Defective mammopoiesis, but normal hematopoiesis, in mice with a targeted disruption of the prolactin gene

Prolactin (PRL) has been implicated in numerous physiological and developmental processes. The mouse PRL gene was disrupted by homologous recombination. The mutation caused infertility in female mice, but did not prevent female mice from manifesting spontaneous maternal behaviors. PRL-deficient males were fertile and produced offspring with normal Mendelian gender and genotype ratios when they were mated with heterozygous females. Mammary glands of mutant female mice developed a normal ductal tree, but the ducts failed to develop lobular decorations, which is a characteristic of the normal virgin adult mammary gland. The potential effect of PRL gene disruption on antigen-independent primary hematopoiesis was assessed. The results of this analysis indicated that myelopoiesis and primary lymphopoiesis were unaltered in the mutant mice. Consistent with these observations in PRL mutant mice, PRL failed to correct the bone marrow B cell deficiency of Snell dwarf mice. These results argue that PRL does not play any indispensable role in primary lymphocyte development and homeostasis, or in myeloid differentiation. The PRL-/- mouse model provides a new research tool with which to resolve a variety of questions regarding the involvement of both endocrine and paracrine sources of PRL in reproduction, lactogenesis, tumorigenesis and immunoregulation.

Mutations in PROP1 cause familial combined pituitary hormone deficiency

Combined pituitary hormone deficiency (CPHD) in man denotes impaired production of growth hormone (GH) and one or more of the other five anterior pituitary hormones. Mutations of the pituitary transcription factor gene POU1F1 (the human homologue of mouse Pit1) are responsible for deficiencies of GH, prolactin and thyroid stimulating hormone (TSH) in Snell and Jackson dwarf mice and in man, while the production of adrenocorticotrophic hormone (ACTH), luteinizing hormone (LH) and follicle stimulating hormone (FSH) is preserved. The Ames dwarf (df) mouse displays a similar phenotype, and appears to be epistatic to Snell and Jackson dwarfism. We have recently positionally cloned the putative Ames dwarf gene Prop1, which encodes a paired-like homeodomain protein that is expressed specifically in embryonic pituitary and is necessary for Pit1 expression. In this report, we have identified four CPHD families with homozygosity or compound heterozygosity for inactivating mutations of PROP1. These mutations in the human PROP1 gene result in a gene product with reduced DNA-binding and transcriptional activation ability in comparison to the product of the murine df mutation. In contrast to individuals with POU1F1 mutations, those with PROP1 mutations cannot produce LH and FSH at a sufficient level and do not enter puberty spontaneously. Our results identify a major cause of CPHD in humans and suggest a direct or indirect role for PROP1 in the ontogenesis of pituitary gonadotropes, as well as somatotropes, lactotropes and caudomedial thyrotropes.

Mutation of the POU-specific domain of Pit-1 and hypopituitarism without pituitary hypoplasia

A point mutation in the POU-specific portion of the human gene that encodes the tissue-specific POU-domain transcription factor, Pit-1, results in hypopituitarism, with deficiencies of growth hormone, prolactin, and thyroid-stimulating hormone. In two unrelated Dutch families, a mutation in Pit-1 that altered an alanine in the first putative alpha helix of the POU-specific domain to proline was observed. This mutation generated a protein capable of binding to DNA response elements but unable to effectively activate its known target genes, growth hormone and prolactin. The phenotype of the affected individuals suggests that the mutant Pit-1 protein is competent to initiate other programs of gene activation required for normal proliferation of somatotrope, lactotrope, and thyrotrope cell types. Thus, a mutation in the POU-specific domain of Pit-1 has a selective effect on a subset of Pit-1 target genes.

A mutation in the POU-homeodomain of Pit-1 responsible for combined pituitary hormone deficiency

Pit-1 is a pituitary-specific transcription factor responsible for pituitary development and hormone expression in mammals. Mutations in the gene encoding Pit-1 have been found in two dwarf mouse strains displaying hypoplasia of growth hormone, prolactin, and thyroid-stimulating, hormone-secreting cell types in the anterior pituitary. A point mutation in this gene was identified on one allele in a patient with combined pituitary hormone deficiency. Mutant Pit-1 binds DNA normally but acts as a dominant inhibitor of Pit-1 action in the pituitary.

