What effect does prolactin have in mammals?

Prolactin is a hormone produced by the anterior pituitary gland that plays a pivotal role in lactation and milk production in mammals. When a female mammal gives birth, prolactin levels increase to stimulate the mammary glands, promoting the production of milk. This hormone is essential not only for initiating lactation but also for maintaining milk supply throughout the nursing period.

In addition to its role in milk production, prolactin has various functions in reproduction, immune response, and behavioral aspects, but its primary and most well-known function is directly linked to lactation. Understanding the significance of prolactin helps to comprehend its impact on mammalian reproductive physiology, particularly in females. The other options relate to different hormones or biological processes; for example, growth is mainly stimulated by growth hormone, metabolism regulation is primarily managed by thyroid hormones and insulin, and the stress response is largely influenced by cortisol and adrenaline. Therefore, the specific role of prolactin in controlling milk production stands out as the defining function of this hormone among the choices provided.