共查询到20条相似文献，搜索用时 840 毫秒
1.
Yongjiang Xu Bin Wang Xuezhou Liu Bao Shi Kun Zang 《Fish physiology and biochemistry》2017,43(2):527-537
Although gonadotrophins are major regulators of ovarian function in teleosts and other vertebrates, accumulating evidence indicates that the growth hormone (GH)-insulin-like growth factor (IGF) axis also plays an important role in fish reproduction. As a first step to understand the physiological role of the GH-IGF system in the ovarian development of starry flounder (Platichthys stellatus), the expression profiles of GH and IGF messenger RNAs (mRNAs) and plasma GH, IGF-I, estradiol-17β (E2), and testosterone (T) levels during the ovarian development were investigated. The developmental stages of ovaries were divided into five stages (II, III, IV, V, and VI) by histological analysis. The hepatosomatic index (HSI) and gonadosomatic index (GSI) values increased and peaked at stage IV and stage V, respectively, and then declined at stage VI. Pituitary GH mRNA levels decreased sharply at stage III and raised to top level at stage VI. The hepatic IGF-I mRNA levels ascended to maximum value at stage V and then declined significantly at stage VI. However, the hepatic IGF-II mRNA levels remained stable and increased significantly at stage VI. In contrast, the ovarian IGF-I mRNA levels increased gradually and peaked at stage VI. The ovarian IGF-II mRNA levels were initially stable and increased significantly at stage V until the top level at stage VI. Consistent with the pituitary GH mRNA levels, plasma GH levels reduced sharply at stage III and remained depressed until stage V and then raised remarkably at stage VI. Plasma IGF-I level peaked at stage V and then declined to initial level. Plasma E2 level peaked at stage IV and then dramatically descended to the basal level. Plasma T level peaked at stage V and then declined significantly back to the basal level. Based on statistical analysis, significant positive correlations between hepatic IGF-I mRNA and GSI, ovarian IGF-II mRNA and hepatic IGF-II mRNA, ovarian IGF-I mRNA and ovarian IGF-II mRNA, and plasma IGF-I and plasma T were observed, respectively. These results suggest that the GH-IGF system may be involved in the ovarian development of starry flounder; GH and IGFs appear to play distinct roles in the regulation of the ovarian development in paracrine/autocrine manners. These findings extend our knowledge of the roles of the GH-IGF axis on reproduction regulation in fish. 相似文献
2.
The tilapia, Oreochromis mossambicus, exhibits a sexually dimorphic pattern of growth, males growing larger than females. We examined the effects of E2 and DHT on the GH/IGF-I axis and on VTG production in the tilapia. Sexually mature tilapia were injected with 5 μg g body
weight of E2 (males) or DHT (females) every 5 days for a total of 3 injections. Female tilapia had significantly higher plasma GH levels
than males. However, plasma and liver mRNA levels of IGF-I were significantly lower in females than in males, whereas VTG
levels in both the plasma and liver mRNA were significantly higher in females than in males. Although significant amounts
of VTG were detected in control males (8 ± 0.3 μg ml), the levels in control females (3000 ± 500 μg ml) were about 400 times
higher than in males. Males treated with E2 exhibited a female-like GH/IGF-I profile. That is, they had significantly elevated levels of plasma GH with lower plasma
IGF-I and liver IGF-I mRNA levels. Estradiol treatment significantly elevated both plasma and liver mRNA VTG levels. Dihydrotestosterone
treatment in females induced a male-like GH/IGF-I profile: plasma GH levels were significantly reduced, whereas plasma and
liver IGF-I mRNA levels were significantly elevated. Both plasma and liver mRNA levels of VTG were not altered by DHT treatment.
Pituitary GH mRNA levels were similar in all treatment groups. These results clearly indicate that estrogens and androgens
feminize and masculinize the GH/IGF-I axis, respectively.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
S. Kajimura K. Uchida T. Yada L.G. Riley J.C. Byatt R.J. Collier K. Aida T. Hirano E.G. Grau 《Fish physiology and biochemistry》2001,25(3):221-230
We have previously reported growth-promoting effects of recombinant bovine growth hormone (rbGH) in Mozambique tilapia, Oreochromis mossambicus, after 4 weekly injections or a single injection of slow-releasing formulation (Posilac®) (Leedom et al. 2002). In order to obtain further understanding of the role of the growth hormone (GH)-insulin-like growth factor-I (IGF-I) axis in growth in the tilapia, the effects of rbGH on plasma and mRNA levels of IGF-I were examined. Plasma IGF-I levels were significantly increased after rbGH and Posilac® injections, and a significant correlation was observed between plasma IGF-I levels, body length and mass in both treatments. IGF-I mRNA levels in the liver and in the skeletal muscle were also significantly increased after rbGH and Posilac® injections, indicating that IGF-I gene expression in these tissues is under control of circulating GH. IGF-I mRNA levels in the gill were not affected by treatment. Liver IGF-I mRNA levels were significantly correlated with body length and with body mass after rbGH and Posilac® injections. These results indicate that the growth-promoting effect of rbGH in this species is mediated to a significant extent via its stimulation of hepatic production of IGF-I and the resulting increase in plasma IGF-I, and also possibly through locally produced IGF-I in the skeletal muscle, acting in a paracrine or autocrine fashion. 相似文献
4.
