Childs G V
Department of Anatomy and Neurosciences, University of Texas Medical Branch, Galveston.
Front Neuroendocrinol. 1992 Jul;13(3):271-317.
Investigators have described changes in pituitary corticotropes that correlate with changes in the physiological state of the animal. The stellate subtype degranulated and enlarged initially after adrenalectomy. This was followed by repopulation of the granules during the first 3 weeks after surgery with larger granules. There was also an increase in the percentage of corticotropes. More recent studies have shown that chronic stimulation with corticotropin-releasing hormone (CRH) produces some of the same changes; however, the magnitude differs because of corticosterone feedback. Corticotropes are heterogeneous in size, shape, storage patterns, and secretory responses. Specific changes are evident within a short time after stimulation as well. Their average cellular area increases within 1-2 h of stimulation by CRH in vitro or cold stress in vivo. Whereas many corticotropes acutely stimulated by cold or a novel environment are better granulated, others are depleted of granules. Cold stress for 30 min also stimulates an increase in the percentage of immunoreactive corticotropes and cells that bind CRH or arginine vasopressin (AVP). Secretagogues like CRH or epidermal growth factor (EGF) act in vitro to increase percentages of cells that store adrenocorticotropin (ACTH) or express mRNA for pro-opiomelanocortin. AVP or angiotensin II (A-II), or their activated second messengers, also increase percentages of cells that bind CRH and store ACTH. Inhibition of ACTH secretion by ion channel blockers or corticosterone has potent inhibitory effects on percentages of CRH-bound cells. AVP binding is not affected. Some of the inhibitory states reduce the average area of corticotropes. However, about 30% of the cells remain unaffected by these inhibitors. The rapid changes in cell percentages with the different treatments have led workers to postulate the existence of reserve cells that may be sensitive to certain levels of types of stimuli. Several candidate reserve cells are proposed. One group of cells that store ACTH with gonadotropins may function in the proestrous female to stimulate adrenal progesterone. Another multihormonal cell may function during cold stress to release both ACTH and thyroid-stimulating hormone (TSH) under the influence of AVP. There may be subpopulations of corticotropes that act in synchrony with other cell populations. They may be awaiting the proper type or combination of secretagogues to support the pituitary-adrenal and other axes.
研究人员已经描述了垂体促肾上腺皮质激素细胞的变化，这些变化与动物生理状态的变化相关。星状亚型在肾上腺切除术后最初会出现脱颗粒和细胞增大。随后，在手术后的前3周内，颗粒会重新填充，且颗粒更大。促肾上腺皮质激素细胞的百分比也有所增加。最近的研究表明，促肾上腺皮质激素释放激素（CRH）的慢性刺激会产生一些相同的变化；然而，由于皮质酮的反馈作用，变化程度有所不同。促肾上腺皮质激素细胞在大小、形状、储存模式和分泌反应方面存在异质性。刺激后短时间内也会出现特定变化。在体外经CRH刺激或体内经冷应激刺激1-2小时内，它们的平均细胞面积会增加。虽然许多因寒冷或新环境而受到急性刺激的促肾上腺皮质激素细胞颗粒更丰富，但其他细胞则颗粒减少。30分钟的冷应激还会刺激免疫反应性促肾上腺皮质激素细胞以及结合CRH或精氨酸加压素（AVP）的细胞百分比增加。像CRH或表皮生长因子（EGF）这样的促分泌素在体外作用可增加储存促肾上腺皮质激素（ACTH）或表达阿黑皮素原mRNA的细胞百分比。AVP或血管紧张素II（A-II），或它们激活的第二信使，也会增加结合CRH并储存ACTH的细胞百分比。离子通道阻滞剂或皮质酮对ACTH分泌的抑制对结合CRH的细胞百分比有强大的抑制作用。AVP结合不受影响。一些抑制状态会减小促肾上腺皮质激素细胞的平均面积。然而，约30%的细胞不受这些抑制剂的影响。不同处理导致的细胞百分比的快速变化使得研究人员推测可能存在对某些类型和水平的刺激敏感的储备细胞。提出了几种候选储备细胞。一组与促性腺激素一起储存ACTH的细胞可能在发情前期雌性动物中发挥作用，以刺激肾上腺孕酮的分泌。另一种多激素细胞可能在冷应激期间，在AVP的影响下释放ACTH和促甲状腺激素（TSH）。可能存在与其他细胞群体同步作用的促肾上腺皮质激素细胞亚群。它们可能在等待合适类型或组合的促分泌素来支持垂体-肾上腺轴和其他轴。
