Antibody inhibition of vitellogenesis and oocyte maturation in salmon and flounder

Fundulus heteroclitus gonadotropins.5: Small scale chromatographic fractionation of pituitary extracts into components with different steroidogenic activities using homologous bioassays

Fractionation and characterization of gonadotropins (GtH) from Fundulus heteroclitus pituitary extracts were carried out using a biocompatible liquid chromatographic procedure (Pharmacia FPLC system). Chromatographic fractions were monitored for gonadotropic activities (induction of oocyte maturation and steroid production) using homologous follicle bioassays in vitro. Size-exclusion chromatography eluted gonadotropic activity in one major protein peak (Mr approximately 30,000). Anion-exchange and hydrophobic-interaction chromatography (HIC) yielded two distinct peaks of 17beta-estradiol (E2)- and 17alpha-hydroxy,20beta-dihydroprogesterone (DHP)-promoting activity with associated oocyte maturation. Two-dimensional chromatography (chromatofocusing followed by HIC) resolved pituitary extracts into two active fractions; both induced E2 synthesis, but one was relatively poor in eliciting DHP and testosterone production. Thus, using homologous bioassays, at least two quantitatively different gonadotropic (steroidogenic) activities: an E2-promoting gonadotropin (GtH I-like) and a DHP-promoting gonadotropin (GtH II-like), which has a lower isoelectric point but greater hydrophobicity than the former, can be distinguished from F. heteroclitus pituitaries by a variety of chromatographic procedures. This study complements previous biochemical and molecular data in F. heteroclitus and substantiates the duality of GtH function in a multiple-spawning teleost.

Monitoring biological effects of contamination in marine fish along French coasts by measurement of ethoxyresorufin-O-deethylase activity

The use of bioindicators to evaluate exposure to the biological effects of chemical pollutants in marine organisms constitutes a new tool in the monitoring field. The establishment of a North Sea monitoring network in 1991, involving such international organizations as the North Sea Task Force, the International Council for the Exploration of the Sea, and the Intergovernmental Oceanography Commission, led French researchers to develop an enzymatic biomarker to monitor biological effects within the National Observation Network. The biomarker, ethoxyresorufin-O-deethylase (EROD), dependent on the CP450 system, has been monitored biannually since 1992 in several species of fish (Callionymus lyra, Limanda limanda, Serranus sp., Mullus barbatus) in two coastal sites particularly exposed to industrial and domestic pollution. A rapid method is used to assay EROD enzymatic activity determined along a pollution gradient, and results are interpreted on a microplate reader. The strategy of this approach is to assess the effects on the marine ecosystem during prolonged exposure to specific pollutants such as polyaromatic hydrocarbons, polychlorinated biphenyls, and dioxins.

Stimulation of in vitro ovarian estradiol-17 beta synthesis in the rainbow trout by the carbohydrate-poor protein fraction from sockeye salmon pituitary glands

The role of carbohydrate-poor (Con A I) and carbohydrate-rich (Con A II) pituitary protein fractions, isolated from sockeye salmon (Oncorhynchus nerka), were investigated pertaining to in vitro estradiol-17 beta (E2) production by rainbow trout (Oncorhynchus mykiss) ovarian follicles. During the early vitellogenic phase of the reproductive cycle, using defolliculated ovarian follicle preparations (outer epithelium-thecal layer absent), it was demonstrated that the Con A I fraction was capable of increasing E2 production, in the presence of exogenous testosterone (T) as the substrate. Under similar conditions the Con A II fraction (containing the maturational gonadotropin) was inactive. However the Con A II fraction or T, separately, increased E2 production by intact ovarian follicles, whereas the Con A I fraction did not. A mechanism proposed to explain the regulation of ovarian E2 synthesis involves the Con A I fraction enhancing aromatase activity in granulosa cells permitting an increased conversion of T to E2.

Steroidogenesis in rainbow trout (Salmo gairdneri) at various preovulatory stages: changes in plasma hormone levels andin vivo andin vitro responses of the ovary to salmon gonadotropin