为深入认识半滑舌鳎(Cynoglossus semilaevis)生殖调控机制,研究了生长轴(GH/IGF-Ⅰ axis)对半滑舌鳎卵巢发育调控的作用及可能机制;分析了卵巢不同发育时期垂体中的生长激素(GH),脑、性腺和肝脏中的类胰岛素生长因子Ⅰ (IGF-Ⅰ)mRNA的表达水平变化;检测了卵巢不同发育期,血清GH、IGF-Ⅰ、雌二醇(E2)、睾酮(T)的表达水平变化,并分析了生长因子与性腺指数(GSI)、E2和T表达变化的关系.结果显示,垂体GH mRNA表达水平在Ⅳ期卵巢时显著升高,至Ⅴ期时达峰值,随后(Ⅵ期)显著降低,垂体GH mRNA表达水平与GSI、血清GH与IGF-Ⅰ表达水平呈显著正相关.血清GH与垂体GHmRNA表达水平表现出相似的变化趋势.肝脏IGF-ⅠmRNA表达水平在Ⅳ期和Ⅴ期卵巢时较低,但Ⅵ期时又显著升高,其与脑IGF-Ⅰ mRNA及血清IGF-Ⅰ表达水平呈显著正相关,而与血清E2和T表达水平呈显著负相关.脑IGF-Ⅰ mRNA表达水平自Ⅱ期卵巢开始显著升高,至Ⅳ期时达峰值,并与血清IGF-Ⅰ表达水平呈显著负相关.卵巢IGF-ⅠmRNA表达水平自Ⅱ期开始显著升高,并在Ⅳ期时达峰值,但在Ⅴ期时明显下降,并保持至Ⅵ期,与血清E2表达水平呈显著正相关,而与血清IGF-Ⅰ表达水平呈显著负相关.血清IGF-Ⅰ变化趋势与肝脏IGF-ⅠmRNA相似.结果揭示了GH、IGF-Ⅰ在转录和血清水平上以协同或者拮抗的方式共同参与了半滑舌鳎卵巢发育的过程,其作用途径可能与性类固醇激素的合成与分泌有关,表明GH/IGF-Ⅰ轴对卵巢发育具有重要的调控作用,为深入认识半滑舌鳎卵巢发育的调控机制提供了新的思路和素材. 相似文献
5.
The role of growth hormone (GH) in regulating hepatic mRNA expression of insulin-like growth factor-I (IGF-I) and IGF binding
proteins (IGFBPs) in yellowtail Seriola quinqueradiata was examined using in vivo and in vitro assays. Yellowtail hepatic IGF-I, IGFBP-1, IGFBP-2, IGFBP-3, and IGFBP-5 mRNAs were
measured by real-time quantitative RT-PCR. Intraperitoneal injection of recombinant GH of chum salmon Oncorhynchus keta (rsGH) at a dose of 1 μg/g body weight resulted in a significant increases in hepatic IGF-I, IGFBP-3, and IGFBP-5 mRNA levels,
whereas significant reductions in hepatic IGFBP-1 and IGFBP-2 mRNA levels were observed. For in vitro assays, liver slices
were incubated with rsGH at different concentrations (doses: 0, 1, 10, 100, 500, and 1,000 ng/ml). Liver slices incubated
with 100 ng/ml rsGH elicited a significant increase in IGF-I mRNA level. Similarly, a slight increase in IGFBP-3 and IGFBP-5
mRNA levels were also observed in liver explants incubated with rsGH. In contrast, a significant decline in IGFBP-1 mRNA levels
was observed in liver slices incubated with 1,000 ng/ml rsGH. A slight decline in the level of IGFBP-2 mRNA was noted in liver
explants with rsGH treatment. This study demonstrates the modulating effect of GH on the IGF system. 相似文献
6.
