone from the ovaries. Estrogen is responsible for the development and maintenance of female reproductive structures and the regulation of the cycle phases. Progesterone is important for preparing the endometrium for potential pregnancy after ovulation.

In contrast, although prolactin is involved in lactation and breast development, its role in menstrual cycle regulation is minimal. Elevated prolactin levels can lead to menstrual irregularities and may inhibit ovulation, but it does not play a direct role in the hormonal feedback loops that regulate the menstrual cycle phases.