Impaired spermatogenesis in the Japanese eel, Anguilla japonica: Possibility of the existence of factors that regulate entry of germ cells into meiosis

In the cultivated male Japanese eel, spermatogonia are the only germ cells present in the testis. Weekly injections of human chorionic gonadotropin (HCG) can induce complete spermatogenesis from proliferation of spermatogonia to spermiogenesis. In some cases, however, HCG injection fails to induce complete spermatogenesis. Testicular morphological observations revealed that HCG-injected eels could be classified into three types based on their testicular conditions. Type 1 eels had a well-developed testis and the milt could be acquired by hand-stripping. In type 2 eels, spermatogenesis was also induced by HCG injection, but testicular size was remarkably smaller than that of type 1 eels, and the milt could not be hand-stripped. At the end of the experiment, type 2 fish had only spermatogonia and a small amount of spermatozoa, but no spermatocytes or spermatids, in their testis. Type 3 eels had thready testis, which did not develop any germ cells during the experimental period. These results suggest that, despite elevations of plasma 11–ketotestosterone levels, HCG injections were not successful in inducing the completion of spermatogenesis in type 2 and type 3 eels. In most spermatogonia of type 2 eels, meiosis was not induced by HCG injections. Furthermore, only few mitotic divisions had occurred as evidenced by the presence of 2³ to 2⁶ late type B spermatogonia in most cysts. This suggests that spermatogonial stem cells undergo four or five, and occasionally six, mitotic divisions before the interruption of spermatogenesis in type 2 eels. It is proposed that those numbers of mitotic divisions are related to a mediator that regulates entry of spermatogonia of the Japanese eel into meiosis.     

Effects of HCG or gonadoreline on seminal parameters and plasma testosterone levels in young male rabbits

The effect of successive HCG or Gonadoreline injections on some reproductive parameters in 21 young male rabbits, aged from 4 to 4.5 months, has been studied. Animals were randomly allocated in three groups of seven to receive weekly (on each Monday) i.m. injections of 20 mg Gonadoreline, 50 IU HCG, or 0.5 ml Saline solution, respectively. The ejaculate from each male was collected and analysed twice a week (Tuesday and Friday). Higher sperm volumes were observed on the first week after Gonadoreline administration compared to the other groups (p < 0.05), and lower values during the second week in the Control group vs. Gonadoreline group (p < 0.05). Sperm volume increases after the 3rd week in Control animals (p < 0.05). When considering the global period studied, mean sperm volumes achieved after Gonadoreline treatment were higher than in HCG or Control group. Despite the random distribution of the animals to each treatment, and although throughout the experiment more ejaculates were discarded in the Gonadoreline group, the final number of doses obtained per ejaculate was higher in this group followed by HCG treated animals. Globally, the mean sperm concentration of the Control group during the entire studied period was significatively lower compared to the other groups (p < 0.001). No sperm motility differences were detected among the groups (p < 0.1174). HCG injections caused a significative increase in plasma testosterone concentration during the first and second week (p < 0.001) and similar plasma levels were observed in all groups afterwards. No direct plasma testosterone increasing levels owed to Gonadoreline injections were detected, probably due to the frequency of blood sampling (once a week).     

Role of testosterone levels and of hypophysis in the HCG-induced modifications of the 7 alpha-hydroxylation and 5 alpha-reduction processes in incubated rat testes

The role of a direct or a hypophysis-mediated influence of increased testosterone levels in the effects of a long-term high-dose HCG administration (10 IU/day) upon the 7 alpha-hydroxylation and 5 alpha-reduction activities of incubated testes of mature rats was investigated. Administration of high doses of HCG to hypophysectomized rats resulted in the same metabolic changes as in normal rats, namely, a large decrease in the 7 alpha-hydroxylation and an increase in the 5 alpha-reduction processes. Administration of testosterone-propionate (0.2 mg and 20 mg/day) for several days to hypophysectomized rats and to normal rats receiving and substitutive dose of 1 IU HCG/day, did not modify the testicular metabolization pattern. These findings indicate that the decrease in testicular 7 alpha-hydroxylation activity induced by long-term administration of high doses of HCG is probably not mediated by the hypophysis nor by the extracellular testosterone levels.     