Life extension in the dwarf mouse

Ames dwarf mice and Snell dwarf mice lack growth hormone (GH), prolactin (PRL), and thyroid-stimulating hormone (TSH), live much longer than their normal siblings, and exhibit many symptoms of delayed aging. "Laron dwarf mice," produced by targeted disruption of the GH receptor/GH-binding protein gene (GHR-KO mice), are GH resistant and also live much longer than normal animals from the same line. Isolated GH deficiency in "little" mice is similarly associated with increased life span, provided that obesity is prevented by reducing fat content in the diet. Long-lived dwarf mice share many phenotypic characteristics with genetically normal (wild-type) animals subjected to prolonged caloric restriction (CR) but are not CR mimetics. We propose that mechanisms linking GH deficiency and GH resistance with delayed aging include reduced hepatic synthesis of insulin-like growth factor 1 (IGF-1), reduced secretion of insulin, increased hepatic sensitivity to insulin actions, reduced plasma glucose, reduced generation of reactive oxygen species, improved antioxidant defenses, increased resistance to oxidative stress, and reduced oxidative damage. The possible role of hypothyroidism, reduced body temperature, reduced adult body size, delayed puberty, and reduced fecundity in producing the long-lived phenotype of dwarf mice remains to be evaluated. An important role of IGF-1 and insulin in the control of mammalian longevity is consistent with the well-documented actions of homologous signaling pathways in invertebrates.

Cretinism with combined hormone deficiency caused by a mutation in the PIT1 gene

Cretinism is marked by irreversible mental and growth retardation. We describe here an entirely new case of cretinism showing combined pituitary hormone deficiencies of thyrotropin, growth hormone and prolactin that appears to be caused by homozygosity for a nonsense mutation in the gene for the pituitary specific transcription activator, Pit-1/GHF-1 (designated PIT1 in humans for pituitary specific factor 1). This is the first report in humans of a defect in a transcription activator causing deficiency of multiple target genes.

Serotonin Regulates Mammary Gland Development via an Autocrine-Paracrine Loop

Mammary gland development is controlled by a dynamic interplay between endocrine hormones and locally produced factors. Biogenic monoamines (serotonin, dopamine, norepinephrine, and others) are an important class of bioregulatory molecules that have not been shown to participate in mammary development. Here we show that mammary glands stimulated by prolactin (PRL) express genes essential for serotonin biosynthesis (tryptophan hydroxylase [TPH] and aromatic amine decarboxylase). TPH mRNA was elevated during pregnancy and lactation, and serotonin was detected in the mammary epithelium and in milk. TPH was induced by PRL in mammosphere cultures and by milk stasis in nursing dams, suggesting that the gene is controlled by milk filling in the alveoli. Serotonin suppressed beta-casein gene expression and caused shrinkage of mammary alveoli. Conversely, TPH1 gene disruption or antiserotonergic drugs resulted in enhanced secretory features and alveolar dilation. Thus, autocrine-paracrine serotonin signaling is an important regulator of mammary homeostasis and early involution.

Prolonged lymphopenia, lymphoid depletion, and hypoprolactinemia in children with nosocomial sepsis and multiple organ failure

Lymphopenia and lymphoid depletion occur in adults dying of sepsis. Prolactin increases Bcl-2 expression, suppresses stress-induced lymphocyte apoptosis, and improves survival from experimental sepsis. We hypothesized that prolonged lymphopenia, lymphoid depletion, and hypoprolactinemia occur in children dying with sepsis and multiple organ failure (MOF). Fifty-eight critically ill children with and 55 without MOF admitted to a university hospital pediatric intensive care unit were enrolled in a prospective, longitudinal, observational clinical study. Prolactin levels and absolute lymphocyte count were measured on days 1, 3, 7, 14, and 21. Lymph node, thymus, and spleen autopsy specimens were examined for lymphoid depletion, with immunohistochemical staining for CD4, CD20, and CD21 and for lymphoid apoptosis. Prolonged lymphopenia (absolute lymphocyte count < 1000 for >7 days) occurred only in children with MOF (29 vs 0%, p < 0.05) and was associated independently with nosocomial infection (odds ratio (OR), 5.5, 95% confidence interval (CI), 1.7-17, p < 0.05), death (OR, 6.8, 95% CI, 1.3-34, p < 0.05), and splenic and lymph node hypocellularity (OR, 42, 95% CI, 3.7-473, p < 0.05). Lymphocyte apoptosis and ante/postmortem infection were observed only in children with lymphoid depletion. Prolonged hypoprolactinemia (>7 days) was more common in children with MOF (17 vs 2%, p < 0.05) and was associated independently with prolonged lymphopenia (OR, 8.3, 95% CI, 2.1-33, p < 0.05) and lymphoid depletion (OR, 12.2, 95% CI, 2.2-65, p < 0.05). Prolonged lymphopenia and apoptosis-associated depletion of lymphoid organs play a role in nosocomial sepsis-related death in critically ill children. Prolonged hypoprolactinemia is a previously unrecognized risk factor for this syndrome.

