FBA Translation (New Series) No. 136

Transcription

1 Freshwater Biological Association FBA Translation (New Series) No. 136 Title. Modulation of the effectiveness of 17 α-hydroxy-20 β-dihydroprogesterone or of a gonadotrophic extract on the in vitro intrafollicular maturation of oocytes of the Rainbow trout Salmo gairdnerii by various non-maturing steroids. Author(s) JALABERT B. Reference: C.r. hebd;seanc.acad.sci.,paris,ser.d. 281, Original language: French Date of publication of original: 1975 Translator: A.G. Cross Date of publication of translation: 1980 Number of pages of translation: 6 FBA Translations are to be considered as "provisional". As a rule they have not been prepared by expert translators, nor have, they been edited by the original authors. They are available from The Librarian, Freshwater Biological Association, The Ferry House, Far Sawrey, AMBLESIDE. Westmorland. England, at the current rate for xerox copying.

2 FBA TRANSLATION (NEW SERIES) No Modulation of the effectiveness of 17 α-hydroxy-20 β-dihydroprogesterone or of a gonadotropic extract on the in vitro intrafollicular maturation of oocytes of the Rainbow trout Salmo gairdnerii by various non-maturing steroids. B. Jalabert C.r. hebd.seanc.acad.sci.,paris,ser.d. 281, (1975) Translated by: A.G. Cross The effectiveness of 17 α-hydroxy-20 β-dihydroprogesterone (17 α-20 β Pg) or of a trout hypophyseal gonadotrophic extract on the in vitro intrafollicular maturation of trout oocytes can be modulated by steroids which do not have a direct maturing effect; the effectiveness of the gonadotrophic extract is lowered by oestradiol and oestrone and increased by testosterone. As these steroids have no significant effect on maturation induced by 17 α-20 β Pg, the site of their activity is probably in the follicular envelopes. Corticosteroids, and Cortisol and cortisone in particular increase the effectiveness of the gonadotrophic extract, but increase the effectiveness of 17 α-20 β Pg even more strongly, suggesting that this 'progestagen' has a direct effect on oocyte sensitivity. The most powerful steroid inducing oocyte maturation (the resumption of meiosis prior to ovulation) so far found in the trout 2), the pike 3) and even the crucian carp 4) is 17 α-hydroxy-20 β dihydroprogesterone (4 pregnene-17 α-20 β diol-3 one, abbreviation: 17 α-20 β Pg), a steroid isolated from the plasma of salmon - 1 -

3 in which it reaches very high levels at the time of spawning 6). In Oryzias latipes it is progesterone 7) and in Heteropneustes fossilis it is certain corticosteroids which are considered to be the most active inducers, but the hydroxyl derivatives of progesterone do not appear to have been estimated. In the trout 9,10) the active steroids are necessarily manufactured in the ovary, and more particularly in the follicle, as shown by the positive effect of gonadotrophic extracts in vitro on the oocyte-follicle unit (+ fragments of ovarian tissue). In Heteropneustes fossilis on the other hand gonadotrophic extracts appear to have no effect on the follicles in vitro 11,12) and various experimental factors would suggest a gonadotrophic relay through the internal organ which produces the corticosteroids which have a specific effect on maturation 13). In addition to this high levels of oestrogens, androgens and corticosteroids can be detected in different species of fish 6,14-16) near spawning time. As the majority of these steroids have no maturing effect on the trout in vitro when they are administered alone 9,10), we attempted to discover in this work whether they were capable of modifying the efficiency of the maturation of trout oocytes in vitro by modifying either the response of the follicle to a gonadotrophic extract, or the response of the oocyte to 17 α-20 β Pg. Materials and methods Incubations were carried out at 10 C using the technique already described 9,10), in the same isotonic medium which was however modified to have a ph of about 8, which is the optimum for maturation 4). Oocytes removed at the peripheral germinating vesicle stage were incubated in their follicle. For a given maturation treatment the theoretical dose resulting in 50% maturation (DE 50 ) was calculated using the method previously used for the biological estimation of gonadotrophic hormones in fish 17), after determining the percentage of vitelline maturations 10) as a function of variable doses

4 The reference maturation treatments were carried out using either 17 α-20 β Pg or a trout hypophyseal gonadotrophic extract (EPH: hypophyseal protein extract 17)) which were left in the presence of the follicles throughout the incubation period (72 to 96 hours). The relative effectiveness (E r ) of a maturation treatment in the presence of a non-maturing steroid 'S' (added simultaneously at a level of 1 μg/ml) is expressed by the ratio of the DE 50 for the reference maturation treatment to the DE 50 for the same treatment in the presence of 'S' (Figure: E r has a confidence limit of p = 95%. All E values were obtained from DE 50 values determined by incubating the follicles from one female). Steroids were dissolved in pure ethanol and added to the incubation medium at a level of 2.5 μl/ml. Relative effectiveness (E r ) of oocyte maturation induced by 17 α-20 β Pg (left hand side) or by a gonadotrophic extract (right hand side) in the presence of various non-maturing steroids

