Excretion of free and conjugated steroids in rainbow trout (Oncorhynchus mykiss): evidence for branchial excretion of the maturation-inducing steroid, 17,20 beta-dihydroxy-4-pregnen-3-one

The role of sex ratio on spawning performance and on the free and conjugated sex steroids released into the water by common dentex (Dentex dentex) broodstock

This paper reports the results of an experiment to determine whether sex ratio has any effect on the spawning efficiency of common dentex, Dentex dentex, broodstock. The paper also reports preliminary data on diurnal changes in water concentrations of steroids (measured on two separate occasions) in the same groups of fish. These latter observations were made to determine whether, using a non-invasive procedure, it was possible to relate hormonal changes in the fish to the "success of spawning." Mature fish were placed in broodstock tanks at three different sex ratios (Group A, 4 female:1 male; Group B, 1 female:1 male; and Group C, 1 female:4 male) and regularly monitored for egg production. At 18 days after the start of spawning, water samples were removed from all three tanks at 130 min intervals over a period of 24 h. At the end of spawning, water samples were removed at 4 h intervals. Free and conjugated steroids were extracted from the water and measured by radioimmunoassay. The highest number of eggs released, percentage of viable eggs, number of spawnings, spawning index, and relative fecundity were observed in Group B (1 female:1 male). The sex steroids testosterone (T), 11-ketotestosterone (11-KT), 17,20beta-P, and 17,20beta, 21-trihydroxy-pregn-4-en-3-one could be readily detected in water from all tanks. Concentrations of the conjugated forms (sulphate and glucuronide) were higher than those of the free form--with the exception of sulphated T and 11-KT. The concentrations of glucuronidated 17,20beta-P, sulphated 17,20beta-P, and free T appeared to be associated with the number of females in the tank and glucuronidated 11-KT concentrations with the number of males. In the first set of water samples (taken during the spawning period) there was also evidence for a cycle in steroid release with an acrophase during the afternoon and early evening, a few hours before the actual act of spawning. We were not able to show any association between steroid concentrations and success of spawning. However, since the data were derived from a "snapshot" of just a single day in what was a prolonged spawning period, this was perhaps not surprising. The results from the present study will help us to design experiments that are more able to answer this question.

Male sea lampreys, Petromyzon marinus L., excrete a sex pheromone from gill epithelia

During the period when they are producing sperm, male sea lampreys (Petromyzon marinus L.) release a sex pheromone 7alpha, 12alpha, 24-trihydroxy-5alpha-cholan-3-one-24-sulfate (3 keto-petromyzonol sulfate, 3ketoPZS) that induces search and preference behaviors in ovulating females. In this study, we conducted a series of experiments to demonstrate that release of this pheromone into water takes place exclusively through the gills. In a behavioral maze, water conditioned with the anterior region of spermiating males induced an increase of search and preference behaviors in ovulating females. Similar behavior was not elicited by water conditioned by the posterior region. The anterior region washings and whole-body washings from spermiating males also elicited large and virtually identical electro-olfactogram responses from female sea lampreys, while the posterior washings produced negligible responses. Further, mass spectrometry and immunoassay confirmed that virtually all the 3ketoPZS released into water was through the gills. Immunocytochemistry revealed some gill epithelial cells and hepatocytes from spermiating males contained dense immunoreactive 3ketoPZS, but not those from prespermiating males. These results demonstrate that 3ketoPZS is released through the gill epithelia and suggest that this pheromone or its precursor may be produced in the liver.

Intestinal and hepatic microsomal metabolism of testosterone and progesterone by a 3 alpha-hydroxysteroid dehydrogenase to the 3 alpha-hydroxy derivatives in the channel catfish, Ictalurus punctatus

Intestinal or hepatic microsomes from channel catfish converted [4-14C]-testosterone to three major metabolites: 6 beta-hydroxytestosterone, androstenedione and a third metabolite. Formation of the unknown metabolite required NADPH as cofactor. When incubated with 200 microM testosterone, the rate of formation of the unknown metabolite was 265+/-158 pmol/(min mg) protein (mean+/-S.D.) in microsomes from the proximal intestine, 515+/-93 pmol/(min mg) protein in distal intestine and 226+/-42 pmol/(min mg) protein in hepatic microsomes. Comparison of the chromatographic and spectral properties of the unknown metabolite with those of authentic testosterone derivatives showed that this metabolite corresponded to 4-androstene-3 alpha,17 beta-diol. No 3 alpha-reduced metabolite was formed in incubations of testosterone with catfish intestinal cytosol. Testosterone was reduced to 5 alpha-dihydrotestosterone primarily in the cytosolic fraction and not in microsomes. Incubation of progesterone with intestinal microsomes resulted in the formation of a metabolite with properties similar to that of the 3 alpha-reduced testosterone, and this metabolite was identified by co-chromatography with authentic standard as 3 alpha-reduced progesterone. Thus, 3 alpha-hydroxysteroid dehydrogenase is an important pathway in intestinal microsomes of the channel catfish.