Hypopituitarism

Hypopituitarism refers to deficiency of one or more hormones produced by the anterior pituitary or released from the posterior pituitary. Hypopituitarism is associated with excess mortality, a key risk factor being cortisol deficiency due to adrenocorticotropic hormone (ACTH) deficiency. Onset can be acute or insidious, and the most common cause in adulthood is a pituitary adenoma, or treatment with pituitary surgery or radiotherapy. Hypopituitarism is diagnosed based on baseline blood sampling for thyroid stimulating hormone, gonadotropin, and prolactin deficiencies, whereas for ACTH, growth hormone, and antidiuretic hormone deficiency dynamic stimulation tests are usually needed. Repeated pituitary function assessment at regular intervals is needed for diagnosis of the predictable but slowly evolving forms of hypopituitarism. Replacement treatment exists in the form of thyroxine, hydrocortisone, sex steroids, growth hormone, and desmopressin. If onset is acute, cortisol deficiency should be replaced first. Modifications in replacement treatment are needed during the transition from paediatric to adult endocrine care, and during pregnancy.

Prolactin - a pleiotropic factor in health and disease

The principal role of prolactin in mammals is the regulation of lactation. Prolactin is a hormone that is mainly synthesized and secreted by lactotroph cells in the anterior pituitary gland. Prolactin signalling occurs via a unique transmembrane prolactin receptor (PRL-R). The structure of the PRL-R has now been elucidated and is similar to that of many biologically fundamental receptors of the class 1 haematopoietic cytokine receptor family such as the growth hormone receptor. The PRL-R is expressed in a wide array of tissues, and a growing number of biological processes continue to be attributed to prolactin. In this Review, we focus on the newly discovered roles of prolactin in human health and disease, particularly its involvement in metabolic homeostasis including body weight control, adipose tissue, skin and hair follicles, pancreas, bone, the adrenal response to stress, the control of lactotroph cell homeostasis and maternal behaviour. New data concerning the pathological states of hypoprolactinaemia and hyperprolactinaemia will also be presented and discussed.

Increased insulin sensitivity and upregulation of insulin receptor, insulin receptor substrate (IRS)-1 and IRS-2 in liver of Ames dwarf mice

In the present study we have used hypopituitary Ames dwarf mice, which lack GH, prolactin and TSH, to investigate the consequences of the deficiency of these hormones on glucose homeostasis and on the initial components of the insulin signal transduction pathway in the liver. Ames dwarf mice displayed hypersensitivity to insulin since they maintained lower fasting glucose concentrations (73% of control values), had significantly reduced amounts of insulin (58% of control values), and exhibited an increased hypoglycemic response to exogenous insulin. Probably as a result of reduced insulin production, Ames dwarf mice displayed intolerance to glucose. The insulin-stimulated phosphorylation of the insulin receptor (IR) tended to be increased in the liver of Ames dwarf mice, while IR receptor protein content was increased by 38%. Insulin-stimulated phosphorylation of insulin receptor substrate (IRS)-1 and IRS-2 was increased by 61 and 72% respectively, while IRS-1 and IRS-2 protein levels were increased by 76 and 95%. The insulin-stimulated association of the p85 regulatory subunit of phosphatidylinositol (PI) 3-kinase with IRS-1 was increased by 28%, but unaltered with IRS-2. Interestingly, while the insulin-stimulated phosphotyrosine-derived PI 3-kinase activity was not changed, insulin-stimulated protein kinase B activation was increased by 41% in this tissue. These alterations may account for the insulin hypersensitivity exhibited by these animals. The present findings in long-lived Ames dwarf mice add to the evidence that insulin signaling is importantly related to the regulation of aging and life span.