7.
8.
Amir Abbas Bazyar Lakeh Hamid Farahmand Werner Kloas Alireza Mirvaghefi Achim Trubiroha Brian C. Peterson Sven Wuertz 《Aquaculture International》2016,24(1):11-21
Juvenile rainbow trout (Oncorhynchus mykiss) were passively immunized by intraperitoneal immunization against somatostatin-14 (SS-14) using an antibody originating from egg-laying chicken (Gallus domesticus). Fish were immunized weekly (0, 7, 14, 21, 28, 35 days) with chicken egg yolk-derived immunoglobulin (IgY) against SS-14 (1:25 IgY, 5 mg mL?1), and growth performance, feed utilization as well as plasma concentrations and mRNA levels of growth hormone (GH) and insulin-like growth factor I (IGF-I) were compared to the control group that received placebo immunization with PBS. Passive immunization significantly increased weight gain of treated fish (67.7 ± 7.4 g) compared to the control group (40.1 ± 2.0 g) after 35 days (p < 0.05). Feed conversion ratio (FCR) was significantly improved in the immunized fish (0.7 ± 0.08) compared to control group (1.2 ± 0.06) (p < 0.05). The concentrations of GH and IGF-I in the blood plasma showed no significant differences between the fish treated with anti-SS-14 and those of control during the treatment (p > 0.05). In both groups, GH levels decreased over the 35 days of the experiment (p < 0.05). However, IGF-I level during the period of treatment remained unchanged in both control and immunized fish with the anti-SS-14. Similarly, no changes were observed in pituitary GH and liver IGF-I mRNA levels between treatment and control at each sampling time (p > 0.05). There was no indication of a cumulative, long-lasting effect of repeated immunization on GH or IGF-I plasma concentrations or mRNA expression. The present study shows that a passive immunization of rainbow trout against SS-14 using a chicken egg yolk-derived SS-14 antibody could increase growth rate and improved FCR. 相似文献
9.
10.
11.
Growth hormone (GH) has recently been identified as co-gonadotropin regulating fish reproduction, hitherto, no effort has
been made to see its effect on oocyte maturation in fishes, though some reports demonstrate the role of insulin like growth
factor-I (IGF-I) in oocyte maturation in teleosts. Hence, effect of GH on oocyte maturation in post-vitellogenic H. fossilis has been worked out in the present study. Post-vitellogenic follicles in the ovarian tissue were challenged in vitro with H. fossilis pituitary homogenate (fPH), Clarias batrachus GH and GtH, barramundi IGF-I (IGF-I), 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) and testosterone alone, or in combination with IGF-I for 18 h at 26±1°C. Incubation of ovarian
tissue with GH in the presence of actinomycin d or cycloheximide or barramundi IGF-I antiserum was also made separately. In general, oocyte maturation was induced by fPH,
barramundi IGF-I, GtH, GH and DHP, which was augmented further by addition of barramundi IGF-I. Testosterone had no effect
on GVBD. Actinomycin d, cycloheximide and anti barramundi IGF-I abolished the GH induced oocyte maturation. Present study suggests for the first
time that GH has a role in egg maturation in fish. 相似文献
12.
Shunsuke Moriyama Kiyoko Yamaguchi Tomomi Takasawa Hiroaki Chiba Hiroshi Kawauchi 《Fish physiology and biochemistry》2006,32(3):189-201
In an attempt to understand growth regulation in the Japanese eel, Anguilla japonica, we cloned insulin-like growth factor-I (IGF-I) cDNAs and examined their mRNA expression in several tissues. Two eel IGF-I (eIGF-I) cDNAs encoding preprohormones, eIGF-I-Ea1and eIGF-I-Ea2, were cloned from the liver by polymerase chain reaction (PCR). The preproIGF-Is were identical in signal peptide and mature IGF-I, but different in the E domain—eIGF-I-Ea2 mRNA was 36 bp longer than eIGF-I-Ea1 mRNA. Eel IGF-I was 83–94% identical with that of teleosts, 71% identical with that of dogfish, 87% identical with that of bullfrog and chicken, and 83% identical with that of humans. In both males and females the highest eIGF-I-Ea1 mRNA levels were observed in the liver, with detectable levels also found in the gills, heart, stomach, spleen, kidney, intestine, swim-bladder, muscle, and gonads. eIGF-I-Ea1 mRNA levels in the liver were higher in females than in males whereas in the intestine they were lower than in males. eIGF-I-Ea2 mRNA was detected in all the tissues examined and at similar levels in males and females. In this experiment higher eIGF-I-Ea1 mRNA levels were observed in the liver of larger glass eels than in those of smaller fish. eIGF-I-Ea2 mRNA levels were also higher in larger eels, although they were lower than IGF-I-Ea1 mRNA levels. Both eIGF-I mRNA levels in liver were positively correlated with the body size of the␣glass eels. Intraperitoneal injection of recombinant eel GH (reGH), 0.25 μg g−1 body weight, into glass eels resulted in a significant increase in both eIGF-I mRNAs in the liver 1 day after injection compared with control fish, but no elevation was observed 2 days after injection. Incubation of liver slices with reGH at concentrations of 10, 100, and 1,000 ng mL−1 for 24 h resulted in a significant concentration-dependent increase in the levels of both eIGF-I mRNAs. Higher levels of eIGF-I-Ea1 and Ea2 mRNA were observed in the gills ofseawater-reared eels than in those of freshwater-reared fish, but no differenceswere observed in the whole kidney. These results suggest that IGF-I is involved in the regulation of somatic growth and also in adaptation of the Japanese eel to seawater. 相似文献
13.
