Prolactin inhibits the steroidogenesis in midfollicular phase human granulosa cells cultured in a chemically defined medium

Hyperprolactinaemia - a problem in patients from the reproductive period to the menopause

Hyperprolactinaemia especially affects women in reproductive age (90/100,000) but also often is diagnosed in menopause age and leads to disturbances in functioning of LH-RH neurons and, as a consequence, to a decrease of FSH and LH, which causes inhibition of oestradiol production. Prolactin is a peptide hormone, phylogenetically one of the oldest, stimulating cells of various organs, which is produced and secreted mainly by lactotrophic acidophilic cells of the anterior lobe of the pituitary. It influences the increase in the mass of the mammary glands, and stimulation and maintenance of lactation after delivery. There are a number of factors apart of pregnancy, delivery, and lactation than can influence secretion of the hormone in other physiological and pathological circumstances, like high-protein diet, stress, REM sleep, or neoplastic tumours, inflammatory diseases, chronic systematic diseases, thyroid hormonal changes, and drug intake. The purpose of this review is to summarise the current knowledge regarding the proper diagnosis and possible influence of hyperprolactinaemia on fertility and menopause symptoms and current treatment methods.

Prolactin inhibits oocyte release after gonadotropin stimulation in the rat: Putative mechanism involving ovarian production of beta-endorphin and prostaglandin

OBJECTIVE

To evaluate whether prolactin (PRL) is able to inhibit ovulation induced with exogenous gonadotropins in the rat and whether this effect could be mediated by the ovarian production of beta-endorphin, prostaglandin, and nitric oxide (NO).

DESIGN

Controlled in vivo and in vitro experiments.

SETTING

Academic research laboratories.

ANIMAL(S)

Immature female rats undergoing ovulation induction with equine gonadotropins and hCG.

INTERVENTION(S)

Prolactin (100 or 200 microg), PRL + the opioid antagonist naloxone (200 microg each), or placebo were injected SC 4 hours after hCG administration for ovulation induction. In the in vitro experiments, isolated preovulatory ovaries were incubated with or without PRL in a final concentration of 100 or 200 ng/mL.

MAIN OUTCOME MEASURES(S)

Number of oocytes ovulated in vivo, ovarian beta-endorphin, PGE(2) and NO(2)(-)/NO(3)(-) release, and NO synthase activity in vitro.

RESULT(S)

Prolactin reduced significantly the number of oocytes ovulated at the doses of 100 and 200 microg, and this effect was partially reversed by naloxone administration together with 200 mug PRL. PRL also induced a twofold increase in the ovarian release of beta-endorphin and a threefold decrease in the ovarian production of PGE(2). Ovarian NO synthase activity and the concentrations of NO(2)(-)/NO(3)(-) in the incubation medium were not modified by PRL.

CONCLUSION(S)

Prolactin is able to reduce the number of oocytes released and modulate ovarian beta-endorphin and PGE(2) release, which may account for its peripheral anovulatory effects. This local effect of PRL could interfere in the process of ovulation induction by exogenous gonadotropins.

Effect of prolactin on follicle-stimulating hormone receptor binding and progesterone production in cultured porcine granulosa cells

OBJECTIVE

To determine the effect of prolactin (PRL) on follicle-stimulating hormone receptor (FSH-R) binding and progesterone (P) production in cultured porcine granulosa cells.

DESIGN

Controlled experiment.

SETTING

Academic research laboratory.

INTERVENTION(S)

Immature granulosa cells were cultured in a serum-free medium. All cell populations were supplemented with porcine (p) FSH and cultured in the absence or presence of ovine (o) PRL.

MAIN OUTCOME MEASURE(S)

Specific pFSH-R binding and P in medium.

RESULT(S)

In the control cells, FSH-R binding increased 31-fold and P production increased 700-fold by day 4. Physiologic levels of oPRL potentiated the action of pFSH and resulted in a further 50% increase in pFSH-R binding and P production by day 4 over that in controls. In contrast, higher concentrations of oPRL blocked the rise in both pFSH-R binding and P production. The alteration in pFSH-R binding was associated with a change in FSH-R number.

CONCLUSION(S)

Physiologic levels of PRL amplify the stimulatory effects of FSH on the acquisition of the FSH-R and P production in cultured granulosa cells. Higher concentrations of PRL cause a decrease in FSH-R binding and P production. Prolactin may act as a "co-gonadotropin" and fine-tune the process of folliculogenesis by altering the acquisition of granulosa FSH receptors.

