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Follicle-stimulating hormone (Fsh) is a major regulator of spermatogenesis, targeting somatic cell functions in the testes. We reported previously that zebrafish Fsh promoted the differentiation of type A undifferentiated spermatogonia (A und ) by stimulating the production of factors that advance germ cell differentiation, such as androgens, insulin-like peptide 3 (Insl3) and insulin-like growth factor 3 (Igf3). In addition, Fsh also modulated the transcript levels of several other genes, including some belonging to the Wnt signaling pathway. Here, we evaluated if and how Fsh utilizes part of the canonical Wnt pathway to regulate the development of spermatogonia. We quantified the proliferation activity and relative section areas occupied by A und and type A differentiating (A diff ) spermatogonia and we analyzed the expression of selected genes in response to recombinant proteins and pharmacological inhibitors. We found that from the three downstream mediators of Fsh activity we examined, Igf3, but not 11-ketotestosterone or Insl3, modulated the transcript levels of two β-catenin sensitive genes ( cyclinD1 and axin2 ). Using a zebrafish β-catenin signaling reporter line, we showed that Igf3 activated β-catenin signaling in type A spermatogonia and that this activation did not depend on the release of Wnt ligands. Pharmacological inhibition of the β-catenin or of the phosphoinositide 3-kinase (PI3K) pathways revealed that Igf3 activated β-catenin signaling in a manner involving PI3K to promote the differentiation of A und to A diff spermatogonia. This mechanism represents an intriguing example for a pituitary hormone like Fsh using Igf signaling to recruit the evolutionary conserved, local β-catenin signaling pathway to regulate spermatogenesis., (© 2018 Society for Endocrinology.)

For many decades, elevated androgens in women have been associated with poor reproductive health. However, recent studies have shown that androgens play a crucial role in women's fertility. The following review provides an overall perspective about how androgens and androgen receptor-mediated actions regulate normal follicular development, as well as discuss emerging concepts, latest perceptions, and controversies regarding androgen actions and signaling in the ovary., (© 2014 Society for Endocrinology.)

Normal development and function of the placenta is critical to achieving a successful pregnancy, as normal fetal growth depends directly on the transfer of nutrients from mother to fetus via this organ. Recently, it has become apparent from both animal and human studies that growth factors within the maternal circulation, for example the IGFs, are important regulators of placental development and function. Although these factors act via distinct receptors to exert their effects, the downstream molecules activated upon ligand/receptor interaction are common to many growth factors. The expression of numerous signaling molecules is altered in the placentas from pregnancies affected by the fetal growth complications, fetal growth restriction, and macrosomia. Thus, targeting these molecules may lead to more effective treatments for complications of pregnancy associated with altered placental development. Here, we review the maternal growth factors required for placental development and discuss their mechanism of action.

The insulin-like growth factors-I and -II (IGFs) are involved in a wide array of cellular processes such as proliferation, prevention of apoptosis, and differentiation. Most of these effects are mediated by the IGF-I receptor, although at higher IGF concentrations the insulin receptor can also be activated. As the expression of both the IGFs and their receptors is widespread, IGFs are thought to have autocrine/paracrine modes of actions also, particularly during foetal life. The endocrine component of the IGF system is recognised to be important after birth, with IGF-I mediating many of the effects of growth hormone (GH), and linking anabolic processes to nutrient availability. Consideration of ligands and receptors, however, is insufficient to provide a complete understanding of the biology of IGF. This is because IGFs are found in binary complexes of 40-50 kDa with members of a family of IGF-binding proteins (IGFBPs-1 to -6) in all biological fluids. In addition, in postnatal serum, most IGFs are sequestered into ternary complexes of 150 kDa consisting of one molecule each of IGF, IGFBP-3 or IGFBP-5, and acid-labile subunit (ALS). Despite evidence that ALS plays an important role in the biology of circulating IGFs, it has received only limited attention relative to the other components of the IGF system. This review provides an overview on the current knowledge of ALS protein and gene structure, organisation and regulation by hormones, and insights from novel animal models such as the ALS knockout mice.