14.
Insulin-like growth factors I and II (IGF-I and IGF-II) are two highly homologous mitogenic peptides that are expressed ubiquitously and show diverse effects on development, growth, and metabolism. The cDNA encoding IGF-I of a teleost, the orange spotted grouper (Epinephelus coioides) was produced from liver by RT-PCR, and rapid amplification of cDNA ends, RACE. Typically, the deduced 186 amino acid protein contains a signal peptide, B, C, A, D and E domains. On the amino acid level, grouper IGF-I shares 97.3% similarity with black seabream (Sparus macrocephalus) with the differences focusing on the B and C domains. The analysis of the E domain showed that grouper IGF-I belonged to Ea-4 type. When mature amino acid sequence was compared with other vertebrates, it revealed higher similarity with black seabream and halibut, while lower similarity with human and mouse. The expression of IGF-I mRNA in adult tissues was studied using RT-PCR. IGF-I mRNA expression level in the liver was significantly higher than those in the brain and muscles. In other tissues, low amount of IGF-I mRNA expression was also detected. The coding region of IGF-I cDNA for mature IGF-I protein was subcloned into an expression plasmid pTRX and fused with E. coli thioredoxin (Trx). Moreover, we have successfully developed an expression system in E. coli to overproduce recombinant grouper IGF-I. Using western blotting, we found that the fusion protein could blot with antiserum to barramundi IGF-I further confirming the immunoactivity of the recombinant IGF-I. 相似文献
15.
Osmoregulatory actions of growth hormone and its mode of action in salmonids: A review 总被引：8，自引：0，他引：8
Tatsuya Sakamoto Stephen D. McCormick Tetsuya Hirano 《Fish physiology and biochemistry》1993,11(1-6):155-164
Osmoregulatory actions of growth hormone (GH) and its mode of action in salmonids are reviewed. We present evidence suggesting
that insulin-like growth factor I (IGF-I) mediates some of the actions of GH on seawater acclimation. Plasma concentration
and turnover of GH rise following exposure to seawater. Exogenous GH (in vivo) increases gill Na+,K+-ATPase activity and the number of gill chloride cells, and inhibits an increase in plasma osmolarity and ions following transfer
of fish to seawater. A single class of high affinity GH receptors is present in the liver, gill, intestine, and kidney. The
levels of IGF-I mRNA in the liver, gill and kidney increased after GH-injection. After transfer to seawater, IGF-I mRNA increased
in the gill and kidney following the rise in plasma GH, although no significant change was seen in the liver. Injection of
IGF-I improved the ability of the fish to maintain plasma sodium levels after transfer to seawater. GH treatment also sensitizes
the interrenal to adrenocorticotropin (ACTH), increasing cortisol secretion. Both cortisol and IGF-I may be involved in mediating
the action of GH in seawater adaptation, although studies on the effect of GH on osmoregulatory physiology of non-salmonid
species are limited. An integrated model of the osmoregulatory actions of GH is presented, and areas in need of research are
outlined.