In order to specify the timing of some changes in ovarian steroid production during the transition from vitellogenesis to ovulation, plasma hormones levels andin vivo andin vitro responses of the ovary to salmon gonadotropin (s-GtH) or dibutyryl-cyclic adenosine mono-phosphate (db-cAMP) were recorded in relationship with the state of germinal vesicle migration in the oocyte.In vivo, a small, but significant, increase of plasma 17α-hydroxy-20β-dihydroprogesterone (17α, 20β-OH-P) level was detected earlier (at the "subperipheral germinal vesicle" stage) than the increase of GtH level (detectable at the "peripheral germinal vesicle" stage) and the decline of oestradiol-17β (E2-17β) (also detectable at the "peripheral germinal vesicle" stage). Negative correlations were established between E2-17β levels and GtH (ρ=-0.53) or 17α,20β-OH-P (ρ=-0,43) levels while a positive correlation occurred between 17α,20β-OH-P and GtH levels (ρ=+0,54).In vivo no action of GtH on the decline of E2-17β levels was detected GtH did not stimulate 17α,20β-OH-P production, within 72h, in females at the "end of vitellogenesis" stage. It had significant effect in females at other stages closer to ovulation, but the pattern of responses changed according to the stage.In vitro db-cAMP like GtH was able to stimulate 17α,20β-OH-P output from ovarian follicles. The greatest response was observed at the later stage. (GVBD). Testosterone output was also increased by GtH, but the lowest response was observed at the later stage (GVBD). Androstenedione output was lower than testosterone output.In vitro, a small but significant decline of E2-17β output was induced by GtH. We conclude that substantial changes occur during the very last stages prior to ovulation, both in the steroidogenic potential of the ovary and in the ovarian sensitivity to GtH. 20β-oxydoreductase is probably progressively induced during GV migration when GtH basal levels are increasing but still relatively low. Without minimizing the role of discrete pulses of GtH on this induction, we could expect synergic actions of other hormones. Thus a high testosterone/oestradiol ratio in the follicle environment favours 17α,20β-OH-P secretion.

Pituitary extract of the ricefield eel Monopterus albus (Synbranchidae, Teleostei) exhibits gonadotropic activity in the classes Mammalia, Aves, Reptilia and Amphibia

Pituitary extract of the ricefield eel Monopterus albus demonstrated gonadotropic activity in mammals and non-mammalian vertebrates. Using the rat as the recipient, FSH activity was detected in Monopterus pituitaries in the HCG augmentation test and LH activity in the ovarian ascorbic acid depletion test. Cyclic AMP level in superovulated ovaries, ovarian lactate production and glucose uptake in vitro, plasma testosterone level in males, testicular enzymes, ventral prostate weight and other androgen-dependent parameters were stimulated after treatment with Monopterus pituitary extract. Testicular and ovarian 32P5+ uptake in the chick, testicular weight in the grass turtle Chinemys reevesi, and ovulation in the amphibians Xenopus laevis and Rana tigrina were enhanced. Both the FSH-like and LH-like activities in Monopterus pituitaries were sensitive to proteolytic enzymes and chemicals that attack the disulfide linkage, carbohydrate moiety, tyrosine, tryptophan and histidine residues. This constitutes the first report of dual gonadotropic activities elicited by a teleost pituitary extract in the mammal in vivo.

Effect of carp gonadotropin (cGTH) and a fraction unabsorbed on concanavalin A-Sepharose obtained from cGTH on vitellogenesis in the hypophysectomized marine teleost Gobius niger

To investigate whether a differential potency on vitellogenesis exists between the carp gonadotropin (cGTH) and fraction I-cGTH (proteins from cGTH unbound on concanavalin A-Sepharose, which represent 5% of cGTH in weight), hypophysectomized Gobius niger were treated with the two hormonal preparations at the same level. Vitellogenesis was checked for synthesis of vitellogenin and yolk incorporation in the ovary by means of immunological studies and histological techniques (light and electron microscopy). In addition, increased synthesis of vitellogenin was induced by injection of estradiol 17 beta together with each gonadotropin to assess the action of the two hormonal preparations on vitellogenin incorporation. Oogenesis was enhanced by cGTH and fraction I-cGTH, and at the same dose levels both treatments produced a similar pattern of stimulation of vitellogenesis. Vitellogenin was found in all the blood samples of animals treated by the hormones (cGTH and fraction I-cGTH) alone. Vesicles of pinocytosis were detected by electron microscopy up to Stage IIIa of oogenesis. When a high synthesis of vitellogenin was induced by exogeneous estradiol 17 beta injections, the two gonadotropic preparations had similar effects in yolk incorporation. cGTH was not less potent than fraction I-cGTH in these processes even though the cGTH preparation contains only 5% of fraction I-cGTH. The contamination of cGTH by a small amount of material unbound on concanavalin cannot be solely responsible for the vitellogenic activity of cGTH which consists of 95% glycoproteins.

Plasma vitellogenin in landlocked Atlantic salmon (Salmo salar Ouananiche): isolation, homologous radioimmunoassay and immunological cross-reactivity with vitellogenin from other teleosts

Vitellogenin was isolated by affinity chromatography and gel filtration from landlocked Atlantic salmon plasma. Vitellogenin was labelled with iodine-131 using iodogen and an homologous radioimmunoassay was developed. There was poor immunological cross-reactivity with vitellogenin or plasma from other teleosts. Parallelism of the vitellogenin standard to the displacement by plasma of vitellogenic salmon allowed the assay to be used to evaluate the seasonal concentration profile of vitellogenin in female adult salmon. Extracts of liver or ovary from female Atlantic salmon also yielded displacements parallel to the vitellogenin standard in the assay.