Gonad differentiation and body growth in Anguilla anguilla L.

Using histological sections, the gonads of samples of yellow and silver eels of two populations were examined. The populations were previously analysed for growth and sex ratio. The histological structures observed are similar to those described in previous publications for the European eel, Anguilla anguilla and to those indicated for the Pacific eel, A. japonica . Well differentiated gonads are present in the silver eels. In the yellow eels, ranging in age from 0 + to 2 + years and from a length of 20 cm to that at which they become silver, undif-ferentiated and both sex gonads are found. Histological evidence is presented which suggests that the ovary, found even in young and small eels, is completely differentiated at a very early stage. The testis-like gonad of the yellow eel is a more primitive, and possibly reversible, gonad which differentiates completely at the beginning of sexual maturation and the change to the silver phase.     

Effect of gonadotrophins and testosterone on the seminiferous tubules of the immature rat.

The actions of HCG and PMSG for different periods and of testosterone of the immature rat testis were studied. Short-term administration of HCG (1-3 days) induced an early meiotic and postmeiotic stimulatory effect but a decrease in spermatogonial numbers. Administration of HCG for longer periods (10 days) caused a reduction in numbers of all cell types. Treatment with HCG + PMSG reduced the amount of inhibition, while PMSG alone resulted in histological and humoral signs of stimulation of the interstitial tissue and the meiotic and postmeiotic stages; the numbers of spermatogonia were not affected. Testosterone caused stimulation of the meiotic and postmeiotic stages and a reduced number of spermatogonia. It is concluded that while PMSG directly stimulates spermatogonia, HCG acts through testosterone secretion at the meiotic and postmeiotic stages. The early inhibitory effects of HCG and testosterone on spermatogonial numbers could be ascribed to the inhibition of endogenous FSH by androgens.     

Development and early differentiation of gonad in the european eel (Anguilla anguilla [L.], Anguilliformes,Teleostei): A cytological and ultrastructural study

The structure of the gonad of the European eel (Anguilla anguilla [L.]), an “undifferentiated” gonochoristic teleost, was investigated by transmission electron microscopy from 6–8 cm elvers to 22 cm yellow eels with juvenile hermaphroditic gonads. The pear-shaped gonads of 6–8 cm elvers assume, in 12–15 cm eels, a lamellar shape and enlarge by migration of germ cells, which we refer to as primary primordial germ cells. In the gonads of ∼ 16 cm eels, the primary primordial germ cells multiply, giving rise to clusters of germ cells that have ultrastructural characteristics of the primary primordial germ cells but show giant mitochondria, enlarged Golgi complexes, and round bodies not limited by membranes. We refer to these as secondary primordial germ cells. In 16–18 cm eels, syncytial clones of oogonia interconnected by cytoplasmic bridges are also observed. In 18–22-cm-long eels, the gonads contain primordial germ cells, oogonial clones, early oocyte cysts, single oocytes in early growth stages, and primary spermatogonia. Such germ cells are present in the same cross section where they are either intermingled or are in areas of predominantly female germ cells close to areas with predominantly male germ cells. These gonads are juvenile hermaphroditic and should be considered ambisexual because in larger eels they differentiate either into an ovary or into a testis. Somatic cells always envelop the germ cells following their migration into the gonad. These somatic cells first show similar ultrastructural features and then differentiate either into early Sertoli cells investing spermatogonia, or into early follicular (granulosa) cells investing the early previtellogenic oocytes. In eels ∼ 14 cm long, primitive steroid-producing cells also migrate into the gonad. In the ambisexual gonad they differentiate either into immature Leydig cells in the male areas, or into early special cells of the theca in the female areas. Nerve fibers are joined to the steroid-producing cells. Gonad development and differentiation are also associated with structural changes of the connective tissue characterized by the progressive appearance and deposition of collagen fibrils first in the mesogonadium, then in the gonad vascular region, and then in the germinal region. The collagen-rich areas are massive in the male areas and reduced in the female ones. J. Morphol. 231:195–216, 1997. © 1997 Wiley-Liss, Inc.     