Ejaculate of sneaker males is pheromonally inconspicuous in the black goby, Gobius niger (Teleostei, Gobiidae)

The black goby, Gobius niger, shows alternative male mating tactics, i.e., parental and sneaker males. Males release a sexual pheromone that attracts females and stimulates aggressive displays in males. This pheromone is produced by the mesorchial gland, a structure well developed in parental males but markedly undeveloped in sneakers. We measured the behavioral response of parental males to the ejaculates of males performing different reproductive tactics. Parental males reacted to the ejaculate of other parental males, with stereotypic aggressive behaviors, but not to the ejaculate of sneakers; consequently sneaker male ejaculate appears to be pheromonally inconspicuous.

Cloning of zebrafish ovarian carbonyl reductase-like 20 beta-hydroxysteroid dehydrogenase and characterization of its spatial and temporal expression

20 beta-Hydroxysteroid dehydrogenase (20 beta-HSD) is a crucial enzyme that converts 17 alpha-hydroxyprogesterone to 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (DHP), which triggers oocyte maturation in most teleost fish. A full-length cDNA for a carbonyl reductase-like 20 beta-HSD (CR/20 beta-HSD) has been cloned from the zebrafish ovary. Although the zebrafish CR/20 beta-HSD is expressed in all of the tissues tested, it is predominantly expressed in the ovary, testis, kidney, and gill. In the ovary, the enzyme was shown to be expressed in the follicle cells and its expression appeared to be constitutive. No significant difference was noticed in the level of CR/20 beta-HSD expression among follicles of different stages. Furthermore, analysis of the ovarian samples taken at different times before spawning showed no significant change of the enzyme expression. In agreement with these results, treatment of the cultured zebrafish ovarian follicle cells with gonadotropin and activin had little effect on the expression of the enzyme. Taken together, these results point to the possibility that the gonadotropin-induced DHP production and final oocyte maturation in the zebrafish may not involve significant change of CR/20 beta-HSD expression as evidenced in the salmonids, or that there might be other isoforms of 20 beta-HSD whose expression is tightly controlled by endocrine and paracrine factors.

Bile Acid secreted by male sea lamprey that acts as a sex pheromone

We show that reproductively mature male sea lampreys release a bile acid that acts as a potent sex pheromone, inducing preference and searching behavior in ovulated female lampreys. The secreted bile acid 7alpha,12alpha,24-trihydroxy-5alpha-cholan-3-one 24-sulfate was released in much higher amounts relative to known vertebrate steroid pheromones and may be secreted through the gills. Hence, the male of this fish species signals both its reproductive status and location to females by secreting a pheromone that can act over long distances.

Putative steroidal pheromones in the round goby, Neogobius melanostomus: olfactory and behavioral responses

To identify potential hormonal pheromones of the round goby (Neogobius melanostomus), a species recently introduced to the Great Lakes, we used electro-olfactogram (EOG) recording to examine olfactory responsiveness to more than 100 steroids and prostaglandins. Neogobius detected free and conjugated 18-, 19- and 21-carbon steroids, but did not detect prostaglandins. EOG cross-adaptation, used to determine if Neogobius can discriminate the detected compounds at the sensory level, suggested that the detected steroids act on four classes of olfactory receptor mechanisms named (according to the most potent ligand for each): estrone, 17 beta-estradiol-3 beta-glucuronide, etiocholanolone, and dehydroepiandrosterone-3-sulfate. Although none of the detected steroids induced reproductive behaviors, exposure to steroids from three of the four receptor classes (estrone, 17 beta-estradiol-3 beta-glucuronide, or etiocholanolone) increased ventilation rate in males, whereas only etiocholanolone increased ventilation rate in females. Using the ventilation increase as a behavioral bioassay of steroid detection, behavioral cross-adaptation studies in males demonstrated that steroids discriminated at the sensory level are also discriminated behaviorally. These findings suggest the round goby may use steroids as putative pheromones.

Circulating C-21 steroids in relation to reproductive condition of a viviparous marine teleost, Sebastes rastrelliger (grass rockfish)

Plasma concentrations of free, glucuronidated, and sulfated steroids were measured in grass rockfish (Sebastes rastrelliger) at identified stages of ovarian development and pregnancy using radioimmunoassays validated for the detection of individual steroids or compounds with a particular configuration. Changes in reproductive status were most clearly reflected in concentrations of free C-21 steroids. Previtellogenic, vitellogenic, and postspawn fish exhibited uniformly low concentrations of circulating C-21 steroids while pregnant fish showed a pronounced and significant increase in a series of free 17,20beta-dihydroxylated steroids together with 17,20alpha-P. Among individual steroids, the compound exhibiting the greatest fluctuation in relation to reproductive condition was 17,20beta-P-5beta, which during pregnancy showed a 22-fold increase from basal concentrations. Smaller relative increases in association with pregnancy were also seen in 17, 20beta-P, 17,20beta,21-P, and 17,20alpha-P (3.5-, 3.5-, and 5.5-fold increases, respectively). Fish in the final stages of pregnancy or which had recently spawned exhibited uniformly low concentrations of the C-21 steroids, indicating a drop in circulating amounts of these compounds around the time of parturition. The hormone profiles established during the annual reproductive cycle of the grass rockfish suggest that C-21 steroids may contribute to the endocrine mechanisms which regulate viviparity in this highly fecund marine teleost. The C-21 steroids characterized in this study may provide appropriate reference compounds in the future evaluation of this concept.