Prolactin delays gonadotrophin-induced ovulation and down-regulates expression of plasminogen-activator system in ovary

Current Insights in Prolactin Signaling and Ovulatory Function

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 relationship between serum prolactin concentration and pregnancy outcome in women with unexplained recurrent miscarriage

The role of prolactin in early pregnancy is controversial. The aim of this study was to evaluate the relationship between serum prolactin concentration and the risk of miscarriage in women with unexplained recurrent miscarriage (RM). A series of 174 women with unexplained RM, who had serum prolactin concentrations measured from January 2000 to September 2009 at the Recurrent Miscarriage Clinic in Royal Hallamshire Hospital in Sheffield, were included in this study. Among the 174 patients with unexplained RM, 40 patients did not conceive during the study period, 9 were lost to follow-up and 125 patients conceived again. Patients who did not conceive were significantly older than those who conceived (p < 0.05, OR: 1.08, 95% CI: 1.03-1.13). Among those who conceived again, the pregnancy outcome data were available for analysis in 109 patients. Those who miscarried were older (p < 0.05, OR: 1.1, 95% CI: 1.01-1.22) and had significantly lower serum prolactin concentrations (p < 0.05, adjusted OR: 0.99, 95% CI: 0.97-0.99) after adjustment has been made for age, than those who had a live birth. Lower basal serum prolactin concentrations were associated with an increased risk of miscarriage in a subsequent pregnancy in women with unexplained RM.

Production and binding of endothelin-2 (EDN2) in the rat ovary: endothelin receptor subtype A (EDNRA)-mediated contraction

Endothelin-2 (EDN2)-mediated contraction has been proposed as a final mechanical signal facilitating ovulation. The objectives herein were to determine (1) whether ovarian endothelins were increased before ovulation; (2) whether a specific endothelin-converting enzyme (ECE) was mediating their production; (3) which receptor was facilitating ovarian contraction; and (4) whether receptor-specific antagonism affected ovulation. Follicular development was induced in immature rats with 10 IU pregnant mare serum gonadotrophin (PMSG) and the ovulatory cascade was initiated 48 h later with 10 IU human chorionic gonadotrophin (hCG). In Experiment 1, an immunoassay revealed that the ovarian concentration of endothelin peptide was increased 7-fold 12 h after hCG when compared with 48 h after PMSG (P < 0.05). In Experiment 2, real-time PCR indicated that mRNA for Ece1, but not Ece2, was increased in granulosa cells collected 12 h after hCG when compared with those collected before the ovulatory stimulus (P < 0.05). In Experiment 3, isometric tension analysis revealed that the contractile effect of EDN2 was mediated by endothelin receptor A (EDNRA), not B (EDNRB). In Experiment 4, no effect was observed on the rate of ovulation when rats were treated with an antagonist specific to EDNRA (BQ123) or EDNRB (BQ788), or when mice were treated with BQ123, BQ788 or BQ123 + BQ788. In conclusion, endothelin peptide is produced before ovulation and the contractile action of EDN2 within the ovary is facilitated via EDNRA. In addition, findings of this study indicate synergistic interactions among contractile factors affect ovulatory outcome, while the role of EDNRB alone in the process of ovulation requires further investigation.

Expression of prolactin receptors in rat reproductive tissues during periovulatory prolactin imbalance

Indirect immunoperoxidase technique in combination with cytophotometry showed that prolactin imbalance in the periovulatory period is characterized by considerable changes in the expression of prolactin receptors in uterine glands and endometrial stroma (but not in the myometrium) and in the pituitary gland and hypothalamus, while receptor compartmentalization pattern remains unchanged.

