摘要
The effect of estradiol-17β (E2)treatment on the pituitary-thyroidal axis has been investi- gated in female Japanese eels in seawater. The eels were injected with 1 mg/kg body weight (BW) weekly for two to eight weeks; another group was treated with 5 mg/kg BW weekly for eight weeks and sacrificed three days after the last injection. In the pituitary, using RT-PCR systern, the thyroid stim- ulating hormone 3 subunit mRNA (TSHβ MRNA) level is slowly increased in the low-dose E2 treatment group. A significant increase in values occurred after eight weeks E2 injections. The histological structure of the thyroid follicles suggests a hypo-activity as shown by a reduced epithelial cell height in eels injected with E2 after six and eight times, and eventually reached a minimum level after eight weeks. Using ra- dioimmunoassay of thyroxine (T4),triiodothyronine (T3) in the serum, a slowly decrease of both hor- mones is demonstrated. On the other hand, the TSHβ mRNA level is significantly increased from initial in the high-dose E2 treatment group. The histological structure of the thyroid follicles suggests a hypo- activity, and a sharp decrease of the both hormones is also indicated. These data suggest that the expres- sion of TSHβ mRNA level is increased and thyroid hormone release is depressed by E2, the effects de- pend upon E2 inection period and dose. Furthermore, E2 could not directly influence the TSHβ mRNA expression and, TSH transcription might be controlled by a negative feedback of thyroid hormone.
The effect of estradiol-17β (E2)treatment on the pituitary-thyroidal axis has been investi- gated in female Japanese eels in seawater. The eels were injected with 1 mg/kg body weight (BW) weekly for two to eight weeks; another group was treated with 5 mg/kg BW weekly for eight weeks and sacrificed three days after the last injection. In the pituitary, using RT-PCR systern, the thyroid stim- ulating hormone 3 subunit mRNA (TSHβ MRNA) level is slowly increased in the low-dose E2 treatment group. A significant increase in values occurred after eight weeks E2 injections. The histological structure of the thyroid follicles suggests a hypo-activity as shown by a reduced epithelial cell height in eels injected with E2 after six and eight times, and eventually reached a minimum level after eight weeks. Using ra- dioimmunoassay of thyroxine (T4),triiodothyronine (T3) in the serum, a slowly decrease of both hor- mones is demonstrated. On the other hand, the TSHβ mRNA level is significantly increased from initial in the high-dose E2 treatment group. The histological structure of the thyroid follicles suggests a hypo- activity, and a sharp decrease of the both hormones is also indicated. These data suggest that the expres- sion of TSHβ mRNA level is increased and thyroid hormone release is depressed by E2, the effects de- pend upon E2 inection period and dose. Furthermore, E2 could not directly influence the TSHβ mRNA expression and, TSH transcription might be controlled by a negative feedback of thyroid hormone.