Lymphocytic and granulomatous hypophysitis: experience with nine cases

OBJECTIVE

Lymphocytic hypophysitis and granulomatous hypophysitis are rarely encountered. The aim of this study was to demonstrate their clinical peculiarities among pituitary disorders and to provide an approach for their clinical management.

METHODS

In a retrospective study, we reviewed our surgical experience with nine patients harboring hypophysitis. The series included six cases of lymphocytic hypophysitis, two cases of granulomatous hypophysitis, and one case with evidence of coexisting lymphocytic and granulomatous hypophysitis.

RESULTS

A striking similarity of clinical signs was found for our nine patients. Headache or aseptic meningitis, thickening of the sphenoid sinus mucosa, pituitary stalk enlargement, and tongue-shaped extension of the lesion along the basal hypothalamus were characteristic signs. Lymphocytic hypophysitis was not associated with pregnancy in any of the seven cases. No recurrence has been observed in six cases with total removal of the inflammatory tissue.

CONCLUSION

Lymphocytic hypophysitis and granulomatous hypophysitis represent related inflammatory disorders. Their conspicuous clinical features frequently allow preoperative diagnosis of hypophysitis. In view of their sometimes insidious clinical course, early surgical exploration is justified.

Endocrine deficit after fractionated total body irradiation

Endocrine function was assessed in 31 children (17 boys) after fractionated total body irradiation used in the preparative regimen for bone marrow transplantation. Endocrine dysfunction was present in 25 children. Fifteen of 29 had growth hormone insufficiency 0.9-4.9 years after total body irradiation, yet only three of the 15 had received previous cranial irradiation. Five of 30 had thyroid dysfunction: two with a low thyroxine and raised thyroid stimulating hormone (TSH) concentration and three with a raised TSH and normal thyroxine concentration. Thus the incidence of thyroid dysfunction (16%) is much lower than that reported after single fraction total body irradiation (39-59%). In only two children were abnormalities of the hypothalamic-pituitary-adrenal axis demonstrated. The majority of pubertal children assessed (n = 15) showed evidence of gonadal damage. All the pubertal girls (n = 5) had ovarian failure, although there was evidence of recovery of ovarian function in one girl. All seven boys in late puberty showed evidence of damage to the germinal epithelium, and two of three in early puberty had raised follicle stimulating hormone concentrations. Despite the use of a fractionated total body irradiation regimen, endocrine morbidity is substantial and children undergoing such procedures will require long term endocrine review and management.

Hypopituitarism following Radiotherapy Revisited

Neuroendocrine disturbances in anterior pituitary hormone secretion are common following radiation damage to the hypothalamic-pituitary (H-P) axis, the severity and frequency of which correlate with the total radiation dose delivered to the H-P axis and the length of follow-up. The somatotropic axis is the most vulnerable to radiation damage and GH deficiency remains the most frequently seen endocrinopathy. Compensatory hyperstimulation of a partially damaged somatotropic axis may restore normality of spontaneous GH secretion in the context of reduced but normal stimulated responses in adults. At its extreme, endogenous hyperstimulation may limit further stimulation by insulin-induced hypoglycaemia resulting in subnormal GH responses despite the normality of spontaneous GH secretion. In children, failure of the hyper-stimulated partially damaged H-P axis to meet the increased demands for GH during growth and puberty may explain what has previously been described as radiation-induced GH neurosecretory dysfunction and, unlike in adults, the insulin tolerance test remains the gold standard for assessing H-P functional reserve. With low radiation doses (<30 Gy) GH deficiency usually occurs in isolation in about 30% of patients, while with radiation doses of 30-50 Gy, the incidence of GH deficiency can reach 50-100% and long-term gonadotropin, TSH and ACTH deficiencies occur in 20-30, 3-9 and 3-6% of patients, respectively. With higher dose cranial irradiation (>60 Gy) or following conventional irradiation for pituitary tumours (30-50 Gy), multiple hormonal deficiencies occur in 30-60% after 10 years of follow-up. Precocious puberty can occur after radiation doses of <30 Gy in girls only, and in both sexes equally with a radiation dose of 30-50 Gy. Hyperprolactinaemia, due to hypothalamic damage is mostly seen in young women after high dose cranial irradiation and is usually subclinical. H-P dysfunction is progressive and irreversible and can have an adverse impact on growth, body image, sexual function and quality of life. Regular testing is advised to ensure timely diagnosis and early hormone replacement therapy.

