Pituitary-gonadal Relationship in the Catfish Clarias batrachus (L) : A Study Correlating Gonadotrophin-II and Sex Steroid Dynamics(Endocrinology)
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概要
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A heterologous radioimmunoassay was developed for measuring gonadotrophin-ll (GTH-II) in the catfish Clarias batrachus. Serum and/or pituitary levels of GTH-II showed significant annual/seasonal variations in male and female catfish, which could be correlated with both gonadosomatic index and/or serum testosterone level. GTH-II was not detected in resting phase, increased during gonadal recrudescence to peak values in late prespawning/spawning phases, and declined to low values in postspawning phase. During gonadal recrudescence, the pituitary and serum levels of GTH-II maintained positive or inverse relationships implying differential rates of hormone release and synthesis/storage. Gonadectomy resulted in increased release of GTH-II ; the release pattern varied in females and hemi-castrated or completely castrated males. In females, the GTH-II increase followed a distinct biphasic pattern with the peak rise at week 4 of ovariectomy. In males, castration resulted in significant rise of serum GTH-II levels at all duration except week 5, but the magnitude of the rise was higher in completely castrated fish (weeks 1, 2 and 3). Testosterone replacement in 3-week hemi-castrated fish restored the GTH-II level to that of the sham control vehicle group. In intact fish, administration of testosterone elicited an increase in serum GTH-II levels in the low dose (0.25 and 0.5 μg / g BW) groups and no change in the high dose (1.0 μg / g BW) group. Methallibure treatment inhibited GTH-II levels in a dose-dependent manner. The reduction was greater in males. Withdrawal of the drug treatment restored the GTH-II and testosterone levels after 15 days in the low dose group (2 μg / g BW). The results indicate that there exists a dynamic positive or negative feedback relationship between gonadal steroids and GTH-II, which is essential to control the release and availability of circulating GTH-II.
- 2000-04-10
著者
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Singh M.
Department Of Botany Punjab Agricultural University
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Goos H.
Department Of Experimental Zoology University Of Utrecht
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Joy K.
Department of Zoology, Banaras Hindu University
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Senthikumaran B.
Laboratory of Reproductive Biology, National Institute for Basic Biology
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Senthikumaran B.
Laboratory Of Reproductive Biology National Institute For Basic Biology
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Joy K.
Department Of Zoology Banaras Hindu University
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Joy K.P.
Department of Zoology, Banaras Hindu University
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Singh M.S.
Department of Zoology, Banaras Hindu University
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