Current Insights in Prolactin Signaling and Ovulatory Function

Abstract

Prolactin (PRL) is a pleiotropic hormone released from lactotrophic cells of the anterior pituitary gland that also originates from extrapituitary sources and plays an important role in regulating lactation in mammals, as well as other actions. Acting in an endocrine and paracrine/autocrine manner, PRL regulates the hypothalamic–pituitary–ovarian axis, thus influencing the maturation of ovarian follicles and ovulation. This review provides a detailed discussion of the current knowledge on the role of PRL in the context of ovulation and ovulatory disorders, particularly with regard to hyperprolactinemia, which is one of the most common causes of infertility in women. Much attention has been given to the PRL structure and the PRL receptor (PRLR), as well as the diverse functions of PRLR signaling under normal and pathological conditions. The hormonal regulation of the menstrual cycle in connection with folliculogenesis and ovulation, as well as the current classifications of ovulation disorders, are also described. Finally, the state of knowledge regarding the importance of TIDA (tuberoinfundibular dopamine), KNDγ (kisspeptin/neurokinin B/dynorphin), and GnRH (gonadotropin-releasing hormone) neurons in PRL- and kisspeptin (KP)-dependent regulation of the hypothalamic–pituitary–gonadal (HPG) axis in women is reviewed. Based on this review, a rationale for influencing PRL signaling pathways in therapeutic activities accompanying ovulation disorders is presented.

The Effect of Prolactin on Gene Expression and the Secretion of Reproductive Hormones in Ewes during the Estrus Cycle

“…Endocrine pathways play an essential role in the menstrual cycle [44], throughout which hormone levels fluctuate [45], regulating estrus production [46] and ovulation [47]. Our study showed that PRL inhibition significantly increased the concentrations of GnRH, FSH, and E2 as well as the number of small follicles in the proestrus stage and increased the concentrations of GnRH and E2 in the estrus stage.…”

“…Our study showed that PRL inhibition significantly increased the concentrations of GnRH, FSH, and E2 as well as the number of small follicles in the proestrus stage and increased the concentrations of GnRH and E2 in the estrus stage. A high PRL concentration suppresses the hypothalamic gonadotropin-releasing hormone, which plays a pivotal role in reproduction by stimulating the synthesis and secretion of LH and FSH [47]. Upon FSH stimulation, a cohort of small antral follicles begins the gonadotropin-dependent development phase of recruited follicles [48].…”