Stimulation of growth in the little mouse

The new mouse mutation little (lit) in the homozygous state causes a pituitary deficiency involving at least growth hormone (GH) and prolactin. The resultant growth failure of lit/lit mice was shown to be reversed by experimental conditions that enhanced levels of GH or GH and prolactin in the circulation. Two measures of growth, actual weight gain and bone dimension, were significantly improved by the physiological processes of pregnancy and pseudopregnancy, by extra-sellar graft of a normal mouse pituitary, and by treatment with GH but not prolactin. These data confirmed pituitary dysfunction as the basic defect caused by the mutation lit and showed that the GH deficiency is responsible for growth failure. However, the biological site of gene action, the pituitary or hypothalamus, has not been established. Little mice exhibit a number of characteristics similar to those of human genetic ateleotic dwarfism Type 1, namely genetic inheritance, time of onset of growth retardation, proportionate skeletal size reduction, and pituitary GH deficiency.

Growth hormone and insulin-like growth factor I treatment increase testicular luteinizing hormone receptors and steroidogenic responsiveness of growth hormone deficient dwarf mice

To test the hypothesis that insulin-like growth factor (IGF-I) is required for the in vivo development of testicular Leydig cell function, either recombinant human GH [(hGH) (1.5 micrograms/g BW) or recombinant IGF-I (1 microgram/g BW) was injected three times daily into immature Snell dwarf mice (dw/dw) and into phenotypically normal control (Dw/-) for 7 days. In dw/dw mice hGH enhanced significantly body, liver, kidney, and testicular weight. In addition, hGH increased testicular LH receptors and the acute steroidogenic response to human CG, but there was no significant effect on basal plasma testosterone or plasma LH levels. The effects of IGF-I in body and kidney weight were less pronounced than those produced by hGH, but its effects on testicular weight and LH receptors, as well as on the acute steroidogenic response to human CG, were similar to that observed after hGH treatment. In Dw/- mice hGH had no effect on either body or organ weight or on testicular function, despite the fact that it induced a significant increase in plasma IGF-I levels. These results indicated that IGF-I is able to induce the maturation of Leydig cell function and that the effects of hGH on the testis are probably mediated by IGF-I. They also suggest that the delayed puberty associated with GH deficiency or resistance is most likely related to an IGF-I deficiency.