Blockage of gonadotropin-induced first ovulation caused by thyroidectomy and its possible mechanisms in rats

To determine the role of the thyroid gland on the ovarian functions during the initiation process of puberty, we examined the effects and its mechanisms of hypothyroidism on the first ovulation induced by equine chorionic gonadotropin (eCG) in immature female rats. Animals were thyroidectomized on day 22 and were injected with 5 IU of eCG on day 26 to induce the first ovulation on day 29. The number of antral follicles that secrete inhibin and the ovarian weight were significantly increased in thyroidectomized rats (Tx rats) 48 h after eCG treatment compared with those in non-Tx rats. However, thyroidectomy (Tx) significantly suppressed the rates of ovulating animals on day 29. The blockage of ovulation in Tx rats was recovered by administration of human chorionic gonadotropin or luteinizing hormone (LH)-releasing hormone (LHRH) on day 28. Inhibition of serum LH (not follicle-stimulating hormone) levels induced by Tx was almost restored to control levels by injection of LHRH. A significant increment in prolactin levels in Tx rats was also observed on day 28. The present data indicate that Tx before puberty in female rats causes the blockage of the first ovulation and that the inhibitory effects on ovulation are mainly due to the reduction in the preovulatory LH surge, which is partially mediated through an inhibition of LHRH action on the secretion of LH.

Prolactin (PRL) and its receptor: actions, signal transduction pathways and phenotypes observed in PRL receptor knockout mice

PRL is an anterior pituitary hormone that, along with GH and PLs, forms a family of hormones that probably resulted from the duplication of an ancestral gene. The PRLR is also a member of a larger family, known as the cytokine class-1 receptor superfamily, which currently has more than 20 different members. PRLRs or binding sites are widely distributed throughout the body. In fact, it is difficult to find a tissue that does not express any PRLR mRNA or protein. In agreement with this wide distribution of receptors is the fact that now more than 300 separate actions of PRL have been reported in various vertebrates, including effects on water and salt balance, growth and development, endocrinology and metabolism, brain and behavior, reproduction, and immune regulation and protection. Clearly, a large proportion of these actions are directly or indirectly associated with the process of reproduction, including many behavioral effects. PRL is also becoming well known as an important regulator of immune function. A number of disease states, including the growth of different forms of cancer as well as various autoimmune diseases, appear to be related to an overproduction of PRL, which may act in an endocrine, autocrine, or paracrine manner, or via an increased sensitivity to the hormone. The first step in the mechanism of action of PRL is the binding to a cell surface receptor. The ligand binds in a two-step process in which site 1 on PRL binds to one receptor molecule, after which a second receptor molecule binds to site 2 on the hormone, forming a homodimer consisting of one molecule of PRL and two molecules of receptor. The PRLR contains no intrinsic tyrosine kinase cytoplasmic domain but associates with a cytoplasmic tyrosine kinase, JAK2. Dimerization of the receptor induces tyrosine phosphorylation and activation of the JAK kinase followed by phosphorylation of the receptor. Other receptor-associated kinases of the Src family have also been shown to be activated by PRL. One major pathway of signaling involves phosphorylation of cytoplasmic State proteins, which themselves dimerize and translocate to nucleus and bind to specific promoter elements on PRL-responsive genes. In addition, the Ras/Raf/MAP kinase pathway is also activated by PRL and may be involved in the proliferative effects of the hormone. Finally, a number of other potential mediators have been identified, including IRS-1, PI-3 kinase, SHP-2, PLC gamma, PKC, and intracellular Ca2+. The technique of gene targeting in mice has been used to develop the first experimental model in which the effect of the complete absence of any lactogen or PRL-mediated effects can be studied. Heterozygous (+/-) females show almost complete failure to lactate after the first, but not subsequent, pregnancies. Homozygous (-/-) females are infertile due to multiple reproductive abnormalities, including ovulation of premeiotic oocytes, reduced fertilization of oocytes, reduced preimplantation oocyte development, lack of embryo implantation, and the absence of pseudopregnancy. Twenty per cent of the homozygous males showed delayed fertility. Other phenotypes, including effects on the immune system and bone, are currently being examined. It is clear that there are multiple actions associated with PRL. It will be important to correlate known effects with local production of PRL to differentiate classic endocrine from autocrine/paracrine effects. The fact that extrapituitary PRL can, under some circumstances, compensate for pituitary PRL raises the interesting possibility that there may be effects of PRL other than those originally observed in hypophysectomized rats. The PRLR knockout mouse model should be an interesting system by which to look for effects activated only by PRL or other lactogenic hormones. On the other hand, many of the effects reported in this review may be shared with other hormones, cytokines, or growth factors and thus will be more difficult to study. (ABSTRACT TRUNCATED)

