Pituitary gonadotropin-releasing hormone (GnRH) receptor activity in goldfish and catfish: seasonal and gonadal effects |
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| Authors: | H R Habibi R De Leeuw C S Nahorniak H J Th Goos R E Peter |
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| Institution: | (1) Department of Zoology, University of Alberta, Edmonton, Alberta, Canada;(2) Department of Experimental Zoology, Research Group for Comparative Endocrinology, University of Utrecht, Utrecht, The Netherlands;(3) Present address: Department of Biological Sciences, University of Calgary, 2500 University Drive N.W., Calgary, Alberta, Canada, T2N 1N4;(4) Department of Biological Sciences, University of Calgary, 2500 University Drive N.W., Calgary, Alberta, Canada, T2N 1N4 |
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| Abstract: | The goldfish pituitary contains two classes of gonadotropin-releasing hormone (GnRH) binding sites, a high affinity/low capacity
site and a low affinity/high capacity site (Habibiet al. 1987a), whereas the catfish pituitary contains a single class of high affinity GnRH binding sites (De Leeuwet al. 1988a). Seasonal variations in pituitary GnRH receptor binding parameters, and the effect of castration on pituitary GnRH
receptor binding were investigated in goldfish and catfish, respectively. In goldfish, GnRH receptors undergo seasonal variation
with the highest pituitary content of both high and low affinity sites occurring during the late stages of gonadal recrudescence.
The observed changes in pituitary GnRH receptor content correlate closely with responsiveness to a GnRH agonistin vivo in terms of serum gonadotropin (GTH) levels. In catfish, castration results in a two-fold increase in pituitary GnRH receptor
content, which can be reversed by concomitant treatment with androstenedione, but not by the non-aromatizable androgen 11β-hydroxyandrostenedione;
changes observed in GnRH receptor content correlate with variations in serum GTH levels and responsiveness to a GnRH agonist.
In summary, the present study provides a clear evidence for seasonal variation in pituitary GnRH receptor activity in goldfish,
and demonstrates a gonadal feedback mechanism regulating GnRH receptor activity in the catfish pituitary. |
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| Keywords: | Carassius auratus Clarias gariepinus reproduction gonadotropin luteinining hormone releasing hormone (LHRH) receptors steroid castration sexual cycle |
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