Hypopituitarism

Hypopituitarism is the partial or complete insufficiency of anterior pituitary hormone secretion and may result from pituitary or hypothalamic disease. The reported incidence (12-42 new cases per million per year) and prevalence (300-455 per million) is probably underestimated if its occurrence after brain injuries (30-70% of cases) is considered. Clinical manifestations depend on the extent of hormone deficiency and may be non specific, such as fatigue, hypotension, cold intolerance, or more indicative such as growth retardation or impotence and infertility in GH and gonadotropin deficiency, respectively.A number of inflammatory, granulomatous or neoplastic diseases as well as traumatic or radiation injuries involving the hypothalamic-pituitary region can lead to hypopituitarism. Several genetic defects are possible causes of syndromic and non syndromic isolated/multiple pituitary hormone deficiencies. Unexplained gonadal dysfunctions, developmental craniofacial abnormalities, newly discovered empty sella and previous pregnancy-associated hemorrhage or blood pressure changes may be associated with defective anterior pituitary function.The diagnosis of hypopituitarism relies on the measurement of basal and stimulated secretion of anterior pituitary hormones and of the hormones secreted by pituitary target glands. MR imaging of the hypothalamo-pituitary region may provide essential information. Genetic testing, when indicated, may be diagnostic.Secondary hypothyroidism is a rare disease. The biochemical diagnosis is suggested by low serum FT4 levels and inappropriately normal or low basal TSH levels that do not rise normally after TRH. L-thyroxine is the treatment of choice. Before starting replacement therapy, concomitant corticotropin deficiency should be excluded in order to avoid acute adrenal insufficiency. Prolactin deficiency is also very rare and generally occurs after global failure of pituitary function. Prolactin deficiency prevents lactation. Hypogonadotropic hypogonadism in males is characterized by low testosterone with low or normal LH and FSH serum concentrations and impaired spermatogenesis. Hyperprolactinemia as well as low sex hormone binding globulin concentrations enter the differential diagnosis. Irregular menses and amenorrhea with low serum estradiol concentration (<100 pmol/l) and normal or low gonadotropin concentrations are the typical features of hypogonadotropic hypogonadism in females. In post menopausal women, failure to detect high serum gonadotropin values is highly suggestive of the diagnosis. In males, replacement therapy with oral or injectable testosterone results in wide fluctuations of serum hormone levels. More recently developed transdermal testosterone preparations allow stable physiological serum testosterone levels. Pulsatile GnRH administration can be used to stimulate spermatogenesis in men and ovulation in women with GnRH deficiency and normal gonadotropin secretion. Gonadotropin administration is indicated in cases of gonadotropin deficiency or GnRH resistance but is also an option, in alternative to pulsatile GnRH, for patients with defective GnRH secretion.

Prolactin deficiency in pseudohypoparathyroidism

Because thyrotropin deficiency may occur in pseudohypoparathyroidism, we studied pituitary function in two families with this condition. Six of eight patients had impaired pituitary prolactin secretion after administration of thyrotropin-releasing hormone and chlorpromazine, with preservation of other anterior pituitary functions. Peak serum prolactin levels after thyrotropin-releasing hormone and chlorpromazine in the prolactin-deficient patients were significantly lower than normal. Administration of diethylstilbestrol for five days, which normally enhances prolactin responses to thyrotropin-releasing hormone, had no effect on prolactin secretion in these patients. Although antilactotroph antibodies were not demonstrable, hypothyroidism or decreased thyroid reserve in four and antithyroid and antiparietal-cell antibodies in several family members suggest that an associated autoimmune process may be responsible for the prolactin deficiency.

Characteristic features of 20 patients with Sheehan's syndrome

Sheehan's syndrome occurs as a result of ischemic pituitary necrosis due to severe postpartum hemorrhage. The aim of the present study was to determine the clinical characteristics of Sheehan's syndrome in 20 patients (mean age 60.15 +/- 3.41 years) with typical obstetric history. The mean duration between time of diagnosis and date of the last delivery was 26.82 +/- 2.52 years (range 2-40 years). All patients had a history of massive hemorrhage at delivery and physical signs of Sheehan's syndrome. Fourteen patients (70.0%) lacked postpartum milk production and did not menstruate following delivery. Baseline and stimulated anterior pituitary hormone levels were measured in all patients. According to the hormonal values, 18 (90.0%) patients had secondary hypothyroidism, 11 (55.0%) had adrenal failure and all of them had hypogonadism, prolactin and growth hormone deficiency. Hyponatremia was present in seven patients (35.0%). Total or partially empty sella was revealed in all patients by magnetic resonance imaging. Diabetes insipidus was not found in any patient. We found that lack of lactation in the postpartum period and early menopause seemed the most important clues for diagnosis of Sheehan's syndrome, and inadequate prolactin and gonadotropin responses to stimulation tests were the most sensitive diagnostic signs in patients with severe postpartum hemorrhage.

Body composition of prolactin-, growth hormone, and thyrotropin-deficient Ames dwarf mice

Ames dwarf mice have primary deficiency of prolactin (PRL), growth hormone (GH), and thyroid-stimulating hormone (TSH), and live considerably longer than normal animals from the same line. In view of the documented effects of GH, PRL, and thyroid hormones on lean and fat body mass and skeletal growth, and the suspected relationship of body size and composition to life expectancy, it was of interest to examine age-related changes in body composition of Ames dwarf mice. Lean mass, fat mass, bone area, and bone mineral content (BMC) were determined in dwarf and normal mice at the ages of 2, 4.5 6, and 18 mo using dual X-ray absorptiometry. In addition to the expected significant declines in lean mass, bone area, and BMC, dwarf mice exhibited attenuation of the age-related increase in bone mineral density and delayed or attenuated increase in percentage of body fat. Percentage of body fat was lower in adult dwarfs than in the corresponding normal controls. Patterns of age-related changes in body composition in Ames dwarf mice are consistent with the recent report of age-related changes in body composition in PRL receptor knockout mice. We suspect that reduction in relative adiposity may contribute to the previously reported increase in insulin sensitivity of Ames dwarf mice and thus may be a factor in delayed aging and increased longevity of these animals.

