Yang J Y, Pan J T
Institute of Physiology, National Yang-Ming Medical College, Taipei, Taiwan, Republic of China.
Neuroendocrinology. 1994 Jun;59(6):520-7. doi: 10.1159/000126701.
The involvement of the tuberoinfundibular dopaminergic (TIDA) neurons in the genesis of hyperprolactinemia in female thyroidectomized rats treated with estrogen was the focus of this study. Rats that were ovariectomized (3 weeks), thyroidectomized (2 weeks) and treated with estrogen for 6 days had a 5- to 10-fold increase in serum prolactin (PRL) levels, while the rats receiving the same treatments but without estrogen had lower PRL levels. The activity of TIDA neurons, using dihydroxyphenylacetic acid (DOPAC) concentration or the DOPAC/dopamine (DA) ratio in the median eminence (ME) as an index, was increased and decreased in estrogen-treated and untreated rats, respectively. The increases in serum PRL level and the activity of TIDA neurons were dependent on the duration of thyroidectomy and could both be lowered by daily injection of thyroid hormone (20 or 100 micrograms/kg b.w. thyroxine, i.p.) for 12 days in a dose-dependent manner. Using dihydroxyphenylalanine (DOPA) accumulation in the ME as another index, we also found an increased DOPA/DA ratio in estrogen-treated hypothyroid rats, which effect could be reversed by replacement of thyroid hormone. Furthermore, treatments with bromocryptine (3 mg/kg b.w./day, s.c.) for 3 days or with cysteamine (100 mg/kg b.w., s.c.) at 26, 15 and 2 h before the rats were sacrificed lowered both serum PRL level and TIDA neuron activity. Since PRL can exert a short-loop feedback control on its own secretion, these results indicate that the increased serum PRL levels in estrogen-treated hypothyroid female rats should be the cause, but not the result, of the increased activity of TIDA neurons.
本研究的重点是，在接受雌激素治疗的雌性甲状腺切除大鼠中，结节漏斗多巴胺能（TIDA）神经元与高催乳素血症发生之间的关系。卵巢切除（3周）、甲状腺切除（2周）并接受雌激素治疗6天的大鼠，其血清催乳素（PRL）水平升高了5至10倍，而接受相同处理但未使用雌激素的大鼠PRL水平较低。以中缝隆起（ME）中3,4-二羟基苯乙酸（DOPAC）浓度或DOPAC/多巴胺（DA）比值为指标，雌激素处理组和未处理组大鼠的TIDA神经元活性分别升高和降低。血清PRL水平的升高和TIDA神经元的活性取决于甲状腺切除的持续时间，并且每日腹腔注射甲状腺激素（20或100微克/千克体重甲状腺素）12天，二者均可呈剂量依赖性降低。以ME中左旋多巴（DOPA）蓄积量作为另一指标，我们还发现雌激素处理的甲状腺功能减退大鼠中DOPA/DA比值升高，补充甲状腺激素可逆转这一效应。此外，在处死大鼠前3天用溴隐亭（3毫克/千克体重/天，皮下注射）或在处死前26、15和2小时用半胱胺（100毫克/千克体重，皮下注射）处理，均可降低血清PRL水平和TIDA神经元活性。由于PRL可对其自身分泌发挥短反馈调节作用，这些结果表明，雌激素处理的甲状腺功能减退雌性大鼠血清PRL水平升高应是TIDA神经元活性增加的原因，而非结果。
