Liu R C, Lea R W, Sharp P J
Department of Applied Biology, University of Central Lancashire, Preston, United Kingdom.
Gen Comp Endocrinol. 1995 Dec;100(3):267-72. doi: 10.1006/gcen.1995.1157.
Continuous perifusion of quartered anterior pituitary glands from juvenile and adult chickens of both sexes with chicken gonadotrophin-releasing hormone-I (cGnRH-I) stimulated a spike-plateau profile of luteinizing hormone (LH) secretion. When perifused in Ca(2+)-free medium, pituitary glands from juveniles of both sexes and from adult cockerels but not those from laying hens, released LH in response to cGnRH-I. This release occurred at the same time as the spike phase of the response seen in the presence of extracellular Ca2+ and was not accompanied by a plateau phase of secretion. The magnitude of the plateau but not the spike phase of LH secretion from pituitary glands from adult males and females was reduced by the L-type Ca2+ channel blocker, nifedipine. This suggests that the mechanism of cGnRH-I-induced LH release from pituitary glands from laying hens is independent of mobilization of intracellular Ca2+, and that entry of Ca2+ during the spike phase of LH secretion occurs through non-L-type Ca2+ channels. Both non-L-type and L-type Ca2+ channels operate during the plateau phase of secretion in adults of both sexes. The duration of the spike phase of LH release from pituitary glands from adult cockerels was curtailed in the presence of nifedipine. The spike phase of LH release from the adult cockerel pituitary therefore involves three modes of Ca2+ flux, comprising an intracellular Ca(2+)-dependent component and extracellular components involving Ca2+ entry through L-type and non-L-type Ca2+ channels. The finding that the extracellular Ca(2+)-independent component of cGnRH-I-stimulated LH release from pituitary glands from juvenile hens is not present in adult hens suggests that this difference is related to sexual maturation. The maturational and sexual differences in the LH response to cGnRH-I could be mediated through the high concentrations of plasma 17 beta-oestradiol in adult hens which suppress the mobilization of intracellular stores of Ca2+ in the gonadotrophes.
用鸡促性腺激素释放激素-I（cGnRH-I）持续灌流来自幼年和成年两性鸡的四分前脑垂体，可刺激促黄体生成素（LH）分泌呈现峰-平台模式。当在无钙培养基中灌流时，两性幼年鸡和成年公鸡的垂体可对cGnRH-I作出反应释放LH，但产蛋母鸡的垂体则不然。这种释放在细胞外钙存在时所见反应的峰期同时发生，且不伴有分泌的平台期。成年雄性和雌性垂体LH分泌的平台期而非峰期的幅度，被L型钙通道阻滞剂硝苯地平降低。这表明cGnRH-I诱导产蛋母鸡垂体释放LH的机制与细胞内钙的动员无关，且LH分泌峰期钙的进入是通过非L型钙通道。在两性成年鸡分泌的平台期，非L型和L型钙通道均起作用。在硝苯地平存在的情况下，成年公鸡垂体LH释放峰期的持续时间缩短。因此，成年公鸡垂体LH释放的峰期涉及三种钙通量模式，包括细胞内钙依赖性成分和涉及通过L型和非L型钙通道进入钙的细胞外成分。幼年母鸡垂体cGnRH-I刺激的LH释放中细胞外钙非依赖性成分在成年母鸡中不存在这一发现表明，这种差异与性成熟有关。LH对cGnRH-I反应的成熟和性别差异可能是通过成年母鸡血浆中高浓度的17β-雌二醇介导的，其抑制促性腺细胞中细胞内钙储存的动员。