Induction of prolactin-deficient variants of GH3 rat pituitary tumor cells by ethyl methanesulfonate: reversion by 5-azacytidine, a DNA methylation inhibitor

GH3 cells are a rat pituitary tumor line expressing two pituitary peptide hormones, prolactin (rPRL) and growth hormone. Recently, it was found that the DNA alkylating agent ethyl methanesulfonate can induce the appearance of rPRL-deficient GH3 cell variants at a high frequency (ca. 20-30%). As shown here, such variants cannot be induced at high frequency by irradiation of wild-type GH3 cells with ultraviolet light, indicating that the effect may be specific to treatment with alkylating agents. Furthermore, the DNA methylation inhibitor 5-azacytidine reverted an ethyl methanesulfonate-induced rPRL-deficient variant into rPRL-expressing cells at high frequency (ca. 50%). The revertants were stable for at least 30-35 generations. These results support the hypothesis that the alkylating agent may promote the specific methylation of the rPRL gene or a gene regulating its activity, either one of which leads to inactivation of expression of the rPRL gene in GH3 cells.

Humoral and cell-mediated immunity in mice with genetic deficiencies of prolactin, growth hormone, insulin-like growth factor-I, and thyroid hormone

Prolactin (PRL), growth hormone (GH), insulin-like growth factor-I (IGF-I), and thyroid hormones have been proposed as critical immunoregulatory mediators, and their clinical use is being considered. The precise role played by each of these hormones in the generation of humoral and cell-mediated immune responses was assessed in a panel of mice with mutations that result in a selective reduction of PRL, GH, IGF-I, and/or thyroid hormone production. A surprising result, in view of previous studies indicating an immunoregulatory role for these hormones, was that all mice generated normal humoral and cell-mediated immune responses following challenge with T-independent and T-dependent antigens and with Listeria monocytogenes. A review of these findings in the context of previous data has resulted in the formulation of a working hypothesis proposing that these hormones act as anabolic and/or stress modulating mediators with effects on most cells, including those of the immune system. When considered in this context, it is possible to reconcile the contradictory data.

A uterine decidual cell cytokine ensures pregnancy-dependent adaptations to a physiological stressor

In the mouse, decidual cells differentiate from uterine stromal cells in response to steroid hormones and signals arising from the embryo. Decidual cells are crucially involved in creating the intrauterine environment conducive to embryonic development. Among their many functions is the production of cytokines related to prolactin (PRL), including decidual prolactin-related protein (DPRP). DPRP is a heparin-binding cytokine, which is abundantly expressed in uterine decidua. In this investigation, we have isolated the mouse Dprp gene, characterized its structure and evaluated its biological role. Dprp-null mice were made by replacing exons 2 to 6 of the Dprp gene with an in-frame enhanced green fluorescent protein (EGFP) gene and a neomycin (neo) resistance cassette. Heterozygous intercross breeding of the mutant mice yielded the expected mendelian ratio. Pregnant heterozygote females expressed EGFP within decidual tissue in locations identical to endogenous Dprp mRNA and protein expression. Homozygous Dprp-null mutant male and female mice were viable, exhibited normal postnatal growth rates, were fertile and produced normal litter sizes. A prominent phenotype was observed when pregnant Dprp-null mice were exposed to a physiological stressor. DPRP deficiency interfered with pregnancy-dependent adaptations to hypoxia resulting in pregnancy failure. Termination of pregnancy was associated with aberrations in mesometrial decidual cells, mesometrial vascular integrity, and disruptions in chorioallantoic placenta morphogenesis. The observations suggest that DPRP participates in pregnancy-dependent adaptations to a physiological stressor.