Judd A M, MacLeod R M
Department of Internal Medicine, University of Virginia Health Sciences Center, Charlottesville 22908.
Endocrinology. 1992 Sep;131(3):1251-60. doi: 10.1210/endo.131.3.1505463.
TRH and lysine-bradykinin (Lys-bradykinin) increase PRL release and arachidonate liberation from anterior pituitary cells. We investigated whether the arachidonate liberation stimulated by TRH and Lys-bradykinin originates in pituitary lactotropes and whether these events are accomplished through similar mechanisms. Lys-bradykinin and TRH rapidly (0.5 min) increased the intracellular [3H]arachidonate content of rat anterior pituitary cells. Lys-bradykinin also increased [3H]arachidonate liberation and PRL release from lactotrope-enriched pituitary cells, but not from a pituitary cell preparation with a diminished number of lactotropes. In contrast, TRH increased [3H]arachidonate liberation from both lactotrope-enriched and lactotrope-diminished preparations; this increased [3H]arachidonate liberation stimulated by TRH in the lactotrope-diminished cells may originate in the thyrotropes. The effects of TRH and Lys-bradykinin on [3H]arachidonate and [14C]stearate liberation in perfused pituitary cells also were determined. Both secretagogues increased arachidonate and stearate liberation in a biphasic manner, characterized by a transient spike, followed by a lower magnitude wave of fatty acid release. The spike phase produced by Lys-bradykinin was more pronounced than that produced by TRH. The calcium dependence of TRH- and Lys-bradykinin-stimulated arachidonate liberation also was investigated. Cobalt and the low calcium medium containing ionomycin were used to block the secretagogue-induced increase in intracellular calcium concentrations. These conditions blocked TRH-stimulated arachidonate liberation, but only marginally decreased Lys-bradykinin-stimulated arachidonate liberation, indicating that the two peptides act through different mechanisms. Therefore, TRH stimulation of arachidonate liberation is linked to an increase in intracellular calcium. In contrast, Lys-bradykinin increases arachidonate liberation through a calcium-independent intracellular mediator. This calcium-independent increase in arachidonate liberation may involve the bradykinin receptor being coupled directly to a phospholipase, a G-protein that provides a link between the bradykinin receptor and the phospholipases that liberate arachidonate, or bradykinin-induced activation of a protein kinase-C that activates the phospholipases and subsequently liberates arachidonate.
促甲状腺激素释放激素（TRH）和赖氨酸缓激肽可增加垂体前叶细胞催乳素的释放及花生四烯酸的释放。我们研究了TRH和赖氨酸缓激肽刺激产生的花生四烯酸释放是否源于垂体催乳细胞，以及这些过程是否通过相似机制完成。赖氨酸缓激肽和TRH迅速（0.5分钟）增加大鼠垂体前叶细胞内的[3H]花生四烯酸含量。赖氨酸缓激肽还可增加富含催乳细胞的垂体细胞中[3H]花生四烯酸的释放及催乳素的释放，但对催乳细胞数量减少的垂体细胞制剂则无此作用。相反，TRH可增加富含催乳细胞和催乳细胞减少的制剂中[3H]花生四烯酸的释放；TRH在催乳细胞减少的细胞中刺激产生的[3H]花生四烯酸释放增加可能源于促甲状腺细胞。还测定了TRH和赖氨酸缓激肽对灌流垂体细胞中[3H]花生四烯酸和[14C]硬脂酸释放的影响。两种促分泌素均以双相方式增加花生四烯酸和硬脂酸的释放，其特点是出现短暂峰值，随后是幅度较低的脂肪酸释放波。赖氨酸缓激肽产生的峰值阶段比TRH产生的更明显。还研究了TRH和赖氨酸缓激肽刺激的花生四烯酸释放对钙的依赖性。使用钴和含离子霉素的低钙培养基来阻断促分泌素诱导的细胞内钙浓度升高。这些条件阻断了TRH刺激的花生四烯酸释放，但仅轻微降低了赖氨酸缓激肽刺激的花生四烯酸释放，表明这两种肽通过不同机制起作用。因此，TRH刺激花生四烯酸释放与细胞内钙增加有关。相反，赖氨酸缓激肽通过不依赖钙的细胞内介质增加花生四烯酸释放。这种不依赖钙的花生四烯酸释放增加可能涉及缓激肽受体直接与磷脂酶偶联、一种在缓激肽受体和释放花生四烯酸的磷脂酶之间起连接作用的G蛋白，或缓激肽诱导的蛋白激酶-C激活，该激活作用激活磷脂酶并随后释放花生四烯酸。
