Smith M A, Vale W W
Endocrinology. 1981 Mar;108(3):752-9. doi: 10.1210/endo-108-3-752.
Chronic exposure to gonadotropin-releasing hormone (GnRH) in vivo eventually results in a failure to maintain maximal gonadotropin secretion, suggesting a loss of pituitary responsiveness. To examine changes in pituitary sensitivity in vitro, we have developed a superfusion technique in which dissociated rat anterior pituitary cells are attached to Cytodex beads. In this system, continuous administration of 30 nM GnRH caused an initial 20-fold increase in LH and FSH secretion rates. However, hormone secretion declined rapidly, reaching basal levels within 12 h. Both the calcium ionophore A23187 and the cocarcinogen phorbol myristate acetate were effective in releasing additional LH and FSH from cells made refractory to 30 nM GnRH, whereas higher doses of GnRH and 8-bromo-cAMP were minimally active. A rapid loss of response was also seen with a superactive GnRH agonist but was not observed with a GnRH antagonist. Desensitization to prolonged superfusion with phorbol myristate acetate was also observed, although these cells remained sensitive to GnRH. In contrast to the development of tolerance produced by continuous exposure to GnRH, repeated delivery of GnRH in a pulsatile fashion maintained pituitary responsiveness for more than 24 h. A priming effect was observed for both LH and FSH. Such results demonstrate that continuous, but not intermittent, exposure to GnRH is capable of producing desensitization in superfused anterior pituitary cells.
体内长期暴露于促性腺激素释放激素（GnRH）最终会导致无法维持最大促性腺激素分泌，提示垂体反应性丧失。为了在体外检测垂体敏感性的变化，我们开发了一种灌流技术，即将解离的大鼠垂体前叶细胞附着于Cytodex微珠上。在该系统中，持续给予30 nM GnRH可使促黄体生成素（LH）和促卵泡生成素（FSH）分泌率最初增加20倍。然而，激素分泌迅速下降，在12小时内降至基础水平。钙离子载体A23187和促癌剂佛波醇肉豆蔻酸酯均可有效地从对30 nM GnRH产生不应性的细胞中释放出额外的LH和FSH，而更高剂量的GnRH和8-溴环磷腺苷（8-bromo-cAMP）的活性则极低。一种超活性GnRH激动剂也可导致反应迅速丧失，但GnRH拮抗剂则不会出现这种情况。尽管这些细胞对GnRH仍保持敏感，但对佛波醇肉豆蔻酸酯的长期灌流也会出现脱敏现象。与持续暴露于GnRH所产生的耐受性不同，以脉冲方式反复给予GnRH可使垂体反应性维持超过24小时。对LH和FSH均观察到了启动效应。这些结果表明，持续而非间歇性暴露于GnRH能够使灌流的垂体前叶细胞产生脱敏。
