Liu T C, Jackson G L
Endocrinology. 1984 Aug;115(2):605-13. doi: 10.1210/endo-115-2-605.
We investigated the temporal release of LH by rat pituitary cells superfused with repeated pulses of GnRH at different doses (amplitudes), frequencies, and pulse durations. Anterior pituitary (AP) cells prepared from ovariectomized rats were cultured on bio-beads and then placed in columns and superfused. The cells were stimulated intermittently for 24 h with synthetic GnRH given as pulses of 6-, 10-, or 15-min duration at frequencies of one pulse per 30, 60, or 90 min. In the first experiment we tested the temporal response of cells exposed to different doses of GnRH. At all doses, the first pulse of GnRH stimulated greater LH release than subsequent pulses. The response to subsequent pulses varied with dose. At low doses (1 and 5 X 10(-10)M) of GnRH, the AP cells stabilized and released similar amounts of LH in response to each sequential identical GnRH pulse for up to 24 h. In contrast, at high doses (10(-8) and 10(-6)M) of GnRH, the AP cells gradually released less LH with each pulse. During the initial pulses, the dose-response curves of LH release were linear between doses of 5 X 10(-10) to 1 X 10(-6) M GnRH. Thereafter, the maximum response was diminished, and the slope of the dose-response curve was reduced. In subsequent experiments we found that the decline in responsiveness with time was not due to either degradation of GnRH in the medium or loss of cell viability. The low responsiveness to high GnRH pulses at the end of the superfusion period could be overcome temporarily by further increasing the dose of GnRH. In the presence of high doses, changing GnRH pulse frequency from one 6-min pulse per h to one 6-min pulse per 1.5 h or changing duration from one repeated 10-min pulse per h to one repeated 6-min pulse per h had no detectable effect on the temporal pattern of LH release. These results suggest that, similar to constant infusion, pulsatile delivery of GnRH at high doses to AP cells can induce cell refractoriness to GnRH. This loss of responsiveness probably involves factors in addition to depletion of GnRH receptors and the releasable LH pool. In contrast, pulsatile delivery of low doses of GnRH appears to maintain LH release at a relatively constant level for up to 24 h.
我们研究了用不同剂量（幅度）、频率和脉冲持续时间的GnRH重复脉冲对大鼠垂体细胞进行灌流时LH的瞬时释放情况。从去卵巢大鼠制备的垂体前叶（AP）细胞在生物珠上培养，然后置于柱中进行灌流。用合成GnRH以6分钟、10分钟或15分钟的脉冲持续时间，每30分钟、60分钟或90分钟一个脉冲的频率间歇性刺激细胞24小时。在第一个实验中，我们测试了暴露于不同剂量GnRH的细胞的瞬时反应。在所有剂量下，GnRH的第一个脉冲刺激的LH释放量都比后续脉冲大。对后续脉冲的反应随剂量而变化。在低剂量（1和5×10⁻¹⁰M）的GnRH下，AP细胞稳定下来，并在长达24小时内对每个连续相同的GnRH脉冲释放相似量的LH。相反，在高剂量（10⁻⁸和10⁻⁶M）的GnRH下，AP细胞随着每个脉冲逐渐释放较少的LH。在最初的脉冲期间，LH释放的剂量反应曲线在5×10⁻¹⁰至1×10⁻⁶M GnRH剂量之间呈线性。此后，最大反应减弱，剂量反应曲线的斜率降低。在后续实验中，我们发现反应性随时间下降不是由于培养基中GnRH的降解或细胞活力的丧失。在灌流期结束时对高GnRH脉冲的低反应性可以通过进一步增加GnRH剂量暂时克服。在高剂量存在的情况下，将GnRH脉冲频率从每小时一个6分钟脉冲改为每1.5小时一个6分钟脉冲，或将持续时间从每小时一个重复的10分钟脉冲改为每小时一个重复的6分钟脉冲，对LH释放的瞬时模式没有可检测到的影响。这些结果表明，与持续输注类似，高剂量的GnRH脉冲式输送到AP细胞可诱导细胞对GnRH产生不应性。这种反应性的丧失可能涉及除GnRH受体耗竭和可释放的LH池之外的因素。相反，低剂量的GnRH脉冲式输送似乎能使LH释放在长达24小时内维持在相对恒定的水平。