By combining data from studies of multinodular non-toxic goitre (MNTG) with data from rat models of goitre induction and in vitro models, a map of the growth factors involved in goitrogenesis has been constructed. We have addressed the roles of the insulin-like growth factors, transforming growth factors, fibroblast growth factors, endothelins, etc. We hypothesise that an imbalance in the interactions between the various growth factor axes exists in MNTG which favours cell replication. Thyrotrophin, although not significantly elevated in MNTG, exerts critical effects through interactions with autocrine and paracrine factors and their receptors. Expansion of the thyroidal vascular bed through angiogenesis is closely co-ordinated with follicular cell expansion and folliculoneogenesis, and while the integrated paracrine actions of fibroblast growth factors, vascular endothelial growth factor and endothelin probably play central roles, additional, as yet elusive, factors are probably involved. The combination of in vitro and in vivo approaches, designed to address specific questions, will undoubtedly continue to prove invaluable in dissecting further the complex interactions that exist between these growth factors, their binding proteins and receptors in goitrogenesis.

Inhibition of prolactin secretion with bromocriptine and neutralization of GH action with a specific antiserum to rat GH (rGH) were used to explore the modes of action of GH and prolactin in maintaining lactation in the rat. Treatment of dams with anti-rGH caused a small reduction in litter weight gain whilst bromocriptine reduced litter weight gain by 50%. When both treatments were combined, however, milk yield ceased completely and this was accompanied by a wide variety of effects on mammary lipid metabolism including decreases in the mRNA concentrations of acetyl CoA carboxylase, fatty acid synthase, malic enzyme and lipoprotein lipase. Activities of acetyl CoA carboxylase and lipoprotein lipase were also significantly reduced. Reciprocal changes were evident in adipose tissue with increases in acetyl CoA carboxylase and lipoprotein lipase activities. In conjunction with a decreased lipolytic response to noradrenaline in adipose tissue of animals given the combined treatment of bromocriptine and anti-rGH, this represented a co-ordinated series of changes to reduce lipid synthesis in the mammary gland and enhance lipogenesis and triglyceride storage in adipose tissue as milk production ceased. All of these effects could be prevented in part by concurrent treatment with GH, but insulin-like growth factor-I (IGF-I) and IGF-II failed to affect any of the parameters measured.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of GH was examined using an antiserum to rat GH (anti-rGH). When administered to lactating rats on day 2 of lactation it was without effect, whereas bromocriptine markedly suppressed milk production, with no additional effect of combined treatment. On day 6 of lactation, treatment with anti-rGH was also without effect, whilst bromocriptine again suppressed milk production. Combined treatment, however, suppressed milk synthesis completely, suggesting that GH was capable of maintaining about 50% of normal milk yield in the absence of prolactin at day 6 of lactation. By day 14 of lactation, anti-rGH treatment alone was capable of decreasing milk yield by about 20%, and again milk secretion only stopped completely when GH and prolactin were suppressed. These data suggest that the role of GH in supporting lactation increases as lactation progresses. The effects of GH in stimulating growth and in increasing milk yield in ruminants have been proposed to be mediated via insulin-like growth factor-I (IGF-I). In rats treated with anti-rGH, both IGF-I and IGF-II were decreased in serum. The concentration of the major IGF-binding protein (IGFBP-3) was not, however, affected by inhibition of GH or prolactin individually, but was decreased in animals treated with bromocriptine and anti-rGH. In animals given both bromocriptine and anti-rGH, concurrent treatment with recombinant bovine GH maintained milk yield at 50% of control values and normalized serum IGF-I, IGF-II and IGFBP-3 concentrations. By contrast, concurrent treatment with IGF-I or IGF-II, despite normalizing their respective concentrations in serum, failed to affect milk yield.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro, insulin-like growth factor-I (IGF-I) promotes both growth and development of bovine mammary tissue. In vivo, the effects of IGF-I may encompass endocrine, paracrine or autocrine mediation. We addressed the possibility of paracrine/autocrine effects of IGF-I in the mammary gland by examining the in-vitro secretion of IGF-I and IGF-binding proteins (IGFBPs) from bovine mammary tissue. Bovine mammary explants from pregnant non-lactating and lactating non-pregnant animals were found to synthesize and secrete IGF-I and IGFBPs. Mammary acini cultures, representative of mammary secretory epithelia, secreted both IGF-I and IGFBP, but synthesized only IGFBP. Concentrations of IGF-I in conditioned media from explants were 1.54 and 0.72 fmol/micrograms DNA for pregnant and lactating animals respectively. Concentrations of IGFBPs in conditioned media from explants were similar for both physiological states at 2529 pmol 125I-labelled IGF-I bound/micrograms DNA. Ligand/Western blotting procedures identified four IGFBPs of 29, 33, 37 and 44 kDa for acini cultures and five IGFBPs of 28, 31, 36, 44 and 46 kDa for explant cultures. Similar affinities for IGF-I and IGF-II were shown by IGFBP, using 125I-labelled recombinant human IGF-I as the competing ligand (median effective dose (ED50) of 0.085 pmol). When 125I-labelled bovine IGF-II was used as the ligand, only bovine IGF-II (ED50 of 0.25 pmol) inhibited binding. The addition of prolactin, insulin and cortisol, with or without GH, did not affect secretion of either IGF-I or IGFBP. This report describes the ability of normal mammary tissue to synthesize and secrete IGF-I and IGFBPs.

