Final answer:
A decrease in the amount of prolactin-inhibiting hormone leads to an increased release of prolactin, which stimulates milk production by the mammary glands after childbirth. Prolactin levels are balanced by both inhibitory and stimulatory factors from the hypothalamus and influenced by other hormones during pregnancy.
Step-by-step explanation:
A decrease in the amount of prolactin-inhibiting hormone (PIH) results in increased release of prolactin (PRL) from the anterior pituitary gland. Prolactin is responsible for stimulating milk production in the mammary glands following childbirth.
PIH, which is identified as dopamine, acts as an inhibitor for prolactin release. High levels of PIH will suppress prolactin secretion, whereas decreased levels will lessen this inhibition, allowing for increased prolactin secretion. This can lead to excess production of prolactin, resulting in conditions such as amenorrhea, galactorrhea, and an enlargement of the breasts.
It is important to note that prolactin levels are influenced by a complex set of hormonal signals, including prolactin-releasing hormone (PRH) from the hypothalamus, and other hormones like estrogen, progesterone, and placental hormones during pregnancy that can also affect prolactin-mediated milk synthesis.