USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

During pregnancy, what effect does high progesterone levels have on prolactin release?

1. Stimulate prolactin release

2. Inhibit prolactin release

3. No effect on prolactin release

4. Induce LH surge

The correct answer is: Inhibit prolactin release

During pregnancy, high progesterone levels play a significant role in the regulation of various hormones, including prolactin. Progesterone, primarily produced by the corpus luteum in early pregnancy and later by the placenta, has an inhibitory effect on the hypothalamic-pituitary axis. This inhibition specifically affects the release of prolactin. Prolactin is important for lactation and is typically regulated by both stimulating and inhibitory signals. The primary inhibitor of prolactin release is dopamine, released from the hypothalamus. During pregnancy, as progesterone levels rise, they increase the inhibitory influence on the release of prolactin from the anterior pituitary gland, leading to a decrease in its secretion. This modulation helps ensure that while the body prepares for milk production, the actual release of prolactin is suppressed until after childbirth when progesterone levels drop, and prolactin can rise in response to the suckling stimulus. Understanding the interaction between progesterone and prolactin is crucial for grasping how hormonal changes orchestrate the complex physiological processes involved in pregnancy and lactation.