Histological study of the development and sex differentiation of the gonad in the European eel

The histological structure of the gonads was studied in yellow eels sampled from a coastal lagoon and from stocks reared in an aquaculture plant showing different sex ratios. Gonad development related to body size rather than to age and underwent an intermediate stage characterized by a structure of an early testis but containing oogonia and oocytes. This gonad was called the Syrski organ and the stage juvenile ambisexual. Ovaries were found in eels from 22–30 cm in length, possibly derived from undifferentiated gonads or from Syrski organs. Fully differentiated testes were found in eels >35 cm, derived from Syrski organs. These observations support the results of previous research. From elvers and in eels up to 15–16 cm in length, growth of the gonadal primordium is due to primordial germ cell migration. In eels > 15 cm multiplication of primordial cells begins. Oogonial clones were found in eels > 18 cm in length, whilespermatogonium B clones were observed in eels >30 cm in length. The dynamics of sex differentiation was different among stocks with different ultimate sex ratios: ovaries were found in shorter eels in stocks with a prevalence of females, in longer eels in stocks with a prevalence of males. This result supports the hypothesis of a metagametic (environmental) sex determination. The somatic cells in contact with germ cells and those in the interstitium appeared early during gonad development and preceded germ cell differentiation. This suggests that somatic cells are the targets of the environmental factors influencing sex differentiation.     

未产卵雌性黄鳝的性转变

为探讨产卵是否为雌性黄鳝(Monopterus albus Zuiew)性转变的必经过程,研究分析了实验室内从受精卵或幼苗开始养殖至不同时间段的黄鳝性腺组织学状况,采用性腺活检技术跟踪了34月龄雌性黄鳝性腺发育变化,并以免疫组织化学方法探讨了黄鳝不同发育状态性腺中增殖细胞核抗原(PCNA)的分布.在养殖过程中,实验黄鳝...     

Long-term effect of HCG on plasma testosterone in bulls.

The spontaneous diurnal variation of peripheral plasma testosterone concentrations in four bulls was established and then the long-term effect of a single intravenous or intramuscular injection of HCG on testosterone levels was studied. Intravenous and intramuscular HCG injections produced, within 1/2 hr and 3 hr, respectively, a rapid rise of testosterone to levels equivalent to the highest values seen in the diurnal pattern. A second increase of up to x2 to x3 the highest values of the diurnal cycle was observed 2 days after the injection of HCG, and the testosterone level remained high for at least 3 to 4 days after plasma levels of HCG were no longer detectable. The pattern of diurnal variation after HCG revealed an attenuation of the extensive spontaneous variation and high levels with only slight fluctuations were maintained.     

Embryonic sex hormones in birds

Hormone activity of embryonic gonads in birds was demonstrated by grafting and culture experiments. Anti-Müllerian hormone responsible for the regression of the Müllerian ducts in the male is most probably a glycoprotein. Whether the testis also secretes testosterone has long been disputed, but most arguments are against this possibility. From early stages of development, the ovary secretes estrome and estradiol. However, it could not be demonstrated unambiguously whether estrogen is identical with the sex inducing substance in the female. The hypophysis seems to control ovarian estrogen secretion at 10-13 days of incubation in the chick embryo.     

