FUNCTIONAL SPECIFICITY FOR SALMON GONADOTROPIN-RELEASING-HORMONE (GNRH) AND CHICKEN GNRH-II COUPLED TO THE GONADOTROPIN-RELEASE AND SUBUNIT MESSENGER-RIBONUCLEIC-ACID LEVEL IN THE GOLDFISH PITUITARY

被引:87
作者
KHAKOO, Z [1 ]
BHATIA, A [1 ]
GEDAMU, L [1 ]
HABIBI, HR [1 ]
机构
[1] UNIV CALGARY, DEPT BIOL SCI, CALGARY T2N 1N4, AB, CANADA
关键词
D O I
10.1210/en.134.2.838
中图分类号
R5 [内科学];
学科分类号
1002 ; 100201 ;
摘要
GnRH is the key regulator of reproduction in the vertebrates. In this study, we investigated the release and synthesis of maturational gonadotropin hormone (GTH-II) stimulated by native GnRH forms, salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), in the goldfish pituitary. The experimental approach was to study the differences between desensitization induced by sGnRH and cGnRH-II administered in homologous and heterologous fashion. Pulsatile alternate treatments with sGnRH and cGnRH-II (i.e. sGnRH/cGnRH-II or cGnRH-II/sGnRH) at 10(-8) M (every 30 min) resulted in a lower degree of desensitization compared with homologous treatments with either sGnRH or cGnRH-II (sGnRH/sGnRH or cGnRH-II/cGnRH-II), or when combined together (sGnRH + cGnRH-II). We also investigated the effects of continuous treatments with sGnRH and cGnRH-II, administered in a homologous or heterologous fashion. Increasing concentrations of either sGnRH or cGnRH-II (10(-8)-10(-6) M) administered continuously (60 min) in a homologous fashion resulted in significant desensitization of the pituitary GTH-II release. Alternate continuous treatments with sGnRH and cGnRH-II (i.e. sGnRH/ cGnRH-II/sGnRH or cGnRH-II/sGnRH/cGnRH-II) resulted in lower degree of desensitization compared to homologous treatments, particularly at lower doses. We further investigated the effects of sGnRH and cGnRH-II on GTH-II beta and GTH-II alpha subunit messenger RNA (mRNA) levels in the goldfish pituitary. In sexually regressed animals, sGnRH treatment (4 mu g/fish) increased the accumulation of GTH-II beta and GTH-II alpha mRNA, whereas cGnRH-II treatment was without effect. In sexually mature animals, however, both cGnRH-II and sGnRH stimulated accumulation of GTH-II beta and GTH-II alpha mRNA, with cGnRH-II exerting a greater effect on GTH-II subunit mRNA production. These results suggest a differential control of GTH-II subunit gene expression or mRNA stabilization by sGnRH and cGnRH-II in the goldfish pituitary based on the stage of gonadal recrudescence. In general, the present findings support the hypothesis that sGnRH and cGnRH-II regulate the release and synthesis of GTH-II through different receptor-effector mechanisms in the goldfish pituitary.
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页码:838 / 847
页数:10
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