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Identificação e doseamento de esteróides sexuais em machos de dourada (Sparus aurata) estimulados com LHRH A
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Abstract(s)
O presente estudo teve como objectivo analisar os mecanismos reguladores, particularmente a nível endócrino, da fase fnial da maturação dos gâmetas masculinos de dourada (Spams aurata), tendo-se efectuado um ensaio in vitro no qual se incubaram fragmentos de testículo com um precursor radiactivo para posterior analise dos metabolitos produzidos, e um ensaio de longa duração no qual se estudaram os efeitos da administração de um análogo da hormona libertadora da hormona luteiiiizante na espermiação e nos níveis de esteróides associados: 17b-estradiol,
17a,20a-dihidroxi-4-pregnen-3-ona, testosterona e 11-cetotestosterona-.
1°ensaio: Fragmentos de testículo de um macho em espermiação foram incubados com
17a-hidroxiprogesterona tritiada durante 24h e os metabolitos produzidos após vários tempos de incubação analisados. A taxa de conversão observada foi sempre muito reduzida, em particular durante as primeiras 8h de incubação. Os principais metabolitos encontrados foram a 11-cetotestosterona e a androsterona.
2°ENsAIO: Dez douradas de 1 ano de idade e 450g de peso médio, receberam 3 iiijecções de 4mg/kg de des-Giy10,[D-Aia6]-Nerh-LHRH em 250 ml de 0.8% NaCI, durante um período de 50 dias, que começou no início da época de postura (final de Setembro) . Outro grupo de 10 peixes foi injectado apenas com o veículo (controlo). No final da experiência não se observaram diferenças significativas no número de peixes em espermiação e nos índices gonadossomáticos entre os dois grupos. No entanto a percentagem média de tecido masculino da gónada era 70% no controlo enquanto que no grupo tratado, onde o tecido feminino predominava, era apenas 30%.
Não foram encontradas diferenças significativas nos níveis de nenhum dos esteróides (livres ou conjugados) analisados, nem nenhuma relação entre o tratamento e as variações dos vários esteróides. Estes resultados indicam que a LHRH poderá estar involvida no processo de inversão sexual da dourada.
The present study was performed in order to investigate the endocrine mecanisms that control the final maturation of the male gametes of gilthead seabream (Spams aurata). Two experiments were performed, the first was an in vitro assay, where testis from a spermiating male were incubated with radioactive precursor in order to determine the products formed, the second was a long term experiment witli the objective of studying the long term effect of luteinizing hormone releasing along on spermiation and steroid levels: estradiol-17b, 17a,20a-dihydroxy-4-pregnen-3-one, testosterone and 11-ketotestosterone. 1st EXPERIMENT: Fragments of testicular tissue were incubated with tritiated l7a-hydroxyprogesterone during a 24h period and the products formed after several icicubation times were analised. The conversion rate was very low particulary during the first 8h of incubation. The major products were identified as 11-ketotestosterone and androsterone. 2 nd EXPERIMENT: Ten one-year-old fish 450g average weight received fortnightly 3 injections of 4mg/kg of des-Glylo,[D-Aia6]-Nerh-LHRH in 250ml of {0.8% NaCI, over a period of 50 days. Another group of 10 fish were injected witli the saline solution only (control). The experirnent started at the end of September at the begining of the spawniiig season. At the end of experiment there were no significant differences in the number of spermiating fish and gonadossomatic indexes between groups. However, the average percentage volume of male gonadal tissue was 70% in the control group as compared to 30% in the LHRHa group where female tissue predominated. No significant changes in steroid levels (free and conjugated) were observed. Steroid differences between groups could not be related to the effect of treatment. The results indicate that LHRH could be involved in the process of sex change in gilthead seabream.
The present study was performed in order to investigate the endocrine mecanisms that control the final maturation of the male gametes of gilthead seabream (Spams aurata). Two experiments were performed, the first was an in vitro assay, where testis from a spermiating male were incubated with radioactive precursor in order to determine the products formed, the second was a long term experiment witli the objective of studying the long term effect of luteinizing hormone releasing along on spermiation and steroid levels: estradiol-17b, 17a,20a-dihydroxy-4-pregnen-3-one, testosterone and 11-ketotestosterone. 1st EXPERIMENT: Fragments of testicular tissue were incubated with tritiated l7a-hydroxyprogesterone during a 24h period and the products formed after several icicubation times were analised. The conversion rate was very low particulary during the first 8h of incubation. The major products were identified as 11-ketotestosterone and androsterone. 2 nd EXPERIMENT: Ten one-year-old fish 450g average weight received fortnightly 3 injections of 4mg/kg of des-Glylo,[D-Aia6]-Nerh-LHRH in 250ml of {0.8% NaCI, over a period of 50 days. Another group of 10 fish were injected witli the saline solution only (control). The experirnent started at the end of September at the begining of the spawniiig season. At the end of experiment there were no significant differences in the number of spermiating fish and gonadossomatic indexes between groups. However, the average percentage volume of male gonadal tissue was 70% in the control group as compared to 30% in the LHRHa group where female tissue predominated. No significant changes in steroid levels (free and conjugated) were observed. Steroid differences between groups could not be related to the effect of treatment. The results indicate that LHRH could be involved in the process of sex change in gilthead seabream.