Expression of the steroidogenic acute regulatory protein and luteinizing hormone receptor and their regulation by tumor necrosis factor alpha in rat corpora lutea

Expression of both mRNA and protein of the steroidogenic acute regulatory protein (StAR), in correlation with progesterone (P) production and LH receptor (LHR) mRNA expression, was studied in the corpora lutea (CL) of gonadotropin-induced-pseudopregnant and pregnant rats at various stages of CL development. Immature female rats, 21-22 days old, were injected s.c. with 20 IU eCG to stimulate follicle growth and then with 20 IU hCG 48 h later to induce ovulation. The ovaries were removed at various stages of CL development; either CL were isolated and snap frozen for total RNA analysis, or whole ovaries were fixed in Bouin's fluid for paraffin sectioning. The results of in situ hybridization, immunohistochemistry, and Northern blotting showed that the increase in StAR mRNA and protein expression was well correlated with the increase in serum P concentration. StAR expression was restricted to the luteal cells or theca cells in antral follicles. Both StAR mRNA and protein in the CL of pseudopregnant rats increased steadily on Day 1 and Day 4, reached highest levels on Day 4, and then dropped sharply on Day 8 when luteolysis takes place. LHR mRNA content was high on Day 1 but dropped significantly on Day 2. LHR mRNA increased to high levels on Day 4 and 8 and then declined on Day 12. StAR mRNA and protein levels in the CL of pregnant rats were high during early luteal development (Day 2, 4), increased even further on Day 9, and decreased on Day 13 when luteolysis takes place. It is therefore suggested that the expression of StAR coincides well with the capacity of P production in the CL and that StAR expression can be used as a functional "marker" of CL development. To study the possible effect of cytokines on StAR expression, pseudopregnant rats on Day 5 were injected s.c. with 10 IU hCG plus 20 microg prolactin (PRL), with or without 500 IU tumor necrosis factor alpha (TNFalpha) 30 min later. TNFalpha significantly inhibited hCG/PRL-induced StAR and LHR mRNA expression at 1 and 3 h post-TNFalpha. It is suggested that the luteolytic effect of TNFalpha may be mediated by its direct inhibition on StAR expression or by an indirect decrease in LHR expression.

Prolactin regulation of tissue type plasminogen activator and plasminogen activator inhibitor type-I gene expression in eCG-primed rat granulosa cells in culture

The present study was designed to investigate the effect of prolactin (PRL) on plasminogen activator inhibitor-I (PAI-I) and tissue type plasminogen activator (tPA) gene expression in eCG-primed granulosa cells in vitro. At 46 h after the hormone treatment, ovaries were removed, and granulosa cells were prepared for culture. Cells were incubated for various times in serum-free medium in the presence or absence of LH and PRL alone or in combination. tPA and PAI-I activities in the media were assayed by fibrin overlay and reverse fibrin autograph, respectively. Cytoplasmic RNA from granulosa cells was prepared using the NP-40 method and was assayed for PAI-I and tPA mRNA levels. We demonstrated the following. 1) PRL increased PAI-I mRNA production in cultured granulosa cells. Inclusion of LH with PRL had a synergistic effect on increasing PAI-I mRNA levels. After 48-h culture, 3-fold increases in PAI-I mRNA levels were seen with LH in combination with PRL as compared with PRL alone. The synergistic increase in PAI-I mRNA levels occurred in a dose- and time-dependent manner. 2) The increase in PAI-I mRNA synthesis by PRL alone, or by PRL in combination with LH, was well correlated with the changes in PAI-I activity and antigen levels in the conditioned media. 3) PRL in the culture also dramatically decreased LH-induced tPA mRNA and activity in a dose- and time-dependent fashion. The decrease in the tPA activity by PRL was also correlated with an increase in the amount of PA-PAI-I complexes in the cell-conditioned media. 4) In situ hybridization of tPA and PAI-I mRNAs in the cultured granulosa cells also showed that PRL was capable of enhancing PAI-I mRNA while diminishing tPA mRNA production induced by LH. This suggests that the dose- and time-dependent decrease in the gonadotropin-induced tPA activity in the culture by the presence of PRL may be due to decreasing tPA mRNA synthesis on one hand and to neutralization of the tPA activity by the increased PAI-I activity on the other.