Which hypothalamic hormone inhibits the release of prolactin?

The hypothalamic hormone that inhibits the release of prolactin is indeed the Prolactin Inhibiting Factor (PIF). This hormone primarily functions as a regulator of prolactin secretion by acting on the anterior pituitary gland. Prolactin is responsible for lactation and other reproductive functions, and its secretion is primarily regulated by inhibitory feedback from PIF, which is now identified as dopamine. When dopamine levels are adequate, prolactin secretion is suppressed.

In contrast, the other hormones mentioned do not serve this specific inhibitory role. Gonadotropin Releasing Hormone (GnRH) primarily stimulates the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary. Growth Hormone Releasing Hormone (GHRH) stimulates the release of growth hormone, while Corticotropin Releasing Hormone (CRH) promotes the secretion of adrenocorticotropic hormone (ACTH). Therefore, while these hormones have critical functions in the endocrine system, they do not inhibit prolactin release, making PIF the correct answer for this question.