Trout steroidogenic testicular cells in primary culture. I. Changes in free and conjugated androgen and progestagen secretions: effects of gonadotropin, serum, and lipoproteins

Effects of produced water on reproductive parameters in prespawning Atlantic cod (Gadus morhua)

Produced water (PW) discharged from offshore oil industry activities contains substances that are known to contribute to a range of mechanisms of toxicity. In the present study selected reproductive biomarkers were studied in prespawning Atlantic cod (Gadus morhua) exposed to PW. The fish were exposed for 12 wk within a continuous flow-through system at realistic environmental near-field concentrations. Concentrations of polyaromatic hydrocarbon (PAH) and alkylphenol (AP) compounds were analyzed by gas chromatography with mass spectrometric detection measurement, as were PAH and AP metabolites in fish bile for verification of exposure conditions and presence of compounds in PW. A suite of reproductive biomarkers (vitellogenin, zona radiata protein, and plasma steroid concentrations) and histological alterations of the gonads were determined. Results showed that exposure to sufficiently high levels of PW produced an increase in vitellogenin levels in female fish compared to the control. Impaired oocyte development and reduced estrogen levels were also observed in PW-exposed female fish. In male fish testicular development was altered, showing a rise in amount of spermatogonia and primary spermatocytes and a reduction in quantity of mature sperm in the PW-exposed fish compared to control. Data indicate that sufficiently high levels of PW have the potential to adversely affect the reproductive fitness of cod.

The role of the maturation-inducing steroid, 17,20beta-dihydroxypregn-4-en-3-one, in male fishes: a review

The major progestin in teleosts is not progesterone, as in tetrapods, but 17,20beta-dihydroxypregn-4-en-3-one (17,20beta-P) or, in certain species, 17,20beta,21-trihydroxy-pregn-4-en-3-one (17,20beta,21-P). Several functions for 17,20beta-P and 17,20beta,21-P have been proposed (and in some cases proved). These include induction of oocyte final maturation and spermiation (milt production), enhancement of sperm motility (by alteration of the pH and fluidity of the seminal fluid) and acting as a pheromone in male cyprinids. Another important function, initiation of meiosis (the first step in both spermatogenesis and oogenesis), has only very recently been proposed. This is a process that takes place at puberty in all fishes and once a year in repeat spawners. The present review critically examines the evidence to support the proposed functions of 17,20beta-P in males, including listing of the evidence for the presence of 17,20beta-P in the blood plasma of male fishes and discussion of why, in many species, it appears to be absent (or present at low and, in some cases, unvarying concentrations); consideration of the evidence, obtained mainly from in vitro studies, for this steroid being predominantly produced by the testis, for its production being under the control of luteinizing hormone (gonadotrophin II) and, at least in salmonids, for two cell types (Leydig cells and sperm cells) being involved in its synthesis; discussion of the factors involved in the regulation of the switch from androgen to 17,20beta-P production that seems to occur in many species just at the time of spermiation; discussion of the effects of in vivo injection and application of 17,20beta-P (and closely related compounds) in males; a listing of previously published evidence that supports the proposed new function of 17,20beta-P as an initiator of meiosis; finally, discussion of the evidence for environmental endocrine disruption by progestins in fishes.

Effects of a phytosterol mixture on male fish plasma lipoprotein fractions and testis P450scc activity

Plant sterols (phytosterols) have been identified as one potential source of reproductive effects in fish living downstream of pulp mills. beta-Sitosterol, the predominant plant sterol in pulp mill effluent, has previously been shown to decrease plasma sex steroid and cholesterol levels and in vitro gonadal steroid production in fish. In this study, male brook trout (Salvelinus fontinalis) and goldfish (Carassius auratus) were exposed to a phytosterol mixture (72% beta-sitosterol) via Silastic intraperitoneal implants to help elucidate the mechanisms of action of phytosterols on steroid depression. As cholesterol is exogenously supplied for gonadal steroidogenesis, changes in plasma cholesterol fractions were examined. In male brook trout, low-density lipoprotein cholesterol and triglyceride levels decreased significantly, 43 and 50%, respectively, in phytosterol-treated fish. It is improbable, however, that these decreases are linked to depressed gonadal steroidogenesis in fish. The activity of P450scc, which converts cholesterol to pregnenolone (the first step in the steroidogenic pathway), was not affected in testis mitochondria isolated from brook trout or goldfish. Further investigation of the mechanisms of action of phytosterols is required.