5 Results (Figure) Modification of the effectiveness of the gonadotrophic extract. - The effectiveness of this is reduced by oestradiol 17 β (E r significantly less than 1 in 3 out of 4) and oestrone (E r < 1, significantly in 2 out of 4). Testosterone, corticosterone, but above all Cortisol and cortisone increase the effectiveness of the gonadotrophic extract by a factor which rises up to 7 in the case of Cortisol. 11-ketotestosterone does not show any clearly repeatable effect. Modification of the effectiveness of 17 α-20 β Pg. - Oestradiol 17 β, oestrone and testosterone show no clear effect. The effectiveness of 17 α-20 β Pg seems to be slightly inhibited by the presence of 11-ketotestosterone; it is increased slightly by corticosterone and multiplied by a factor which can amount to 11 to 13 in the presence of cortisone and Cortisol. Discussion Follicles incubated in vitro comprise a complex system in which several components can react separately, simultaneously or consecutively: the oocyte, the follicular envelopes and the shreds of ovarian tissue adhering to the follicles. As a hypothesis (borne out by the experimental facts observed so far 4,9,10) the gonadotrophic extract would seem to act on the follicular envelopes (and the ovarian tissue) and 17 α-20 β Pg would appear to act directly on the oocyte short circuiting this relay. As far as the stimulating or inhibiting action of 'non-maturing' steroids alone is concerned, the comparison between differences in the effectiveness of 17 α-20 β Pg and the gonadotrophic extract provides an indication of their possible site of action. Thus without significantly modifying the effectiveness of 17 α-20 β Pg the oestrogens reduce the effectiveness of the gonadotrophic extract and testosterone increases it, which could mean that they act on the follicular envelopes. 11-ketotestosterone shows no clear activity; if it in fact had an inhibitory effect on maturation and ovulation as suggested by certain authors in the case of the mullet 18), our results show that this effect is not exerted directly on the follicle in the trout

6 Corticosteroids (primarily Cortisol and cortisone) certainly play a major part in sensitisation; they considerably increase the effectiveness of the gonadotrophic extract and produce an even greater increase in the effectiveness of 17 α-20 β Pg which would suggest that they play a leading part in sensitising the oocytes to 17 a-20 3 Pg, without excluding the possibility that the follicular envelopes may themselves be sensitised to the gonadotrophic activity. It should be recalled that these corticosteroids have no maturing activity as such in the trout in the doses used here (1 μg/ml), whereas the DE 50 of 17 α-20 β Pg is of the order of, 20 ng/ml 2,4). Bearing in mind work which would appear to have corticosteroids acting the part of mediators in oocyte maturation, irrespective of whether, these compounds are produced by the internal organ 6,13) or may even be produced in the ovary itself 19), we propose the following working hypothesis: depending upon environmental conditions, oocyte maturation may be initiated depending upon the species, or in a single species, either by a typical gonadotrophic discharge 20), or by an increase in the levels of circulating corticosteroids following an environmental stress (changes in the environment often linked with spawning in numerous fish) in the absence of such a discharge (the gonadotrophic level being in any case generally high at the termination of vitellogenesis 17), thus reducing the sensitivity threshold of the follicles below the level of the circulating gonadotrophic hormone and indirectly initiating the mechanisms of oocyte maturation. We have already discovered that Cortisol has a potentiating effect on in vitro intrafollicular oocyte maturation induced by a gonadotrophic extract in the pike 3) and the crucian carp 4). The above hypothesis, which may receive support from observations on other species, may perhaps assist in inserting the special case of the cat fish Heteropneustes fossilis 13) in a more general regulatory model. References 1) With technical assistance from Marie-Claire Theron and Micheline Heydorff, and the assistance of Claire Lebrun (DEA student). 2) A. Fostier, B. Jalabert and M. Terqui, Comptes rendus, Series D, 1973, 277, p

7 3) B. Jalabert and B. Breton, Gen. Comp. Endocr., 1973, 22, p ) B. Jalabert (donnees non publiees). 5) R.D. Idler, V.H.M. Fagerlund and A.P. Ronald, Biochim. Biophys. Res. Com., 1960, 2, p ) P.J. Schmidt and D.R. Idler, Gen. Comp. Endocr., 1962, 2, p ) T. Iwamatsu, Annot. Zool. Jap., 1974, 47, p ) B.I. Sundararaj and S.V. Goswami, Gen. Comp. Endocr., 1971, 17, p ) B. Jalabert, B. Breton and C. Bry, Comptes rendus. Series D, 1972, 275, p ) B. Jalabert, C. Bry, D. Szollosi and A. Fostier, Ann. Biol. anim. Bioch. Biophys., 1973, 13, p ) S.V. Goswami and B.I. Sundararaj, J.Exp. Zool., 1971, 178, p ) B.I. Sundararaj, S.V. Goswami and E.M. Donaldson, J. Fish. Res. Bd. Canada, 1972, 29, p ) B.I. Sundararaj and S.V. Goswami, Gen. Comp. Endocr., 1974, 23, p ) C.B. Schreck, R.T. Lackey and M.L. Hopwood, Copeia, 1972, p ) Y. Katz and B. Eckstein, Endocrinology, 1974, 95, p ) B. Breton, B. Jalabert, A. Fostier and R. Billard, J.Physiol., Paris, 1975, (in press). 17) B. Jalabert, B. Breton and R. Billard, Ann. Biol. anim. Bioch. Biophys., 1974, 14, p ) B. Eckstein and U. Eylath, Gen. Comp. Endocr., 1970, 14, p ) L. Colombo, H.A. Bern, J. Pieprzyk and D.W. Johnson, Gen. Comp. Endocr., 1973, 21, p ) B. Breton, R. Billard, B. Jalabert and G. Kann, Gen. Comp. Endocr., 1972, 18, p

8 Notice Please note that these translations were produced to assist the scientific staff of the FBA (Freshwater Biological Association) in their research. These translations were done by scientific staff with relevant language skills and not by professional translators.