Amniotic fluid prolactin and fetal lung maturation

Characterization of a rat uterine cell line, U(III) cells: prolactin (PRL) expression and endogenous regulation of PRL-dependent genes; estrogen receptor beta, alpha(2)-macroglobulin, and decidual PRL involving the Jak2 and Stat5 pathway

Decidualization of endometrial stroma in the rat induces the expression and secretion of rat decidual PRL (rdPRL). Recently, we have generated a nontransformed rat uterine stromal cell line (U(III)) that decidualizes spontaneously in culture. In this report, we have established by immunocytochemistry, RT-PCR, Western blot analysis, labeled amino acid incorporation and RIA that these cells express the rat PRL messenger RNA as well as synthesize and secrete PRL. We have also cloned by RT-PCR a 403-bp complementary DNA fragment whose sequence is identical with that of rat pituitary PRL. In addition, U(III) cells express the PRL receptor (PRL-R) long form, all the components involved in the PRL signal transduction pathway, estrogen receptor beta (ER beta) and alpha(2)-macroglobulin (alpha(2)-MG), which are known to be PRL-regulated genes. However, when U(III) cells were treated with PRL, no regulation of these genes was observed. Moreover, in these cells, the PRL signaling components: the tyrosine kinase Jak2 and the transcription factor Stat5 were endogenously phosphorylated and their phosphorylation states were not enhanced in the presence of exogenous PRL. To examine whether the endogenously secreted PRL affects the expression of PRL-regulated genes, U(III) cells were treated with either an anti-PRL receptor antibody or a Jak2 inhibitor, AG490. The anti-PRL receptor antibody decreased alpha(2)-MG expression. AG490 inhibited Jak2 and Stat5 phosphorylation, prevented Stat5 binding to its DNA consensus sequence, and also caused a dose-dependent down-regulation of alpha(2)-MG and ER beta expression. In contrast, AG490 enhanced PRL mRNA levels. In summary, we have established that the U(III) stromal cells of uterine origin produce PRL. Furthermore, we have shown for the first time that decidual PRL may act locally to activate the Jak2/Stat5 pathway and up-regulate important genes involved in decidual growth and placentation.

Paracrine/autocrine control of female reproduction

Neuropeptides, growth factors and cytokines are expressed in reproductive organs and tissues, where they interact with afferent endocrine messages to modulate cell proliferation and differentiation, local hormone secretion and vascular function. These events regulate complex processes such as gonadotropin pulsatility, ovulation, implantation and parturition. During reproductive life, a number of neuropeptides produced within the hypothalamus play a modulatory role in the control of gonadotropin-releasing hormone (GnRH) release, hence characterizing a hypothalamic paracrine system. The pituitary gland is a source and target of inhibin-related proteins, and these typical 'gonadal' products, once secreted by the pituitary cells, acquire the function of paracrine modulators of follicle-stimulating hormone (FSH) secretion. In the ovary, the effect of gonadotropins is locally modulated by growth factors acting in an autocrine/paracrine manner, although their precise role in folliculogenesis remains uncertain. Numerous local factors are involved in the control of endometrial growth, differentiation, receptivity and menstruation. Alterations in the paracrine endometrial system may underlie pathological processes such as infertility or endometrial neoplasia. The human placenta and its related membranes produce cytokines, hormones and growth factors that participate in the control of gestational development as well as in the maternal-fetal adaptation to gestational diseases. There is increasing evidence that paracrine signaling plays a fundamental role in all spheres of female reproductive function, and future research will concentrate on clarifying which of these local mechanisms play a decisive role in both physiology and disease, thus giving rise to new therapeutic strategies.

Prolactin: structure, function, and regulation of secretion

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

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)

Hormonal and developmental regulation of pulmonary surfactant synthesis in fetal lung

Pulmonary surfactant, a unique developmentally regulated, phospholipid-rich lipoprotein, is synthesized by the type II cells of the pulmonary alveolus, where it is stored in organelles termed lamellar bodies. The principal surface-active component of surfactant, dipalmitoylphosphatidylcholine, a disaturated form of phosphatidylcholine, acts in concert with the surfactant-associated proteins to reduce alveolar surface tension. Relatively large amounts of phosphatidylglycerol also are present in lung surfactants of a number of species, including man. The role of phosphatidylglycerol in surfactant function has not been elucidated; however, its presence in increased amounts in pulmonary surfactant is correlated with enhanced fetal lung maturity. Surfactant glycerophospholipid synthesis in fetal lung tissue is regulated by a number of hormones and factors, including glucocorticoids, prolactin, insulin, oestrogens, androgens, thyroid hormones, and catecholamines acting through cyclic AMP. In studies with human fetal lung in organ culture, we have observed that glucocorticoids, in combination with prolactin and/or insulin, increase the rate of lamellar body phosphatidylcholine synthesis and alter lamellar body glycerophospholipid composition to one reflective of surfactant secreted by the human fetal lung at term. Four surfactant-associated proteins, SP-A, SP-B, SP-C and SP-D, have recently been characterized. Recognition of their potential importance in the reduction of alveolar surface tension and in endocytosis and reutilization of secreted surfactant by type II cells has stimulated rapid advancement of knowledge concerning the structures of the surfactant proteins and their genes, as well as their developmental and hormonal regulation in fetal lung tissue. The genes encoding SP-A, SP-B and SP-C are expressed in a cell-specific manner and are independently regulated in fetal lung tissue during development. SP-A gene expression occurs exclusively in the type II cell and is initiated after 75% of gestation is complete. In the human fetus, expression of the SP-B and SP-C genes is detectable much earlier in development than SP-A, before the time of appearance of differentiated type II cells. It is apparent from studies using human and rabbit fetal lung in culture that cyclic AMP and glucocorticoids serve important roles in the regulation of SP-A gene expression. While the effects of cyclic AMP are exerted primarily at the level of gene transcription in human fetal lung tissue, glucocorticoids have stimulatory effects on SP-A gene transcription and inhibitory effects on SP-A mRNA stability. In addition, cyclic AMP and glucocorticoids act synergistically to increase SP-A gene transcription in human fetal lung in vitro.(ABSTRACT TRUNCATED AT 400 WORDS)

Amniotic fluid prolactin levels in rhesus isoimmunized patients

The concentration of prolactin in the amniotic fluid (AFPRL) was measured in 75 samples obtained in the third trimester of 14 isoimmunized women. There was a uniform decline in prolactin levels with advancing gestation in each pregnancy (r = -0.89 to -0.99). The decline in AFPRL was similar in uncomplicated pregnancies. AFPRL levels were not predictive of umbilical cord hemoglobin or bilirubin levels and amniotic fluid lecithin/sphingomyelin ratio.

Role of placental lactogen and prolactin in human pregnancy

In summary, studies from our and other laboratories strongly suggest that placental lactogen has direct effects on fetal growth and metabolism as well as on maternal metabolism. Prolactin may be important in the regulation of water and ion transport across the amnion, the production of surfactant by the fetal lung, and the immune response during pregnancy. A summary of the postulated effects of placental lactogen on maternal and fetal physiology is depicted in Figure 9 and a summary of the postulated effects of prolactin during pregnancy is shown in Table 6. Undoubtedly, future studies of the physiology of placental lactogen and prolactin will uncover new functions for these hormones during gestation.