The main function of the Prolactin hormone is to
A. Influence the activity of the thyroid gland
B. Control development of graffian follicles
C. Initiate and maintain secretion of milk by the mammary gland
D. Cause ejection of milk

Hint: Prolactin, also called as luteotropic hormone (LTH) or luteotropin, is a protein hormone produced by the pituitary gland of mammals, that acts with other hormones to initiate secretion of milk by the mammary glands.

Complete answer: Progesterone stimulates the development of the duct system. During pregnancy, these hormones enhance further development of the mammary glands.
1. Prolactin from the anterior pituitary stimulates the production of milk within the glandular tissue, and oxytocin causes the ejection of milk from the glands. The pituitary gland sits directly behind the nasal bridge in a protective boney structure called the “sella turcica” and it is connected to the hypothalamus by the infundibular stalk.
2. The pituitary gland is structurally divided into anterior and posterior regions. The anterior pituitary is capable of producing and secreting its own hormones, compared to the posterior pituitary gland which acts more as a conduit for presynthesized hormones by the hypothalamus.
3. During pregnancy, estrogen, and progesterone are found at elevated levels and they function to promote the growth of mammary tissue.
4. Estrogen largely does not impact prolactin’s production or secretion. The most potent stimulator for prolactin synthesis interestingly is suckling or nipple stimulation.
5. Prolactin contributes to hundreds of physiologic functions, but the two primary responsibilities are milk production and the development of mammary glands within breast tissues. Prolactin promotes the growth of mammary alveoli, which are the components of the mammary gland, where the actual production of milk occurs.
6. Prolactin stimulates the breast alveolar epithelial cells to synthesize milk components, including lactose, casein, and lipids. The prolactin receptors are down-regulated on mammary glandular tissue during periods of elevated progesterone levels ( during pregnancy).
7. After delivery, the serum progesterone level drops, allowing for the up-regulation of prolactin receptors on the mammary alveolar cells, therefore enabling lactogenesis.

So, the correct answer is “Option C”.

Note: Prolactin deficiency can be secondary to other etiologies that primarily affect the anterior pituitary. The anterior pituitary function to produce hormones can become impaired due to mass effect (i.e., craniopharyngiomas) or infections such as tuberculosis and histoplasmosis.
Infiltrative disease processes like sarcoidosis and hemochromatosis are also hyperprolactinemia etiologies.