Failure of antibody to carbohydrate-rich gonadotropin to inhibit rapid ovarian growth in landlocked Atlantic salmon

The discovery of a carbohydrate-poor gonadotropin has resulted in a reassessment of the role of the classical, carbohydrate-rich gonadotropin (Con A II GtH) in teleost ovarian development. Prolonged treatment of landlocked Atlantic salmon with antibody to Con A II GtH failed to inhibit rapid ovarian growth or accumulation of triglyceride or vitellogenin derivative. Sera from antibody-treated fish showed substantial capacity to bind Con A II GtH indicating that antibody treatment successfully removed endogenous Con A II GtH from the circulation. These results are consistent with previous reports that a factor other than Con A II GtH is responsible for stimulating yolk accumulation.

Stimulation in vitro of estradiol secretion by the ovary of a cichlid fish, Sarotherodon aureus

The objective of the present study was to investigate the nature of the gonadotrophic stimulation of estradiol (E2) secretion by the ovary of a teleost fish in vitro. Spontaneous output of E2 decreased to a low baseline after 3 hr of superfusion and increased to a maximal level 2-3 hr after the introduction of homologous pituitary extract (T-PE) or human chorionic gonadotrophin into the superfusion system. Addition of the phosphodiesterase inhibitor, isobutyl methylxanthine (IBMX, 0.5 mM), into a closed-system incubation resulted in an augmented response of the ovary to either dibutyryl cyclic AMP or to T-PE. It is concluded that the gonadotrophic stimulation of E2 secretion from the ovary of Sarotherodon aureus is mediated by cyclic AMP as a second messenger. Purified carp GTH or ovine LH stimulated E2 secretion in vitro in a dose-dependent manner in the range 3-300 ng/ml. In order to examine the effect of ovarian stage on E2 secretion rate in response to a gonadotrophic stimulation, fish with regressed ovaries were transferred to 30 degrees for 29 days. Five fish were bled every 4 days and their ovaries were incubated individually with and without T-PE. A sevenfold increase in plasma E2 occurred 4 days after the transfer to 30 degrees, whereas the first significant increase in the gonadosomatic index (GSI) could be noted only on Day 12. Both the spontaneous secretion rate of E2 in vitro (E2 basal) and the secretion rate in response to T-PE (E2 max) increased together with the GSI throughout the experiment. However, the ratio E2 max/E2 basal, which reflects the capacity of the ovary to respond to the gonadotrophic stimulation, reached a peak on Day 16, when GSI was about 1. The ratio then declined and remained low until the end of the experiment. The early increase in plasma E2 can be explained by the elevated sensitivity of the ovary to GTH during the initial phase of the temperature-induced ovarian recrudescence. The high level of plasma E2 maintained from Day 16 on may be due to a spontaneous synthesis and secretion of the steroid, not necessarily controlled by GTH.

Impairment of early ovarian growth in landlocked Atlantic salmon by an antibody to carbohydrate-rich gonadotropin

The role of the carbohydrate-rich gonadotropin (Con AII GtH) in an early phase of ovarian growth in landlocked Atlantic salmon (Salmo salar) was investigated by treating in vivo with an antibody to chum salmon (Oncorhynchus keta) Con AII GtH (anti-Con AII). Anti-Con AII treatment significantly inhibited ovarian growth but did not consistently lower serum levels of vitellogenin. This suggests that Con AII GtH is necessary for early ovarian growth and, has one or more functions in early ovarian growth in addition to stimulation, via estrogen, of vitellogenin production.

[Maturational glycoprotein gonadotropin and estradiol-17-beta during the reproductive cycle of the female brown trout (Salmo trutta)]

Female brown trout were sacrificed every month or twice a month during the reproductive season. Plasma gonadotropin (GtH) and estradiol-17 beta (E2-17 beta) were measured using radioimmunological techniques, in relation with the state of gametogenesis. From ovulation to July egg's diameters remained less than 1 mm, and ovogenesis was characterized from the histological appearance of three types of vitellus: glycoproteique (type I), lipidique (type II), lipidoprotéique (type III), and the immunological plasma detection of the vitellogenin. During this period GtH levels remained lower than 1 ng/ml except in March, when they increased around 5 ng/ml, both with pituitary GtH and plasma E2 17 beta. This rise occurred just before the appearance of the type III vitellus within the oocyte, and might correspond to a critical phase of the reproductive cycle during which vitellogenin could not be detected in 70% of the animals. During rapid growth of the oocyte from 1 to 5 mm, mean GtH levels increased from 0.75 to 2.5 ng/ml when those of the E2-17 beta increased more rapidly but began to drop before the end of vitellogenesis. Maturation and ovulation were accompanied by a rise of the GtH level, in correlation with the lower levels of E2-17 beta measured during the cycle, GtH remained high even after ovulation, and more in fish which had kept their eggs within the body cavity. Correlation among GtH, E2-17 beta, and the diameters of eggs had been calculated. There was a positive correlation among GtH, E2-17 beta levels, and the diameters of eggs during exogenous vitellogenesis, and a negative between GtH and E2-17 beta at the end of the reproductive cycle. These results were discussed, in relation to the existence of a pulsatile mode of GtH secretion.