Lugo D I, Pintar J E
Department of Anatomy and Cell Biology, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA.
Dev Biol. 1996 Jan 10;173(1):95-109. doi: 10.1006/dbio.1996.0009.
Proopiomelanocortin (POMC)-producing cells are present in both the anterior (AL) and intermediate (IL) lobes of the adult rat pituitary. Both cell types are derived from a single embryonic rudiment, Rathke's pouch, and synthesize the same hormone precursor, POMC, but differ in the pattern of precursor processing and regulation of peptide secretion. Here we have used the reverse hemolytic plaque assay to determine the ontogeny of basal and regulated secretion by AL POMC cells. Basal secretion of beta-endorphin was first observed at Embryonic Day 13.5 (e13.5), the age when POMC-derived peptides were first detected immunocytochemically. Peptide secretion stimulated by corticotropin releasing hormone (CRH; 10(-8) M) was first detected at e15.5. The CRH-stimulated secretion involved two different components: (1) an increase in the amount of hormone secreted per cell (increase in plaque size) as well as (2) an increase in the number of plaque-producing cells. The greatest stimulation by CRH was observed at e16.5, a time when AL POMC mRNA levels increase significantly and when CRH neurons are first detected immunocytochemically in the hypothalamus. CRH-stimulated secretion, but not basal release, was inhibited by preincubation with dexamethasone (DEX; 10(-6) M) as early as e15.5, while the dopamine agonist ergocryptine (ERG; 10(-6) M) did not alter basal or CRH-stimulated release at any age studied. These results demonstrate that AL POMC cells are capable of hormone secretion as early as POMC peptides are first detected immunocytochemically and that these cells respond in an adult-like manner to physiological regulators soon after their initial appearance. Moreover, these responses remain unaltered during the early postnatal stress-nonresponsive period, suggesting that deficits at this time must lie at a level other than the corticotroph. Taken together, these results show that AL POMC cells possess functional regulatory receptor systems prior to maturation of the hypothalamic-hypophyseal portal system.
促阿黑皮素原（POMC）生成细胞存在于成年大鼠垂体的前叶（AL）和中间叶（IL）。这两种细胞类型均源自单一胚胎原基拉特克囊，且合成相同的激素前体POMC，但在前体加工模式和肽分泌调节方面存在差异。在此，我们使用反向溶血空斑试验来确定AL POMC细胞基础分泌和调节分泌的个体发生。在胚胎第13.5天（e13.5）首次观察到β-内啡肽的基础分泌，这也是免疫细胞化学首次检测到POMC衍生肽的年龄。促肾上腺皮质激素释放激素（CRH；10⁻⁸ M）刺激的肽分泌在e15.5首次检测到。CRH刺激的分泌涉及两个不同成分：（1）每个细胞分泌的激素量增加（空斑大小增加）以及（2）产生空斑的细胞数量增加。在e16.5观察到CRH的最大刺激作用，此时AL POMC mRNA水平显著增加，且下丘脑首次通过免疫细胞化学检测到CRH神经元。早在e15.5时，用 dexamethasone（DEX；10⁻⁶ M）预孵育可抑制CRH刺激的分泌，但不影响基础释放，而多巴胺激动剂麦角隐亭（ERG；10⁻⁶ M）在任何研究年龄均未改变基础或CRH刺激的释放。这些结果表明，早在免疫细胞化学首次检测到POMC肽时，AL POMC细胞就能够分泌激素，并且这些细胞在最初出现后不久就以类似成年的方式对生理调节因子作出反应。此外，在出生后早期应激无反应期，这些反应保持不变，这表明此时的缺陷必定存在于促肾上腺皮质激素细胞以外的水平。综上所述，这些结果表明，在下丘脑 - 垂体门脉系统成熟之前，AL POMC细胞就拥有功能性调节受体系统。