Spermatogonia of rainbow trout: III. In vitro study of the proliferative response to extracellular ATP and adenosine

Unlike in higher vertebrates, in fish it is not known whether the nerve supply of the testis can influence testicular functions or not. In addition to neurotransmitters, nerve terminals may release ATP and adenosine in the extracellular medium. On the assumption that these molecules might be released by fibers innervating the teleost testis, it is possible that they participate in the control of testicular function and, maybe, in the control of spermatogonia (Go) proliferation. This study addresses this issue. We have investigated the ability for extracellular ATP and adenosine to influence the in vitro incorporation, either basal or GTH-, IGF-I- and suramin-stimulated, of 3H-thymidine (3H-Tdr) by trout Go. Mixed suspensions of somatic and germ cells prepared from testes, which were immature or spermatogenetic, were cultured usually for 4.5 days in the presence or not of the tested molecules; 3H-Tdr was added during the last day in culture. In our cell culture conditions, 25 to 250 microM adenosine, ATP, ADP, and AMP stimulated the 3H-Tdr incorporation by Go from prespermatogenetic testes and from testes starting spermatogenesis, in a dose-dependent way. The effect of these molecules decreased when the testes were more advanced in spermatogenesis and it became inhibiting when the testes were in mid-spermatogenesis. Five'-N-ethylcarboxamidoadenosine (NECA) was as potent as adenosine in stimulating or inhibiting 3H-Tdr incorporation, while R-N6-(2-phenylisopropyl)adenosine (R-PIA) always had a marked inhibiting effect. Adenosine 5'-O-(3-thiotriphosphate) (ATPgammaS; 25-200 microM), a non-hydrolysable analogue of ATP, which had no effect on Go from prespermatogenetic testes (collected October-February) and from testes in advanced spermatogenesis, stimulated 3H-Tdr incorporation by Go from testes at the beginning of spermatogenesis very efficiently. The order of potency of the different ATP analogues was as follows: ATPgammaS > ATP congruent with alpha,beta-methylene-ATP > UTP > 2-methylthio-ATP. These data suggest that A2 adenosine receptors and P2 receptors would be present on unidentified testicular cells. The stimulating effect of adenosine/ATP was additive with that of either GTH-I or IGF-I or suramin when the cells were from testes at the beginning of spermatogenesis, but adenosine suppressed their effect when the cells were from testes in mid-spermatogenesis. In conclusion, our results suggest that in the trout extracellular adenosine and ATP are able to influence the in vitro proliferation of Go, and are potential candidates for mediating the possible influence of the nervous system on the induction, speeding up, then slowing down of spermatogenesis.

Spermatogonia of rainbow trout: II. in vitro study of the influence of pituitary hormones, growth factors and steroids on mitotic activity

At the present time, in spite of recent advances, knowledge about the factors regulating germ cell proliferation in the teleost testis is limited. This study was designed to investigate, in vitro, the ability of various hormones, growth factors, and steroids to influence the proliferation of trout spermatogonia (Go) present in mixed cultures of somatic and germ cells prepared from testes, either prespermatogenetic or spermatogenetic. The tested molecules were usually present for the duration of culture (4.5 days) and 3H-thymidine (3H-Tdr) for the last day in culture. In our cell culture conditions, homologous gonadotropin I (tGTH-I) and growth hormone (tGH) moderately stimulated 3H-Tdr incorporation by Go, with ED50 equal to 5.5 +/- 3.0 and 1.8 +/- 0.4 ng/ml respectively. Insulin growth factor I (rhIGF-I) and fibroblast growth factor (rhFGF-2) stimulated 3H-Tdr incorporation by Go from spermatogenetic testes only, with ED50 equal to 16.2 +/- 9.3 and 2.4 +/- 0.3 ng/ml respectively. The effects of the most efficient concentrations of rhIGF-I combined with those of either tGTH-I or tGH were additive. Seventy to one hundred microM suramin stimulated 3H-Tdr incorporation by Go from testes at all maturation stages and this effect was additive with that of tGTH-I. We assume that this effect of suramin could result from the inhibition of an unidentified antimitogenic factor. No effect was observed with homologous prolactin, human epidermal growth factor, activin A and B, transforming growth factor-beta1, testosterone, 11-ketotestosterone, 17beta-estradiol, pregnenolone, 11beta-hydroxyprogesterone, and 22-hydroxycholesterol. In conclusion, our in vitro results suggest that GTH-I, GH, IGF-I, and FGF-2, are potent in situ modulators of the proliferative activity of trout Go at the time of induction, speeding up, then slowing down spermatogenesis, through direct or indirect additive and/or antagonistic influences.

