Summary: | Complete testicular maturation was induced in silver eels. kept at 24° in fresh water. by a single injection of 1000 I.U. of heterologous gonodotropin (hCG). Each week. far 4 weeks. some eels were examined far testis structural pattern. plasma sex steroids, and gonad cytosoI steroid receptors. The first effect of the hCG was on the tubular organization of the testis. followed by spermatogenesis. Plasma androgens were not detectable in the untreated eels, whereas a peak was detected a week after in those treated with the injection and afterward a decline. Plasma progesterone and estradiol showed a peak 2 weeks after treatment. Untreated eel gonads showed a high content of cytosolic free estradiol receptors which disappeared in the hCG-treated ones. a peak of free progesterone receptors was found I week after injection. The results are discussed in relation to the differentiation and maturation of eels testes.
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