Karyological and gonadal sex of eels(Anguilla anguilla) from the German Bight and the lower River Elbe

Yellow eels(Anguilla anguilla) taken during summer from random commercial trapnet samples in the littoral area of Helgoland (n=116) and from a freshwater area of the River Elbe near Hamburg (n=109) were examined with regard to their karyological (i.e. existence of female sex chromosomes) and gonadal sex. In 47 % and 21 % of the two samples, respectively, chromosomes were unidentifiable because of insufficient numbers of mitotic plates. All eels from Helgoland, except one phenotypically undetermined fish, exhibited female gonads: 48 had female sex chromosomes and 13 were karyologically males. As found previously in the River Elbe, eels with male gonads predominated (n=55); 25 were undifferentiated. Of the gonadal males 26 were karyological males and 16 karyological females; the rest could not be identified by chromosome patterns. In contrast, all but one of the Elbe eels with female gonads (n=28) had female sex chromosomes. Some aspects of the sex reversal documented in the eel are considered.     

Effects of oestradiol—enriched diet and of feeding with porcine testicular tissue on macroscopic gonadal sex in European eels

Oestradiol–enriched food (25 mg kg^-1 oestradiol) fed for 91 days to small eels (2 or 7 g) with undifferentiated gonads (UD) significantly favoured development of gonads with the macroscopic appearance of ovaries (♀-gonads) during the next 8 months. Fifty-four and 51% of control eels and 75 and 78% ofoestradiol-treated eels developed ♀-gonads. Minced porcine testicular tissue fed to 2-g eels for up to 371 days had effects similar to oestradiol-enriched food (68% with ♀-gonads), whereas feeding for only 91 days had no effect during the next 8 months. Oestradiol-enriched food was also fed to larger eels with already macroscopically differentiated gonads (30–70 g; 95% with ♀-gonads, 5% with ♀-gonads). After 27 days significantly more eels with a ♀-gonad or with a mixture of ovary-like and testis-like regions in the gonads (♂+♀-gonads) were found. After 96 days there were 44% with ♀-gonads, 40% with ♂+♀-gonads and 16% with ♀-gonads. Oestradiol thus had a feminizing effect, not only on morphologically undifferentiated gonads but also on morphologically differentiated ♀-gonads. The presence of sex steroid hormones or their precursors in porcine testicular tissue may also exert a feminizing influence. In all experiments the hormone-fed groups showed a tendency (not significant) towards increased growth rate. In small eels early rapid growth and differentiation of ♀-gonads were clearly correlated, both in hormone treated and in control eels. Otherwise no correlation was found between growth rate and gonadal sex.     

A unifying concept of chorionic gonadotrophin production in malignancy

Elevated blood levels of immunoreactive human chorionic gonadotrophin (HCG) have been reported in many patients with non-trophoblastic tumours, but also in various non-malignant conditions. Even normal tissues other than placenta have been shown to produce HCG, such as gonads, gastrointestinal tract, liver, and pituitary. Since HCG is produced, albeit at a low level, by a variety of normal tissues, there is no need to invoke the gene derepression theory to account for 'ectopic' HCG production. However, tumours associated with excess of biologically active HCG as evidenced by endocrinological abnormalities, such as precocious puberty or gynaecomastia, are very rare. We have reviewed the world literature and found 44 such tumours in the lung, adrenal gland, liver, gastrointestinal tract, and genitourinary tract (excluding the gonads). The analysis of their histological pattern shows that they typically contain syncytial giant cells or frankly choriocarcinomatous elements. In this respect they are like germ-cell tumours associated with excess HCG production. The precursor of the HCG-containing cells in 'somatic' tumours is unknown but their functional and morphological similarity to the trophoblast revives the old concept of pathophysiological correspondence between some malignant tumours and invasive trophoblast.     

Heme oxygenase-mediated endothelial dysfunction in DOCA-salt, but not in spontaneously hypertensive, rat arterioles

