Martí O, Armario A
Departament de Biologia Cellular i de Fisiologia, Facultat de Ciències, Universitat Autònoma de Barcelona, Bellaterra, Spain.
Int J Dev Neurosci. 1998 Jun-Jul;16(3-4):241-60. doi: 10.1016/s0736-5748(98)00030-6.
A wide array of physical and psychological stressors alter the secretion of anterior pituitary hormones. However, both the qualitative and the quantitative features of the stressors as well as its duration markedly influence the final endocrine response. In addition, among all anterior pituitary hormones, only ACTH and prolactin levels appear to reflect the intensity of the stress experienced by the animals. Although physical stressors show a somewhat specific neuroendocrine profile, the response of the pituitary-adrenal (PA) and sympathomedulloadrenal axes are common to almost all stressors. After an initial stimulatory effect of stress, an inhibition of all anterior pituitary hormones, except ACTH, can be found provided the stressor is intense enough. The mechanisms responsible for this biphasic response to stress are likely to be located at sites above the pituitary. When the animals are repeatedly exposed to the same stressor, some behavioural and physiological consequences of stress exposure are reduced, suggesting that the animals become adapted to the stimulus. This process has been also termed habituation. Among all the pituitary hormones, only ACTH and prolactin levels are reduced as a consequence of repeated exposure to the same (homotypic) stressor, although some negative results have been reported. However, it has been recently reported that subtle changes in the characteristics of the stressors or in their regularity can greatly influence adaptation, and these factors might explain failure to find adaptation of ACTH and prolactin in some works. Habituation of ACTH and prolactin, when observed, appears to be specific for the chronically applied stressor so that the potentiality of the PA axis and prolactin to respond to a novel (heterotypic) stressor can be preserved. In the case of the PA axis, an intact or potentiated response to a novel stressor is observed in spite of presumably negative feedback exerted by daily stress-induced glucocorticoid release and the high resting levels of glucocorticoids. This phenomenon has been termed as facilitation and can be unmasked alternating stress. Although with the exception of the PA axis, developmental aspects of anterior pituitary response to stress have been poorly studied, available data suggest that dramatic changes occur in some hormones during weaning, with some, but less profound, change thereafter. Responsiveness to stressors appears to mature with age, but developmental patterns differ among the various anterior pituitary hormones.
多种生理和心理应激源会改变垂体前叶激素的分泌。然而，应激源的性质和数量及其持续时间都会显著影响最终的内分泌反应。此外，在所有垂体前叶激素中，似乎只有促肾上腺皮质激素（ACTH）和催乳素水平能反映动物所经历应激的强度。虽然生理应激源呈现出某种特定的神经内分泌特征，但垂体 - 肾上腺（PA）轴和交感 - 肾上腺髓质轴的反应几乎对所有应激源都是常见的。在应激产生初始刺激作用后，如果应激源强度足够，除ACTH外，所有垂体前叶激素的分泌都会受到抑制。对应激这种双相反应的机制可能位于垂体上方的部位。当动物反复暴露于同一应激源时，应激暴露的一些行为和生理后果会减轻，这表明动物对该刺激产生了适应。这个过程也被称为习惯化。在所有垂体激素中，尽管有一些负面报道，但只有ACTH和催乳素水平会因反复暴露于同一（同型）应激源而降低。然而，最近有报道称，应激源特征或其规律性的细微变化会极大地影响适应，这些因素可能解释了在一些研究中未能发现ACTH和催乳素适应现象的原因。当观察到ACTH和催乳素的习惯化时，似乎对长期应用的应激源具有特异性，从而可以保留PA轴和催乳素对新的（异型）应激源作出反应的潜力。就PA轴而言，尽管日常应激诱导的糖皮质激素释放可能产生负反馈以及糖皮质激素的高基础水平，但对新应激源仍会观察到完整或增强的反应。这种现象被称为易化作用，并且可以通过交替应激来揭示。虽然除PA轴外，垂体前叶对应激反应的发育方面研究较少，但现有数据表明，在断奶期间某些激素会发生显著变化，此后也会有一些但不太明显的变化。对应激源的反应性似乎会随着年龄增长而成熟，但不同垂体前叶激素的发育模式有所不同。