Mechanism of anovulation in hyperprolactinemic amenorrhea determined by pulsatile gonadotropin-releasing hormone injection combined with human chorionic gonadotropin

OBJECTIVE

To clarify the mechanism of anovulation in hyperprolactinemic anovulatory women by subcutaneous (SC) pulsatile GnRH injection.

DESIGN

Prospective clinical study.

SETTING

Studies were made on at the Department of Obstetrics and Gynecology, the University of Tokushima, School of Medicine.

PATIENTS

Six hyperprolactinemic (group 1) and 7 normoprolactinemic (group 2) anovulatory patients were studied.

INTERVENTIONS

After examinations of pulsatile secretion of LH, the GnRH test, thyrotropin-releasing hormone test and estrogen test, pulsatile GnRH treatment (20 micrograms/2 hours SC) was performed. Two protocols were tested on each patient. In the non-hCG protocol, GnRH treatment was continued until ovulation. In the hCG protocol, 5,000 IU of hCG was injected to induce ovulation when follicles were fully mature.

MAIN OUTCOME MEASURE

The rates of follicular maturation and ovulation, serum E2 and P in the two groups.

RESULTS

Pulsatile LH secretion was impaired in both groups. LH release 48 hours after estrogen injection was impaired in group 1 but not in group 2. Follicles matured on pulsatile GnRH treatment in all cycles in both groups. However, with the non-hCG protocol, ovulation occurred in only 17% of group 1, but in 89% of group 2. With the hCG protocol ovulation occurred in all cycles in both groups.

CONCLUSIONS

The main cause of anovulation is impaired gonadotropin pulsatility and derangement of the estrogen-positive feedback effect on LH secretion in hyperprolactinemic patients, their ovarian response to gonadotropin being well maintained. Subcutaneous pulsatile GnRH therapy combined with hCG can be used as an alternative to bromocriptine treatment for induction of ovulation in these patients.

Follicular development, oocyte viability and recovery in relation to follicular steroids, prolactin and glycosaminoglycans throughout the estrous period in superovulated heifers with a normal LH surge, no detectable LH surge, and progestin inhibition of LH surge

Estrous cycles of heifers (n = 137) were synchronized with prostaglandin (PGF2 alpha) and follicular development stimulated with follicle stimulating hormone. Twenty-eight animals were administered Norgestomet implants 12 hr prior to the initial PGF2 alpha injection to suppress the LH surge that initiates ovulation. Animals were ovariectomized every 12 hr after the initial PGF2 alpha (7-9/time, 12-108 hr and at 192 and 240 hr post PGF2 alpha) and divided into three treatment groups to consist of: 1) animals exhibiting a normal luteinizing hormone (LH) surge (n = 86), 2) animals in which no LH surge was detected (n = 23), and 3) suppression of the LH surge via Norgestomet implants (72-108 hr, n = 28). Follicular diameter was measured and follicular fluid was collected for analysis of prolactin, estradiol, progesterone and glycosaminoglycan concentrations. Progesterone concentrations were increased in animals exhibiting an LH surge as compared to animals in which no LH surge was detected; primarily in large follicles (> 8 mm diameter) after the LH surge. Animals not exhibiting an LH surge also had increased follicular progesterone concentrations compared to Norgestomet-implanted animals (242.3 +/- 36.3 vs 86.7 +/- 6.4 ng/ml, respectively, P < .01), indicating some LH stimulation. Follicular estradiol in animals exhibiting an LH surge increased up to the time of LH surge detection and then declined whereas animals with no LH surge detected had follicular estradiol concentrations that declined after the PGF2 alpha injection. No differences were noted between those that did not exhibit an LH surge or in which the LH surge was suppressed with Norgestomet in relation to follicular estradiol concentrations. Follicular estradiol concentrations increased with follicular size in all treatment groups (P < .01). Follicular concentrations of prolactin were increased in small follicles (P < .05; < or = 4 mm diameter) and follicular prolactin increased from 12 to 36 hr post PGF2 alpha injection, then declined after the LH surge. Follicular glycosaminoglycan concentrations decreased with increases in follicular size (P < .01) and were higher in animals that did not exhibit an LH surge (P < .01). No differences in follicular glycosaminoglycans were noted between Norgestomet-implanted animals and those not exhibiting an LH surge. In the animals representing days 4 and 6 of the subsequent estrous cycle (192 and 240 hr post PGF2 alpha), numbers of small-sized follicles were increased. Follicular progesterone and estradiol concentrations were related to atretic large follicles unovulated from the prior estrus and a new wave of growth in small and medium follicles.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of prolactin on murine in vitro fertilization and embryo development