Résumé Cet article est une revue des effets osmorégulateurs de l'hormone de croissance et de son mode d'action. Nous présentons des résultats qui suggèrent que le facteur de croissance de type insuline (IGF-I) est un médiateur de certaines des actions de la GH sur l'adaptation à l'eau de mer. Les concentrations plasmatiques et le renouvellement de la GH augmentent après transfert en eau de mer. La GH exogène stimule (in vivo) l'activité Na+,K+-ATPase et le nombre de cellules à chlorure branchialeset inhibe les augmentations de l'osmolarité et des concentrations ioniques du plasma observées après transfert en eau de mer. Une seule classe de récepteurs à haute affinité pour la GH est présent dans le foie, les branchies, l'intestin et le rein. Les niveaux d'ARNm d'IGF dans le foie, les branchies et le rein augmentent après injection de la GH. Après transfert en eau de mer, les ARNm de l'IGF augmentent dans les branchies et dans le rein en suivant l'augmentation de GH plasmatique, bien qu'aucune modification ne soit observée au niveau du foie. L'injection d'IGF augmente la capacité du poisson à maintenir ses niveaux de sodium plasmatique après transfert en eau de mer. Le traitement à la GH augmente la sensibilité à l'adrenocorticotropine (ACTH) et stimule donc les niveaux de cortisol. A la fois le cortisol et l'IGF-I semblent impliqués comme médiateurs des effets de la GH dans l'adaptation à l'eau de mer, bien que les études sur les effets de la GH sur la physiologie de l'osmorégulation chez les espèces non-salmonidés restent encore limitées. Un modèle intégré des actions de la GH sur l'osmorégulation est présenté et les domaines de recherche à développer sont soulignés.相似文献
16.
17.
《Aquaculture (Amsterdam, Netherlands)》2006,251(2-4):585-595
IGF-I is a mitogenic polypeptide that is an important regulator of growth in fish. The potential of IGF-I mRNA abundance as a rapid growth indicator in the Nile tilapia, Oreochromis niloticus, was evaluated. Hepatic IGF-I cDNA was isolated and partially cloned. The partial sequence having 539 bases encodes for the signal peptide, mature protein and a portion of the E domain. The deduced 68 amino acid sequence for mature IGF-I showed 84–90% and 77–79% sequence identity with fish and mammalian counterparts, respectively. The deduced amino acid sequence for domains B and A was most conserved (93–97%) relative to other fishes. A sensitive TaqMan real time qRT-PCR assay for O. niloticus was developed based on the mature IGF-I peptide for measures of hepatic IGF-I mRNA levels. Hepatic IGF-I mRNA levels were found to be significantly correlated with growth rate of fish reared under different feeding regimes and temperature conditions. Higher feed consumption and water temperature produced faster-growing fish and increased hepatic IGF-I mRNA expression. These findings suggest that hepatic-derived IGF-I plays a key role in controlling growth in O. niloticus and indicates that IGF-I mRNA quantification could prove useful for the rapid assessment of growth rate in this species. 相似文献
18.
Cumming Duan Stephen J. Duguay Erika M. Plisetskaya 《Fish physiology and biochemistry》1993,11(1-6):371-379
To examine the hormonal and nutritional regulation of insulin-like growth factor I (IGF-I) mRNA expression, a sequence-specific
solution hybridization/RNase protection assay for coho salmon IGF-I mRNA was developed. This assay is both rapid and sensitive
and has low inter- (less than 15%) and intra-assay variations (less than 5%). Using this assay, the tissue distribution of
IGF-I mRNA and effects of growth hormone (GH), prolactin (PRL) and somatolactin (SL) on hepatic IGF-I mRNA expression in coho
salmon were examined in vivo. Liver had the highest IGF-I mRNA level of 16 pg/μg DNA. Significant amounts of IGF-I mRNA were also found in all other tissues
examined (intestine 4.1, kidney 3.8, gill arch 2.4, brain 2.4, ovary 2.3, muscle 2.1, spleen 1.7 and fat 1.1 pg/μg DNA). Injection
of coho salmon GH at doses of 0.1 and 1 μg/g body weight significantly increased the hepatic IGF-I mRNA levels in a dose-dependent
manner. Injection of coho salmon SL, a recently discovered member of the GH/PRL family, stimulated the IGF-I mRNA expression
at the higher dose (1 μg/g), whereas coho salmon PRL had no effect at either dose. Concentration-dependent stimulation by
coho salmon GH was also obtained in vitro in primary culture of salmon hepatocytes in concentrations ranging from 0.01 to 1 μg/ml. These results indicate that IGF-I
mRNA expression occurs in a variety of tissues in coho salmon, and that at least the hepatic expression is under the regulation
of GH and possibly other hormones. The sequence-specific assay established in the present study can be used for accurate quantitation
of IGF-I mRNA in salmonid species, and can contribute to a better understanding of the physiology of IGF-I in salmonids.