Vascular heme oxygenase (HO) metabolizes heme to form carbon monoxide. Carbon monoxide inhibits nitric oxide synthase and promotes endothelium-dependent vasoconstriction. We reported HO-1-mediated endothelial dysfunction in Dahl salt-sensitive hypertension. Previous studies suggested that salt-sensitive hypertensive rats, but not spontaneously hypertensive rats (SHR), display endothelial dysfunction. This study examines the hypothesis that HO-1-mediated arteriolar endothelial dysfunction develops in deoxycorticosterone acetate (DOCA)-salt hypertensive (DOCA) rats, but not in SHR. Uninephrectomized (isoflurane anesthesia) male Sprague-Dawley rats received DOCA injections and saline drinking solution for 4 wk. Rats subjected to sham surgery received vehicle injections and tap water. Blood pressure was elevated in DOCA rats and SHR compared with sham and Wistar-Kyoto (WKY) groups. Aortic HO-1 expression and blood carboxyhemoglobin levels were elevated in the DOCA group, but not in SHR. In isolated gracilis muscle arterioles, ACh caused concentration-related vasodilation in all groups, with attenuated maximum responses in DOCA, but not in SHR, arterioles. Acute pretreatment with an inhibitor of HO, chromium mesoporphyrin, restored ACh-induced responses in DOCA arterioles to sham levels. ACh responses remained the same in SHR and WKY arterioles after chromium mesoporphyrin treatment. These data show that HO-1 levels and activity are increased and arteriolar responses to ACh are decreased in DOCA rats, but not in SHR. Furthermore, in DOCA arterioles, an inhibitor of HO restores ACh-induced vasodilation to sham levels. These results suggest that elevated HO-1 levels and activity, not resulting from hypertension per se, contribute to endothelial dysfunction in DOCA rats.     

Histological changes in the gonad, skin, intestine and olfactory epithelium of artificially-matured male American eels, Anguilla rostrata (LeSueur)

Migratory (silver) male American eels were injected weekly for 5 weeks with human chorionic gonadotropin (hCG), salmon pituitary extract, hydrocortisone 21-hemisuccinate (cortisol), or saline to determine the effects of induced maturation on the histology of their gonads, skin, intestines and olfactory epithelia. Treatment with hCG induced full sexual maturity, salmon pituitary evoked only limited spermatogenesis, and neither hydrocortisone nor saline had any effect on the gonad. Eels injected with hCG and salmon pituitary experienced no changes in skin morphology, but the epidermal thickness of saline- and hydrocortisone-treated fish decreased. Intestinal morphology did not change in any of the treatment groups. Both the presumed sensory and non-sensory portions of the olfactory epithelium of hCG- and pituitary-treated males exhibited a decrease in thickness, structural degeneration, and non-significant reductions in mucous cell density. Some of these changes in maturing male eels are similar to those previously observed in maturing females but others are different; it appears likely that maturing Anguilla are sexually dimorphic and that these changes are adaptive and not artifacts of the hormone treatments.     

The role of the gonads and the hypophysis in the regulation of hydroxysteroid dehydrogenase activities in rat kidney.

With the exception of 3beta-hydroxy-steroid dehydrogenase all the hydroxysteroid dehydrogenases of adult male and female rat kidney show significant sex differences in their activities. Interference with the organisms endocrine balance (gonadectomy on day 25 of life, hypophysectomy on day 50, a combination of both these operations, administration of testosterone or oestradiol) demonstrates that the sexually differentiated enzyme activities may be classified as androgen or oestrogen dependent, the respective sex hormone acting either in an inductive or repressive manner. The criteria for androgen dependency (microsomal 3alpha- and 20beta-, cytoplasmic 17beta- and 20alpha- hydroxysteroid dehydrogenase) are the feminization of the enzyme activity in male animals after castration and the masculinization of the activity in male and female castrates as well as in normal female animals after administration of testosterone. This latter effect on normal females cannot be a testosterone mediated inhibition of ovarian function since ovariectomy has no effect. For 3alpha-, 20alpha-, and 20beta-hydroxysteroid dehydrogenase the effects of hypophysectomy parallel those of gonadectomy. However, after hypophysectomy the activity of 17beta-hydroxysteroid dehydrogenase falls significantly below the gonadectomized level. The androgen effect on 3alpha and 20beta-hydroxysteroid dehydrogenase is independent of the hypophysis, whereas that of 17beta- and 20alpha-hydroxysteroid dehydrogenase is mediated by the hypophysis.     