Synthesis and regulation of 17α-hydroxy-20β-dihydroprogesterone in immature males of Oncorhynchus mykiss

Three experimental approaches were chosen to study the question if the progestin 17α-hydroxy-20β-dihydroprogesterone (17α20βOHP) is synthesised in testes of young Oncorhynchus mykiss, in which the absence of spermatozoa was verified histologically: first, in order to detect 20β-hydroxysteroid dehydrogenase activity (20βHSD), testes homogenates were incubated with (3)H-labeled 17αOHP.Metabolites were analysed by TLC, HPLC, and repeated crystallization to constant isotope ratios. One of the metabolites was identified as 17α20βOHP-(3)H, indicating that already immature testes contain 20βHSD activity and are able to produce 20β-reduced steroids. Second, 17α20βOHP was quantified by radioimmunoassay in incubates of testes fragments. The sensitivity of the gonads to gonadotropin II (GtH II) became evident when comparing incubations in the absence and presence of GtH II. Third, plasma levels of 17α20βOHP were significantly higher in animals injected with partially purified salmon gonadotropin, compared to controls. Thus, for the first time, it could be shown that 20βHSD is present in testicular cells other than spermatozoa. Furthermore, 17α20βOHP is indeed secreted at a very early stage of testicular development; 17α20βOHP secretion is also responsive to GtH II. Future studies will have to show if the functions of this progestin include the stimulation of spermatogenesis.

Subcellular fractionation of rainbow trout gonads with emphasis on microsomal enzymes involved in steroid metabolism

Rainbow trout gonads were subfractionated by differential centrifugation with emphasis on obtaining preparations suitable for the study of steroid-metabolizing enzymes. A fractionation scheme was evaluated for the mature testis and for 3 ovarian developmental stages. The distribution of cell organelles among the fractions was determined using enzyme-markers and electron microscopy. The fractionation scheme was found to be suitable for separating mitochondria and microsomes which were recovered at similar yields to those that had been reported for other extraheptic fish tissues. Fractionation of the mature ovary was fraught with problems probably because a large yolk protein cytosole fraction interfered with the recovery of microsomes. However, no difference in the specific activity of microsomal NADPH-cytochrome c-reductase between the various organ preparations was evident. The testis microsomes contained detectable amounts of cytochrome P450, whereas its content in the various ovary microsomes was too low to be detected. Progesterone 17 alpha-hydroxylase was detected in microsomes from testes and early developing ovaries, and microsomal aromatase activity was present in microsomes from early developing, mature and postovulatory ovaries. Furthermore, the testis microsomes contained a highly active UDP glucuronosyltransferase with testosterone used as a substrate.

Biotechnology and aquaculture: The role of cell cultures

Cell culturing complements recombinant DNA technology in the application of biotechnology to aquaculture. Cell cultures can be prepared from the three main groups of multicellular organisms in aquaculture: fish, shellfish, and seaweeds. These cultures can contribute indirectly to the successful farming of these organisms by providing basic insights into how their growth, reproduction, and health can be understood and manipulated. Finally, they can be a direct source of diverse biochemical products for use in aquaculture, medicine and the food industry.

Trout steroidogenic testicular cells in primary culture. II. Steroidogenic activity of interstitial cells, Sertoli cells, and spermatozoa

Somatic cells (interstitial cells and Sertoli cells) were prepared either as single cells or in clusters, from spermatogenic and mature trout testes, according to Loir (1988), and cultured for 10-14 days. Sertoli cells are 3 beta-HSD negative when prepared from testes resuming spermatogenesis and from mature testes, but they are 3 beta-HSD positive in spermatogenic testes. Progesterone, 17 alpha-hydroxyprogesterone (17 alpha-OH-P), and free androgens are secreted by interstitial cells, 11-ketotestosterone (11KT) being the predominating steroid produced immediately after seeding. These cells also produce high levels of glucuronated androgens. At least in mature spermiating testes they do not secrete estradiol. After isolation, interstitial cells would lose most of their ability to secrete 17 alpha-hydroxy,20 beta-dihydroprogesterone (17 alpha 20 beta-OH-P) but they would recover it later. Testicular spermatozoa, which convert 17 alpha-OH-P independently of s-GtH, constitute a second source of this progestagen. In addition, our results suggest that Sertoli cells could be able to secrete 17 alpha-OH-P and also progesterone. A possible participation of the intralobular production of the former progestagen to the local regulation of germ cell maturation is evoked.