While functions of the hormones are described as being somewhat specific, most hormones function in concert with one another. Most hormones with the exception of prolactin stimulate their target tissues to release other hormones.
Prolactin is involved in the development of the mammary gland and initiation of milk secretion.
Somatotropin and prolactin are directly required for normal development and growth of the mammary gland, and also serve to indirectly synergize the effects of ovarian hormones on mammary tissue. To achieve the increase in milk production, the hormone must be injected daily or biweekly depending on the preparation. As of 1994, recombinant somatotropin is available commercially in the United States. Injections are to be given every 14 days beginning at 60 days postpartum. Vasopressin serves to maintain blood volume through it's effects on the kidney.