Sex hormone receptors in the hypothalamus and their role in the sexual differentiation of the brain of male rats

The content of receptors to estradiol and testosterone was determined in cytoplasmic and nuclear fractions of hypothalamus and brain cortex of male rats in the early postnatal period. Receptors to both estradiol and testosterone were revealed in cytosol and nuclear fractions, with the decrease in their concentration observed from days 1 to 5. The data obtained demonstrate that receptors to sexual hormones take part in the brain differentiation and regulation of hypophysis gonadotropic function by male or female type.     

Sex-related differences in blood and gonad levels of testosterone in silver fox fetuses

The mass of silver fox fetuses of both sexes, their gonads, and adrenals, and the levels of testosterone in blood serum and in gonads and adrenals were determined from day 31 of gestation and every five days thereafter until its termination. Marked sex-related differences were revealed: the blood and gonad levels of testosterone in male fetuses were much higher than those in female fetuses. The fetal adrenals contained significantly less testosterone than the gonads. No sex-related differences in the content of testosterone in the fetal adrenals were found. No differences were found in the body and adrenal mass in female and male fetuses at all the developmental stages studied, while the mass of ovaries exceeded that of testes from day 45 of gestation. The data obtained suggest sex dimorphism in the production of testosterone by gonads in silver foxes appears after day 35 and appears to correspond to the period of morphological differentiation of gonads.     

Sex-Related Differences in Blood and Gonad Levels of Testosterone in Silver Fox Fetuses

The mass of silver fox fetuses of both sexes, their gonads, and adrenals, and the levels of testosterone in the blood serum and in gonads and adrenals were determined from day 31 of gestation and every five days thereafter until its termination. Marked sex-related differences were revealed: the blood and gonad levels of testosterone in male fetuses were much higher than those in female fetuses. The fetal adrenals contained significantly less testosterone than the gonads. No sex-related differences in the content of testosterone in the fetal adrenals were found. No differences were found in the body and adrenal mass in female and male fetuses at all the developmental stages studied, while the mass of ovaries exceeded that of testes from day 45 of gestation. The data obtained suggest sex dimorphism in the production of testosterone by gonads in silver foxes appears after day 35 and appears to correspond to the period of morphological differentiation of gonads.     

Regulation by Androgen of Levels of the β Subunit of Nerve Growth Factor and Its mRNA in Selected Regions of the Mouse Brain

Abstract: Our previous studies showed that the concentration of the β subunit of nerve growth factor (β-NGF) in nervous tissues is higher in male than in female mice. To identify the brain regions that are affected by androgens, the amounts of β-NGF protein and its mRNAs were measured in male, female, and castrated male CD-1 mice and testicular feminization mice at 3–4 months of age. Among tissues examined, the hypophysis of males contained the highest average concentration of β-NGF protein. In most regions of the brain, individual levels were more variable in males than in females. However, after the castration, such variations in β-NGF levels disappeared. Average levels of β-NGF protein in males were higher in the cerebellum (eightfold higher), olfactory bulb (12-fold higher), hypothalamus (sixfold higher), and hypophysis (72-fold higher) than thope in corresponding regions of females. No significant differences were observed in levels of β-NGF protein in the hippocampus, cerebral cortex, striatum, septum, and brainstem. The castration of male mice caused a reduction in levels of β-NGF protein in the hypothalamus and hypophysis, but not in the cerebellum and olfactory bulb, to the femgle levels. The concentrations of β-NGF protein in testicular feminization mice were similar to those in female CD-1 mice in all regions. The concentrations of mRNA for β-NGF in the olfactory bulb and hypophysis from males were higher than those from females. By contrast, northern blots showed no remarkable differences in the amounts of brain-derived neurotrophic factor and neurotrophin-3 between the two sexes. Thus, in some regions of the brain, the production of β-NGF appears to be regulated by testosterone, but the regulatory mechanisms do not appear to be simple. Our present results indicate that the binding of testosterone to its receptor is an important step in the regulation of the level of β-NGF in these region.