Leiva L A, Croxatto H B
Instituto Chileno de Medicina Reproductiva, Santiago, Chile.
Biol Res. 1994;27(2):113-21.
Bovine median eminence contains a factor difference from gonadotropin-releasing hormone (GnRH) than increases basal luteinizing hormone (LH) secretion and potentiates GnRH-stimulated LH release. We compared the effect of hypothalamic neuropeptides on basal and GnRH-stimulated LH secretion using rat pituitary cells under static incubation conditions to determine if any of them mimics the LH-releasing activity no attributable to GnRH present in bovine median eminence extracts. Both, galanin and neurotensin (10(-9)-10(-5)) stimulated basal LH secretion in a dose-response manner. Galanin increased 3-4 fold and neurotensin doubled the basal LH secretion. The GnRH antagonist Nal-Glu 10(-6) M abolished the effect of 10(-7) M GnRH and 10(-5)M neurotensin, but did not block the LH-releasing activity of galanin. Leucin-enkephalin, beta-endorphin, substance P and neuropeptide Y (NPY) did not alter basal LH secretion. Neuropeptides produced three types of response on GnRH-stimulated LH release. First, leucine-enkephalin and beta-endorphin (10(-9)-10(-5) M) showed a dose-dependent inhibition of GnRH-stimulated LH release. At 10(-5) M the inhibition was complete with leucine-enkephalin and only 30% with beta-endorphin. Both were blocked by naloxone. Second, substance P showed an inverted U type response on GnRH-stimulated LH secretion. At 10(-9) M this peptide potentiated the action of GnRH. This effect decreased when the dose of substance P was increased to 10(-7) M and turned inhibitory at 10(-5) M when 10(-7) M GnRH was used. Third, galanin and NPY potentiated the effect of GnRH on LH secretion. Neurotensin had no effect on GnRH-stimulated LH release. In conclusion, rat gonadotrophs present diverse responses to neuropeptides at physiological concentrations, and -apart from GnRH-galanin is most likely the other factor present in bovine median eminence extracts that stimulates LH secretion. The data lend further support to a role of galanin in the control of LH secretion.
牛正中隆起含有一种不同于促性腺激素释放激素（GnRH）的因子，它能增加基础促黄体生成素（LH）的分泌，并增强GnRH刺激的LH释放。我们在静态孵育条件下，使用大鼠垂体细胞比较了下丘脑神经肽对基础和GnRH刺激的LH分泌的影响，以确定它们中是否有任何一种模拟了牛正中隆起提取物中存在的、并非由GnRH引起的LH释放活性。甘丙肽和神经降压素（10⁻⁹ - 10⁻⁵）均以剂量反应方式刺激基础LH分泌。甘丙肽使基础LH分泌增加3 - 4倍，神经降压素使其增加一倍。GnRH拮抗剂Nal - Glu（10⁻⁶ M）消除了10⁻⁷ M GnRH和10⁻⁵ M神经降压素的作用，但未阻断甘丙肽的LH释放活性。亮氨酸脑啡肽、β - 内啡肽、P物质和神经肽Y（NPY）均未改变基础LH分泌。神经肽对GnRH刺激的LH释放产生了三种类型的反应。第一，亮氨酸脑啡肽和β - 内啡肽（10⁻⁹ - 10⁻⁵ M）对GnRH刺激的LH释放表现出剂量依赖性抑制。在10⁻⁵ M时，亮氨酸脑啡肽的抑制作用完全，β - 内啡肽仅为30%。两者均被纳洛酮阻断。第二，P物质对GnRH刺激的LH分泌表现出倒U型反应。在10⁻⁹ M时，该肽增强了GnRH的作用。当P物质的剂量增加到10⁻⁷ M时，这种作用减弱，当使用10⁻⁷ M GnRH时，在10⁻⁵ M时变为抑制作用。第三，甘丙肽和NPY增强了GnRH对LH分泌的作用。神经降压素对GnRH刺激的LH释放无影响。总之，大鼠促性腺细胞在生理浓度下对神经肽呈现出多样的反应，并且除了GnRH外，甘丙肽很可能是牛正中隆起提取物中另一种刺激LH分泌的因子。这些数据进一步支持了甘丙肽在LH分泌控制中的作用。
