Discriminative effects of testosterone on hypothalamic luteinizing hormone-releasing hormone levels and luteinizing hormone secretion in castrated male rats: analyses of dose and duration characteristics.
Discriminative effects of testosterone on hypothalamic luteinizing hormone-releasing hormone levels and luteinizing hormone secretion in castrated male rats: analyses of dose and duration characteristics.
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DOI：
10.1210/endo-111-1-24
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发表时间：
1982-07
期刊：
影响因子：
4.8
通讯作者：
P. Kalra;S. Kalra
中科院分区：
文献类型：
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作者：
P. Kalra;S. Kalra
我们之前报道过，在阉割的雄性大鼠中，性腺类固醇可以提高内侧基底下丘脑（MBH）的LHRH水平。然而，发作性LH释放与MBH - LHRH对17 -雌二醇的反应之间存在重要的分离。在目前的研究中，我们研究了不同剂量的睾酮(T)对MBH LHRH水平、发作性LH释放模式和垂体对LHRH的反应的影响；此外，我们还确定了引起MBH LHRH反应所需的T暴露时间。结果表明，低血清T浓度（413-638 pg/ml）与高浓度T浓度（1337-1776 pg/ml）在提高96 h MBH LHRH水平方面同样有效；然而，较高的T水平（大于1 ng/ml）抑制LH释放与LHRH水平升高同时发生，而低T浓度并没有改变LH释放与MBH LHRH升高同时发生。对偶发性LH分泌模式的分析表明，这些低浓度的T既没有改变每3小时每只大鼠的脉冲次数、脉冲幅度，也没有改变脉间间隔。另一方面，随着T浓度的增加，脉冲幅度呈剂量相关的下降，而发作性LH分泌的其他成分保持不变。尽管T对LH释放模式有不同的影响，但垂体对外源性LHRH的敏感性随着T水平的高低而降低。这些研究表明：1)T可以激活细胞内的神经分泌事件，这些事件参与了中隆起神经末梢LHRH供应的增加；2) T可以通过可能不抑制LHRH释放的机制刺激LHRH在MBH中的积累；3)较高的T水平不会改变LH脉冲频率，而只会降低脉冲幅度，这可能是由于每次神经发作时LHRH释放量的减少和垂体对LHRH的敏感性降低所致。
We have previously reported that in castrated male rats gonadal steroids can raise LHRH levels in the medial basal hypothalamus (MBH). However, there was an important dissociation between episodic LH release and the MBH LHRH response to 17 beta-estradiol. In the present study we have examined the effects of varying the dose of testosterone (T) on the MBH LHRH levels, episodic LH release pattern, and pituitary responsiveness to LHRH; in addition we have determined the duration of T exposure required to elicit the MBH LHRH response. Results show that low serum levels of T (413-638 pg/ml) were just as effective as higher concentrations (1337-1776 pg/ml) in raising the MBH LHRH levels at 96 h; the minimum duration of exposure to T was 72 h. However, whereas higher T levels (greater than 1 ng/ml) suppressed LH release coincident with elevated LHRH levels, low T concentrations did not alter LH release contemporaneous with the MBH LHRH elevations. Analysis of the episodic LH secretion pattern disclosed that these low concentrations of T changed neither the number of pulses per 3 h per rat, pulse amplitude, nor the interpulse interval. On the other hand, as T concentrations were increased, pulse amplitude fell in a dose-related manner while other components of episodic LH secretion remained unchanged. Despite these differential effects of T on the LH release pattern, pituitary sensitivity to exogenous LHRH was reduced by the low as well as high levels of T. These studies show that 1) T can activate those intracellular neurosecretory events that are involved in augmented LHRH supply to the nerve terminals in the median eminence; 2) T can stimulate LHRH accumulation in the MBH by mechanisms that may not involve inhibition of LHRH release; and 3) higher T levels do not alter LH pulse frequency but depress only the pulse amplitude that may result from decrements in the amounts of LHRH released with each neural episode and depressed pituitary sensitivity to LHRH.