Prolactin is a polypeptide hormone of 199 amino acids weighing 23 kDa produced by the lactotroph cells of the anterior pituitary which make up 20%. Its main action is to promote lactation, since the act of sucking the mother's breast by the baby increases the secretion of prolactin and it stimulates lactogenesis.
This therefore guarantees a normal lactation adapted to the needs of the baby. There are, however, many other effects of prolactin, which is also produced by males. Prolactin is the only pituitary hormone that suffers constant inhibitory tone from the hypothalamus.
This has been demonstrated by the interruption of communication between the pituitary and the hypothalamus, when the secretion of prolactin increases, while that of other pituitary hormones decreases. However, the regulation of prolactin secretion remains very complex and is determined by different situations and by different substances, still much studied.
However, some substances have a stronger action, being dopamine, for example, the most powerful inhibitory factor. On the contrary, certain situations such as pregnancy and breastfeeding make prolactin levels higher. The Seasonality of prolactin in birds and mammals study, published in the Journal of experimental zoology.
Part A, Ecological and integrative physiology, said: "In most animals, annual rhythms in environmental cues and internal programs regulate seasonal physiology and behavior. Prolactin, an evolutionarily ancient hormone, serves as a molecular correlate of seasonal timing in most species.
Prolactin is highly pleiotropic with a wide variety of well-documented physiological effects;in a seasonal context prolactin is known to regulate annual changes in pelage and molt.While short-term homeostatic variation of prolactin secretion is under the control of the hypothalamus, long-term seasonal rhythms of prolactin are programmed by endogenous timers that reside in the pituitary gland.
The molecular basis of these rhythms is generally understood to be melatonin dependent in mammals.Prolactin rhythmicity persists for several years in many species, in the absence of hypothalamic signaling. Such evidence in mammals has supported the hypothesis that seasonal rhythms in prolactin derive from an endogenous timer within the pituitary gland that is entered by external photoperiod.
In this review, we describe the conserved nature of prolactin signaling in birds and mammals and highlight its role in regulating multiple diverse physiological systems. The review will cover the current understanding of the molecular control of prolactin seasonality and propose a mechanism by which long-term rhythms may be generated in amniotes."