Hubbard G M, Licht P
Gen Comp Endocrinol. 1986 Mar;61(3):417-23. doi: 10.1016/0016-6480(86)90227-3.
An in vitro superfusion system was used to study the relative effects of pulsatile and continuous gonadotrophin administration on steroid secretion and oocyte maturation in Rana pipiens ovaries. Pulsatile (10 min pulse/hr) delivery of pituitary extract (PE) resulted in a slightly (insignificantly) lower level of testosterone (T) secretion over a 12-hr period. Administration of a fivefold lower, subliminal amount of PE instead of hormone-free media between pulses did not change the pattern of T secretion. When the interpulse frequency was increased to 2 or 3 hr, there were notable oscillations in T secretion which corresponded to the peaks in luteinizing hormone associated with the PE. In four experiments ovarian fragments underwent oocyte maturation, but this occurred only in fragments that received continuous PE stimulation. Progesterone (P) secretion was measurable only when oocyte maturation was observed in the ovarian fragment. Rana catesbeiana ovarian fragments exposed to continuous superfusion with homologous PE produced more T than those receiving hourly pulses of PE over a 6-hr period. Oocyte maturation accompanied by P secretion was observed in one experiment under continuous, but not pulsatile administration of PE. These results suggest that the frog ovary may be more resistant than the mammalian ovary to "down-regulation" under continuous gonadotrophic stimulation. The implications of these results on the frog pituitary--gonadal axis are discussed.
采用体外灌流系统研究了脉冲式和持续性给予促性腺激素对牛蛙卵巢类固醇分泌和卵母细胞成熟的相对影响。垂体提取物（PE）以脉冲式（每小时10分钟脉冲）给药，在12小时内睾酮（T）分泌水平略有（不显著）降低。在脉冲之间给予五分之一剂量的阈下PE而非无激素培养基，并未改变T的分泌模式。当脉冲间期增加到2或3小时时，T分泌出现明显振荡，这与与PE相关的促黄体生成素峰值相对应。在四项实验中，卵巢碎片经历了卵母细胞成熟，但这仅发生在接受持续性PE刺激的碎片中。只有在卵巢碎片中观察到卵母细胞成熟时，才能检测到孕酮（P）分泌。在6小时内，暴露于同源PE持续灌流的牛蛙卵巢碎片比接受每小时一次PE脉冲的碎片产生更多的T。在一项实验中，在持续性而非脉冲式给予PE的情况下，观察到伴有P分泌的卵母细胞成熟。这些结果表明，在持续性促性腺激素刺激下，蛙卵巢可能比哺乳动物卵巢更不易受到“下调”影响。本文讨论了这些结果对蛙垂体-性腺轴的意义。