The ontogeny and secretory pattern of plasma insulin-like growth factor-I (IGF-I) in relation to GH secretion were studied in meat-type (broiler) poultry during pre-pubertal and post-pubertal growth. Male and female broiler chickens of two commercial strains (strains A and B) were reared from 1 to 198 days of age. From 1 to 49 days of age birds were reared in raised-wire cages and thereafter in deep-litter pens, with food available ad libitum. Blood samples were taken at regular intervals during growth, and at 29 and 43 days of age representative birds were cannulated and serial blood samples taken at 10-min intervals for 5 to 7 h. Plasma concentrations of GH and IGF-I were measured by radioimmunoassay. Birds of strain A were heavier (P less than 0.05) than those of strain B from 12 to 35 days of age. In general, male birds were heavier (P less than 0.01) than females from 12 to 35 days of age. Plasma GH concentrations were significantly higher (P less than 0.05) from 12 to 35 days of age, while plasma IGF-I concentrations were lower (P less than 0.05) from 6 to 21 days of age in male compared with female birds. Plasma IGF-I concentration increased with age, reaching a plateau at 28 days of age, while plasma GH concentration declined over the same period. Plasma IGF-I concentrations declined in a linear manner from 49 to 198 days of age, and there was no evidence of a pubertal increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Human thyroid epithelial cells in monolayer culture were found to release radioimmunoassayable insulin-like growth factor-I (IGF-I) over a 48-h culture period in serum-free medium. In the presence of supraphysiological concentrations of TSH (1-100 mU/ml) known to be inhibitory to DNA synthesis by human thyroid cells, the release of IGF-I was found to be inhibited in six thyroid cultures studied. In only one out of the six was IGF-I release increased in the presence of physiological mitogenic concentrations of TSH (0.1-100 microU/ml). Human thyroid fibroblasts, established by long-term culture of thyroid epithelial cells under fibroblast-selective conditions, also secreted IGF-I which was unaffected by the presence of TSH at both low and high concentrations. Using a monoclonal antibody against human IGF-I, monolayer cultures of both human thyroid epithelial cells and human thyroid fibroblasts showed positive immunocytochemical staining for IGF peptide. However, fixed sections of intact thyroid tissue only showed positive staining for IGF peptide associated with the fibrous layers surrounding the thyroid follicle, with no staining of the follicular epithelial cells. The growth of human thyroid epithelial cells was also found to be increased by IGF-I (25-100 ng/ml) added in medium plus 1% fetal calf serum as assessed by the incorporation of [3H]thymidine into DNA. In the presence of a monoclonal antibody to IGF-I the increase in [3H]thymidine uptake in response to IGF-I was abolished as was that seen in response to TSH.(ABSTRACT TRUNCATED AT 250 WORDS)

