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Endocrine control of sexual development in the male guppy Pandey, Satyendra

Abstract

The role of pituitary and gonadal steroids in the development and maintenance of the testis and secondary sex characters of the guppy Poecilia reticulata Peters has been studied by the technique of surgical hypophysectomy and chemical inhibition of gonadotropic action using 'methallibure’. Hypophysectomy of juvenile or adult guppies completely blocks mitosis in the spermatogonia and their transformation into spermatocytes. However, spermatocytes, spermatids and sperm already present in the adult testis at the time of operation transform into spermatophores. In the absence of the pituitary, the spermatophores rupture after eight weeks and the resulting sperm are phagocytosed within the sperm ducts. Sertoli cells, interstitial cells and the epithelial cells lining the sperm ducts regress in hypophysectomized fish. Testosterone treatment of the hypophysectomized adult guppy initiates spermatogonial multiplication and the transformation of spermatogonia into spermatocytes; the regressed Sertoli cells, interstitial cells and the epithelial cells lining the sperm ducts resume their normal appearance. Testosterone treatment of hypophysectomized juvenile guppies does not initiate spermatogenesis but the sperm ducts become well differentiated. Of two particularly well differentiated secondary sex characters of the adult male guppy, the gonopodium (modified anal fin) remains unaffected after hypophysectomy whereas the lipophores (yellow and red pigments) present on the sides of body become obscure or entirely disappear in the absence of pituitary; the lipophores reappear after testosterone treatment. Secondary sex characters never appear in guppies hypophysectomized as juveniles. When hypophysectomized juveniles are treated with testosterone, secondary sex characters (gonopodium and lipophores) become evident. The regression of the gametogenetic and the steroidogenetic tissues in the testis of 'methallibure'-treated (1:10⁶ parts) adult guppy is not as complete as in the hypophysectomized fish. This indicates that the release of pituitary gonadotropins is not completely blocked. With the same dose of 'methallibure', however, the gonadotropin release in the juveniles is apparently blocked. In both adult and juvenile guppies 'methallibure' brings about a clear decrease in both the number and mean cell diameter of gonadotrophs. The gonadotropic hormone blocking activity of the compound seems to occur at the level of hormone synthesis. From these studies it has been concluded that mitotic division of spermatogonia and their transformation into spermatocytes are dependent on pituitary, but the transformation of spermatocytes, spermatids and sperm into spermatophores are pituitary-independent. The release of spermatophores is under the control of pituitary. The regressed Sertoli cells, interstitial cells and the epithelial cells lining the sperm ducts of hypophysectomized fish assume normal appearance with testosterone treatment. The appearance of secondary sex characters in hypophysectomized juveniles treated with testosterone indicates that secondary sex characters are directly controlled by testosterone. 'Methallibure' completely blocks the synthesis of gonadotropic hormones in the juvenile guppies but not in adults.

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