Résumé Afin d'étudier les régulations homronales et nutritionnelles de l'expression des ARNm de l'IGF-I (insulin-like growth factor I), un dosage spécifique par hybridation en solution des ARNm d'IGF-I de saumon coho et protégé des RNases, a été développé. Ce dosage, à la fois rapide et sensible, présente un faible coefficient de variation inter- (< 15%) et intra- (< 5%) dosage. L'étude de la distribution tissulaire des ARNm de l'IGF-I et des effets de l'hormone de croissance (GH), de la prolactine (Prl) et de la somatolactine (SI) sur l'expression hépatique des ARNm de l'IGF-I, a été entreprise in vivo chez le saumon coho en utilisant ce dosage. Le foie présente les plus grandes quantités d'ARNm d'IGF-I (16 pg/μg d'ADN). Des quantités significatives d'ARNm d'IGF-I ont été également détectées dans tous les autres tissus étudiés (intestin 4,1; rein 3,8; branchie 2,4; ovaire 2,3; muscle 2,1; rate 1,7 et graisse 1,1 pg/μg d'ADN). L'injection à des saumons coho, de GH à des doses de 0,1 et 1 μg/g de poids vif, augmente significativement et de manière dose dépendante les niveaux hépatiques d'ARNm d'IGF-I. L'injection de SI de saumon coho, un membre récemment découvert de la famille GH/Prl, stimule avec la plus haute dose utilisée, l'expression des ARNm d'IGF-I alors que la Prl n'a aucun effet. La GH augmente de manière dose dépendante (0,01–1 μg/ml) l'expression in vitro des ARNm d'IGF-I par des ARNm d'IGF-I par des hépatocytes de saumon coho en culture. Ces résultats indiquent que, chez le saumon coho, l'expression des ARNm d'IGF-I est présente dans le nombreaux tissus et que, l'expression hépatique est, au moins en partie, régulée par la GH et peut-être par d'autres hormones. Le dosage par séquence spécifique mise au point dans le présent travail, peut-être utilisé pour la quantification précise des ARNm, d'IGF-I de salmonidés et devrait permettre une meilleure connaissance de la physiologie de L'IGF-I chez les salmonidés.相似文献
19.
Somatostatins (SS) are a structurally diverse family of peptide hormones that affect various aspects of growth, development and metabolism in vertebrates. Fish have proved to be useful models for understanding the role(s) of SS in the regulation of growth. Organismal growth is inhibited by SS and fish with impaired growth (caused by fasting or premature transfer to seawater of anadromous species) display enhanced SS production and elevated plasma levels of the hormone. Somatostatins modulate growth at the level of the pituitary through the inhibition of growth hormone (GH) synthesis and secretion. There are, however, significant structure-function relationships with regard to GH inhibition. For example, while SS-14 is a potent inhibitor of GH secretion, catfish SS-22 and salmonid SS-25 appear not to have GH secretotropic effects. Somatostatins also have extra-pituitary effects on growth. For example, SS reduce GH binding capacity and inhibit IGF-I mRNA expression in the liver. In addition, SS inhibit insulin, another factor essential to organismal growth. Finally, SS interact with a variety of reproductive and metabolic processes - actions which suggest that SS help modulate energy partitioning among biological processes. 相似文献
20.
Recent evidence has indicated the presence of IGF-I and IGF-I receptors in mammalian and teleost ovarian follicles. Since growth hormone (GH), which can be secreted from the pituitary concomitant with a gonadotropin as a response to gonadotropin-releasing hormone, generally acts to release IGF-I from tissues including the ovary, the effect of IGF-I itself on ovarian steroidogenesis and oocyte maturation was investigated in the model teleost, Fundulus heteroclitus. IGF-I was found to be without effect on ovarian follicle steroidogenesis, but initiated oocyte maturation in a dose-dependent manner even more rapidly and effectively than 17,20-dihydroxy-4-pregnene-3-one (DHP), the naturally occurring maturation-inducing steroid. IGF-II also induced oocyte maturation in a dose-dependent manner. IGF-I induction of oocyte maturation occurred in the absence of DHP production by the granulosa cells (which is normally stimulated by gonadotropin), and could be inhibited by cycloheximide but not actinomycin D, thus implicating the role of protein synthesis. These results suggest that GH-stimulated release of ovarian IGF-I may have an even more direct role than DHP on the reinitiation of oocyte maturation. 相似文献