Untersuchungen zur Wirkung von östrogenwirksamen Stoffen auf die Gonadenentwicklung bei Fröschen (Rana temporaria und Xenopus laevis) sowie ultrastrukturelle und immunhistochemische Untersuchungen an Froschgonaden (Rana temporaria)

The influence of estrogen-like substances on the gonadal development in frogs (Rana temporaria and Xenopus laevis). Ultrastructural and immunohistochemical investiga-tions on the gonads of frogs (Rana temporaria). The aim of the present thesis was the investigation and assessment of the estrogen pollu-tion of a river in South-Germany above and below a sewage plant outlet and its possible effects on the gonadal development in amphibians. In an exposure experiment with differ-ent sewage dilutions the effect on the indigenous gras frog (Rana temporaria) were com-pared with the effects on the African claw frog (Xenopus laevis). Because of the lack of relevant data in current literature it was necessary to first collect some basic data on light microscopy, ultrastructure and immunohistochemistry with reference to frogs. Furthermore the sexual differentiation of two populations of different origin were compared histologically. Characterisation of the gonads The ovaries of Xenopus laevis displayed a garland-like structure in contrast to the compact ovaries of Rana temporaria. The ovaries of both frog species were surrounded by an epi-thelium and filled with germ cells which enclosed an ovarian cavity. The oogonies were mainly found in the peripheral parts of the organ. The oocytes were characterised by a big and irregularly shaped cell nucleolus with peripherally located nucleoli. They were sur-rounded by a thin one-layered follicular epithelium. Electron microscopical examination of the ovaries of Rana temporaria showed elongated tubular mitochondria in the cytoplasm which were found exclusively in oocytes. Some of the mitochondria from subadult frogs contained yolk crystals. Additionally an accumulation of electron-tight Granule was found just below the plasma membrane, which could be a preliminary stage of the cortical granule. The testis of the frogs were enveloped by an epithelium and a tunica albuginea which al-ready showed a tubular structure. The testis from Rana temporaria and the Xenopus laevis differed in their developmental stages. The testis of juvenile Rana temporaria contained only germ cells whereas the testis of some Xenopus laevis already contained spermato-cytes and spermatozoa. The spermatocysts, characteristic of frog testis, could be seen in conjunction with the appearance of spermatocytes only. By using light microscopy two different types of germ cells in both frog species could be distinguished which probably were primary and secondary germ cells. By electron microscopical investigation of the testis of Rana temporaria the somatic cells could, on the basis of location and morphology, be differentiated in two types. The somatic cells of the first type were located inside the Tubuli seminiferi and have probably the same function as the Sertoli cells of mammals. The cells of the second type, the Leydig cells or interstitial cells, were located outside the Tubuli and were characterized by granular vesicle in the cytoplasm. With view to the sexual differentiation of Rana temporaria a comparative histological inves-tigation of the gonads of juvenile and subadult frogs of a native midland population and a high alpine population was performed. The midland population proved to be a sexually semi-differentiated species since apart from clearly male or female animals it also com-prises intersex individuals in different stages of the transformation process. The genotypi-cally male animals developed female gonads in the first place which secondly converted into testis during a hermaphrodite stage. The transformation process from female into male gonads was, on the basis of morphological criteria, classified into three stages. The highal-pin population on the other hand proved to be a sexually differentiated race. By using the Avidin-Biotin-Complex-Technique five different antibodies were tested on the gonadal tissue of juvenile and subadult Rana temporaria. The test for Laminin, a non-collagen glycoprotein, which is part of the basal membrane in mammals, resulted in a posi-tive reaction. It seems therefore that similar to Laminin in mammals a glycoprotein plays an important part in the basal membrane of frogs. α-Actin, a fibrous protein of the smooth muscles, which was detected in the Theca externa of the layer of follicle cells in different species, could be established in the blood vessel wall only and not in the layer of follicle cells. Furthermore the occurrence of a Zona pellucida by using antibodies against the por-cine glycoprotein ZP3 was investigated. The ovum including the surrounding layer of follicle cells showed a negative reaction which however did not implicitly exclude the occurrence of a glycoprotein layer with a different antigenicity. Until now the existence of a glycoprotein layer in anurans, in connection with microscopical anatomy of ovaries in Rana temporaria or other species of frogs has not been mentioned in references. The examination of the go-nadal tissue as to the occurrence of ACE (Angiotensin Converting Enzymes) turned out negative as well. Example of application With the exception of a temporarily higher concentration of alkylphenol in the beginning of the exposure, the chemical analyses revealed a relatively low degree of pollution with alcyl-phenols and steroids. The results were comparable to other results of German rivers and stayed well below other European comparative data. According to the results of this study the current level of pollution of the experimental water with estrogens does not endanger the amphibian population. The examination did not reveal any influence of the sewage on the embryonal and larval development. Furthermore, the histological investigation of the gonads in exposed and unexposed frogs with reference to the gonadal sexual differentia-tion as well as the sex ratios did not reveal significant changes. There was no correlation as to the frequency of the occurrence of intersex in the groups of exposed and unexposed frogs, neither of Xenopus laevis nor of Rana temporaria. Only the transformation process from ovaries to testis of the sexually semi-differentiated species of Rana temporaria was slowed down in the group of exposed animals in contrast to unexposed animals. The rea-son for this phenomenon could be the inhibitive influence of the low-level but more continu-ous estrogen pollution in sewage than in river water. Conversely, a link between the accel-eration of the transformation process within the group of unexposed animals and the tem-porarily higher alkylphenol level in the beginning of the exposure cannot completely be ruled out. According to references alkylphenol can cause an increase of testosterone. The semiquantitative RT-PCR detecting Vitellogenin-mRNA carried out by the Institute of Freshwater Ecology and Inland Fisheries in Berlin showed a minor increase in females of Xenopus laevis which were exposed to sewage in the ration of a 2:1 dilution in contrast to the unexposed animals. Taking into account the synergistic effects of estrogens, the in-crease could be attributed to the higher estrogen pollution of the sewage. The histopa-thological analysis for the detection of toxical effects of the sewage as well as other poten-tial influential factors provided no hints as to a possibly toxical influence of the sewage.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Ludwig-Maximilians-Universität

Year

2003

Author dc:creator

• Steineck, Cornelia

Repository record source_url

https://edoc.ub.uni-muenchen.de/1076/

OAI identifier oai:identifier

oai:edoc.ub.uni-muenchen.de:1076