Tyrosine hydroxylase in the stalk-median eminence and posterior pituitary is inactivated only during the plateau phase of the preovulatory prolactin surge.
Tyrosine hydroxylase in the stalk-median eminence and posterior pituitary is inactivated only during the plateau phase of the preovulatory prolactin surge.
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DOI：
10.1210/endo-125-2-667
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发表时间：
1989-08
期刊：
影响因子：
4.8
通讯作者：
L. Arbogast;N. Ben-Jonathan
中科院分区：
文献类型：
--
作者：
L. Arbogast;N. Ben-Jonathan
本研究检测了排卵前PRL峰期垂体柄正中隆起（SME）和垂体后叶（PP）中酪氨酸羟化酶（TH）活性的变化。未成熟的雌性大鼠在第28天注射PMSG。血PRL水平在第30天早晨较低，从1400-1600 h上升到峰值，从1800-2400 h保持在较低的平台，并在第31天早晨下降到基础水平。SME，PP和纹状体从PMSG处理的大鼠在排卵期的选定时间和年龄匹配的对照组大鼠。TH活性测定在组织匀浆通过耦合羟基化-脱羧测定。从底物饱和曲线估计相对于6-甲基四氢蝶呤的表观Km和最大速度值。TH在SME或PP的对照大鼠的动力学参数是相似的，在1100和1800小时的第30天。然而，在这两个组织的表观Km显着低于纹状体。TH在SME和PP的亲和力是不变的，在PRL激增的高峰期之前和期间，在后期的平台期显着减少，并在第31天的早晨恢复到presurge水平。在纹状体TH活性是相似的，在所有时间检查。为了确定酶的活化状态，将组织匀浆与cAMP、ATP和镁一起预孵育。TH活性在SME在高峰期不受cAMP，并在PP适度增加。相对不活跃的酶在这两个组织在平台期显着激活cAMP依赖性机制。纹状体TH的低亲和力大大增加cAMP在这两个时间。这些数据表明，TH在SME和PP存在于激活状态的大部分时间，是短暂失活的平台期的PRL激增。相比之下，TH在纹状体是相对不活跃的基础状态，不受激素变化引起的PMSG。我们的结论是峰值PRL激增发生，尽管活跃的多巴胺（DA）神经元，这表明它是由一个nondopaminergic机制。在SME和PP的DA神经元中TH活性的降低可能延长平台期的PRL浪涌，而DA活性的增加与浪涌的终止相一致。
This study examined changes in the activity of tyrosine hydroxylase (TH) in the stalk-median eminence (SME) and posterior pituitary (PP) during the preovulatory PRL surge. Immature female rats were injected with PMSG on day 28. Blood PRL levels were low on the morning of day 30, rose to a peak from 1400-1600 h, remained at a lower plateau from 1800-2400 h, and declined to basal levels on the morning of day 31. SME, PP, and striatum were removed from PMSG-treated rats at selected times during the periovulatory period and from age-matched control rats. TH activity was determined in tissue homogenates by a coupled hydroxylation-decarboxylation assay. Apparent Km and maximum velocity values with respect to 6-methyl tetrahydropterine were estimated from substrate saturation curves. The kinetic parameters for TH in either the SME or the PP of control rats were similar at 1100 and 1800 h on day 30. However, the apparent Km in both tissues was significantly lower than that in the striatum. The affinity of TH in the SME and PP was unchanged before and during the peak phase of the PRL surge, reduced significantly during the late plateau, and returned to presurge levels in the morning of day 31. TH activity in the striatum was similar at all times examined. To determine the state of activation of the enzyme, tissue homogenates were preincubated with cAMP, ATP, and magnesium. TH activity in the SME during the peak phase was unchanged by cAMP, and that in the PP was modestly increased. The relatively inactive enzyme in both tissues during the plateau phase was markedly activated by a cAMP-dependent mechanism. The low affinity of striatal TH was greatly increased by cAMP at both times. These data suggest that TH in the SME and PP exists in an activated state most of the time and is transiently inactivated during the plateau phase of the PRL surge. In contrast, TH in the striatum is relatively inactive in the basal state and is not affected by hormonal changes induced by PMSG. We conclude that the peak PRL surge occurs in spite of active dopamine (DA) neurons, suggesting that it is generated by a nondopaminergic mechanism. Decreased TH activity in DA neurons in the SME and PP may prolong the PRL surge during the plateau phase, whereas increased DA activity coincides with the termination of the surge.