The in-vivo biological activity of recombinant methionyl insulin-like growth factor I (met-IGF-I) was demonstrated in hypophysectomized rats by following blood glucose after an i.v. bolus injection of met-IGF-I; a dose-dependent decrease in blood sugar was seen. Membrane transport was studied using the non-metabolizable amino acid alpha-aminoisobutyric acid; stimulation was obtained with the highest dose used (90 micrograms/rat). To test the original somatomedin hypothesis, growth studies were performed in hypophysectomized rats. Two or three doses of met-IGF-I were given with three different administration regimes (i.v. or s.c. infusion, or s.c. injections twice daily) for 6 or 8 days. Little growth-promoting activity was observed, with a significant effect on body weight gain obtained only when met-IGF-I was given continuously at the highest dose used (180 micrograms/day). No effect was seen on the in-vivo uptake of radioactive sulphate into cartilage. Epiphyseal cartilage width increased slightly at the highest dose of met-IGF-I, but only when the hormone was given by infusion. When 180 micrograms met-IGF-I/day were given by injections, a significant effect on longitudinal bone growth was obtained (90 micron above control). The levels of IGF in the serum were not measurably increased after s.c. administration of met-IGF-I, whereas after i.v. infusion, significantly raised levels were obtained at the higher dose rates (3.0 +/- 0.3 and 2.8 +/- 0.1 units/ml). Growth hormone was much more effective than met-IGF-I even at 50-fold lower doses. Priming the animals with 10 mu. bovine GH/day followed by combined infusions of GH and met-IGF-I did not reveal any potentiating effects of met-IGF-I in the presence of GH. We conclude that met-IGF-I is a relatively poor growth-promoting agent when given systemically, and that somatomedins are more likely to act as local growth factors rather than as circulating mediators of the growth-promoting effects of GH.

The effect of insulin-like growth factor-I (IGF-I), epidermal growth factor (EGF), fibroblast growth factor (FGF) and nerve growth factor (NGF) on production of oxytocin and progesterone by cultured bovine granulosa and luteal cells was studied. Secretion of oxytocin was stimulated, in a dose-dependent manner, by IGF-I at 48 and 120 h of culture to levels much higher than those after stimulation with LH, FSH, EGF, FGF or NGF. A similar effect of IGF-I was observed for progesterone but, in contrast to oxytocin, secretion of progesterone was not increased by EGF, NGF or FGF. During primary culture, for 4 h, of dispersed bovine luteal cells obtained from corpora lutea between days 4 and 10 of the oestrous cycle, all the growth factors tested failed to stimulate secretion of oxytocin or progesterone. The data suggest the relevance of growth factors (especially IGF-I) for ovarian physiology and their possible importance for differentiation of follicles and luteinization.

The effect of human GH (hGH) and insulin-like growth factor-I (IGF-I) on colony formation of rabbit epiphyseal tibial chondrocytes at different stages of maturation was studied in suspension culture. The epiphyseal growth plate from the proximal tibia of 8-week-old male rabbits was dissected and divided into three different (proximal, intermediate and distal) zones, each zone representing an enrichment of chondrocytes from the germinative, proliferative and hypertrophic cell layers respectively. Chondrocytes from these three zones were isolated by collagenase digestion and cultured in the presence of 10% (v/v) newborn calf serum in suspension stabilized with 0.5% (w/v) agarose for 14 days. The colonies were classified according to diameter and the number of colonies was estimated as a function of colony size (distribution of cloning efficiency). Cell clusters with a diameter of 56 micron or more were classified as colonies. The cloning efficiency (number of colonies formed per 1000 seeded cells) was 10.1 +/- 0.7 and 6.0 +/- 0.8 for chondrocytes isolated from the proximal and intermediate zones respectively. Insulin-like growth factor-I (25-200 ng/ml) increased the number of colonies in chondrocytes isolated from the proximal zone (122 +/- 9.0-156 +/- 8.4%; control value, 100%) and from the intermediate zone (136 +/- 14.0-191 +/- 29%). Low concentrations of hGH (10-40 ng/ml) stimulated colony formation in chondrocytes isolated from the proximal zone (125 +/- 6.4-137 +/- 7.9%) whereas a high concentration of hGH (160 ng/ml) was ineffective. Chondrocytes isolated from the intermediate zone showed no response to low concentrations of hGH (10-20 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)