In vitro studies on steroid metabolism by gonadal tissues from ambisexual teleosts. II. Conversion of [14C]androstenedione by the heterologous gonadal tissues of the protandric sea bream Pagellus acarne (Risso)

Steroidogenesis by testis and accessory glands of the Lusitanian toadfish, Halobatrachus didactylus, during reproductive season

In teleost fish sex steroids are essential for gonadal function and have marked effects in reproductive and agonistic behavior and in the expression of secondary sexual characteristics. The Lusitanian toadfish, Halobatrachus didactylus, has two male morphotypes: type I males are territorial nest-holders and have large accessory glands while type II males are smaller, have a relatively large testis and small accessory glands. In the present study, the steroidogenic activity of the testis and accessory testicular glands of the Lusitanian toadfish were examined in vitro as well as their presence in urine. The testis of type I males produced 11-ketotestosterone (11KT) and 11β-hydroxy-4-androstene-3,17-dione (11βA) from tritiated 17-hydroxyprogesterone, while those of type II males produced testosterone (T) and 11β,17β-dihydroxy-4-andosten-3-one (11βT), but not 11KT. Additionally, the testis and accessory glands of both morphs produced mostly 5β,3α-reduced and 17,20α-hydroxylated metabolites. Type I, but not of type II, males synthesised 5β-reduced androgens in their accessory glands. The presence of 11βA exclusively in the urine of type I males during reproductive season suggests an association with maintenance of secondary sexual characteristics and behavior in this morph. The urine of both types of males contained two 5α-androstane and 5β-pregnane glucuronides. Among the latter steroids, those that are 17,21-dihydroxylated are potentially metabolites from cortisol and were found only in type I males during the spawning season. The diversity of metabolites produced by the testis and accessory glands and the presence of some in urine is suggestive of a potential role in chemical communication and reproductive behavior.

Gonadal steroidogenesis in response to estradiol-17beta administration in the sea bream (Sparus aurata L.)

The sea bream (Sparus aurata) is a protandrous hermaphrodite teleost fish in which estrogen administration induces testicular regression without influencing ovarian development. To analyze the changes in steroidogenesis of fish treated with two levels of estrogen (2 and 10 mg. kg(-1)) and untreated control fish, fragments of gonads were incubated with tritiated 17-hydroxyprogesterone and the metabolites identified. The ability to extract radioactivity decreased with incubation time and was lower in gonads containing a larger proportion of ovarian tissue. The difference in steroidogenic capacity between control and estrogen-treated groups was generally quantitative rather than qualitative and paralleled the observed histological changes. The same metabolites were identified in all three groups, but estrogen treatment caused a marked inhibition of 5beta-reduction, 3alpha-reduction, side-chain cleavage, and 11beta-hydroxylation. The main androgens identified were 11beta-hydroxy-4-androstene-3,17-dione and 3alpha-hydroxy-5beta-androstane-3,17-dione, and the synthesis of both steroids was inhibited by estrogen treatment. Of the more polar pregnanes, 5beta-pregnane-3alpha,17,20alpha-triol and 5beta-pregnane-3alpha,17,20beta-triol were detected in significant amounts, but only the latter appeared to be associated with development of the testis (in the untreated fish). A feature of sea bream gonadal steroidogenesis less common in other teleosts was the presence of 6alpha- and 6beta-hydroxylation.

The effect of estrogen on the gonads and on in vitro conversion of androstenedione to testosterone, 11-ketotestosterone, and estradiol-17beta in Sparus aurata (Teleostei, Sparidae)

The effects of estrogen on gonad morphology and steroidogenesis of sea bream, Sparus aurata, a protandrous hermaphrodite teleost, were investigated. Fish were treated in winter/spring for different periods with 17alpha-ethynylestradiol (ethE(2); experiment 1) and in summer with two doses of estradiol-17beta (E(2); experiment 2). Estrogen was more effective in summer. Its main effect on the gonad was inhibition of testicular growth and of male germ cell development beyond the spermatogonia stage, including mitosis. The effect of estrogen on ovarian development was slight and only apparent at the end of experiment 2 in the higher dose group. Gonadal fragments were incubated at different times during treatment with androstenedione and the output of testosterone (T), estradiol (E(2)), and 11-ketotestosterone (11KT) was measured by radioimmunoassay. T and E(2) production was inversely correlated with the proportion of testicular tissue (and positively with ovarian tissue) in the gonad in experiment 2. However, the production of 11KT was not correlated with any type of tissue, possibly because of further metabolism. Inhibition of testicular development by estrogen was also associated with higher output of steroid conjugates.