Elevated levels of serum and follicular fluid prolactin occur in women undergoing ovulation induction with both clomiphene citrate and gonadotropin therapy. Prolactin's effect on oocyte fertilization and embryo cleavage has not been fully characterized. Using a murine model, we investigated the effect of prolactin on in vitro fertilization and subsequent embryo cleavage in media containing 150, 400, and 600 ng/ml purified mouse prolactin. No difference was found in fertilization rates when compared with control rates. Culture of both in vivo and in vitro fertilized two-cell embryos in murine prolactin at 150, 400, and 600 ng/ml showed no significant difference in blastocyst, morula, or embryo degeneration rates when compared with control rates. An assay for binding of murine prolactin to spermatozoa, oocytes, and the embryo at various cleavage stages revealed no specific murine prolactin binding. These in vitro experimental results fail to show a role for murine prolactin in effecting mature oocyte fertilization or subsequent embryo cleavage. The lack of binding of murine prolactin to the gametes and early developing embryo supports the in vitro findings.

The metoclopramid-provocation test for prediction of transient hyperprolactinemia during cycle stimulation

The predictive value of the metoclopramid-provocation test to detect transient hyperprolactinemia during cycle stimulation was assessed. Patients developing hyperprolactinemia during cycle stimulation showed a significantly higher PRL response to the metoclopramid-provocation test before cycle stimulation. The current study confirms previous reports that hyperprolactinemia during cycle stimulation can interfere with follicular and oocyte maturation. The use of the metoclopramid-test can detect an enhanced responsiveness to PRL stimulators and offers the possibility of treatment during cycle stimulation.

The influence of transient hyperprolactinemia on hormonal parameters, oocyte recovery, and fertilization rates in in vitro fertilization

A detrimental effect of transient elevation of plasma prolactin (PRL) during in vitro fertilization (IVF) has not been proven; however, treatment with a dopamine agonist has been suggested. The present study was undertaken to determine if transient, midcycle hyperprolactinemia exerted a deleterious effect on the number of oocytes retrieved or on fertilization of oocytes in vitro. Fifty-three infertile patients with midcycle hyperprolactinemia (PRL greater than 20 micrograms/liter) during ovarian hyperstimulation for IVF were compared with 53 matched controls who remained normoprolactinemic. Mean (+/- SE) serum PRL levels on the day after hCG were significantly higher in the study group (29.5 +/- 1 micrograms/liter) than in the control (13.1 +/- 0.5 microgram/liter) (P less than 0.0005), whereas the mean estradiol (E2) concentrations on the same day were not significantly different (4822 +/- 287 and 4492 +/- 269 pmol/liters, respectively). Fertilization rates (72 +/- 4 and 70 +/- 4%, respectively) and the mean number of oocytes recovered (4.2 +/- 0.3 and 3.7 +/- 0.3, respectively) did not differ between the two groups. No correlation was observed between serum PRL and E2 levels, fertilization rates, or the number of oocytes retrieved in either group. Eleven patients with elevated PRL levels as a result of ovarian hyperstimulation were treated with 2.5 mg bromocriptine daily during the next IVF cycle. Serum PRL levels were significantly lower in the treated (5.6 +/- 1.8 micrograms/liter) than in the untreated cycles (35.6 +/- 3.1 micrograms/liter) (P less than 0.0005), whereas serum E2 concentrations did not differ.(ABSTRACT TRUNCATED AT 250 WORDS)