Plasticity of gonadal development and protandry in fishes

Sexual differentiation in eutherian mammals follows a simple governing paradigm: development proceeds in a female direction unless a masculinizing mechanism intervenes. Sexual development in fishes is much more plastic than in mammals. It permits the intervention of environmental factors and follows several different types of sequences that produce successive hermaphrodites and alternative pathways for the development of the same final sex. In spite of this plasticity, the primacy of female development is suggested by the initial ovarian phase in the development of gonads of both sexes in some gonochoristic fishes and by protogynous sex change. One barrier to the application of this principle to fishes generally is the existence of protandric hermaphrodites. Recent evidence suggests a reinterpretation of gonadal differentiation in a protandric anemonefish and a protandric sparid. In both cases, testicular development is both preceded and followed by ovarian development. These patterns are interpreted to mean that female development is primary and that male development is a temporary phase initiated by a masculinizing mechanism and terminated by its cessation.

Histology, ultrastructure, and in vitro steroidogenesis of the testes of two male phenotypes of the protogynous fish, Thalassoma duperrey (Labridae)

Species with multiple male reproductive phenotypes may serve as model systems to study the relationship between form and function in reproduction. Large and small males of the protogynous wrasse, Thalassoma duperrey differ in reproductive behavior, gonad morphology, and gonadal steroid production. Initial-phase (IP) males are small males that spawn in groups. They have large testes with high sperm production. Terminal-phase (TP) males are large, defend temporary spawning territories, and spawn individually with females. TP males are derived from either IP males or from sex-changed females. Regardless of origin, TP males have much smaller testes than do IP males, but steroid-producing Leydig cells in the gonads of TP males appear more numerous and better developed. Testes of TP males produce more testosterone (T) and especially 11-ketotestosterone (11-KT) in vitro than do testes of IP males, and the production is more responsive to salmon gonadotropin. 11-KT was the major metabolite produced by incubating the gonads of TP males with 14C-labeled steroid precursors. In vitro 11-KT production was correlated with plasma levels of 11-KT in TP males and these levels were significantly higher than those of IP males. The in vitro conversion of 17 alpha-hydroxyprogesterone to 17 alpha, 20 beta-progestogen (17 alpha, 20 beta-P) for both types of males was similar, and was highest in winter when spawning occurred every day. Basal production of 17 alpha, 20 beta-P was similar in IP and TP male testes, and was enhanced by gonadotropin. The enzyme 20 beta-hydroxysteroid dehydrogenase, responsible for the conversion of 17 alpha-hydroxyprogesterone to 17 alpha, 20 beta-P resided in the sperm. These results indicate a function of 17 alpha, 20 beta-P in male reproductive function, probably spermiation, and a relationship of Leydig cell development and high levels of 11-KT production to the terminal male phenotype, perhaps reproductive or aggressive behavior, rather than to male gametogenesis per se.

The biosynthesis of 11-ketotestosterone by the testis of the Siamese fighting fish Betta splendens Regan (Anabantoidei, Belontiidae)

Testicular tissues of the Siamese fighting fish were incubated with [14C]pregnenolone for 10, 20, 30, 50, 80, and 120 min, and with [14C]progesterone, [14C]11 beta-hydroxyandrostenedione, [14C]11 beta-hydroxytestosterone, and [14C]androstenetrione for 120 min. 11-Ketotestosterone was the main metabolite in all 120-min incubations. No 11-oxygenated C21 steroids were found as metabolites of either pregnenolone or progesterone. The biosynthesis of 11-ketotestosterone proceeded through both the delta 5- and the delta 4- pathways as judged from the shape of the yield-time curves of the metabolites of pregnenolone. 11-Ketotestosterone formation from 11-oxygenated precursors increased in the order 11 beta-hydroxytestosterone less than 11 beta-hydroxyandrostenedione less than androstenetrione.