Akana S F, Strack A M, Hanson E S, Dallman M F
Department of Physiology, University of California, San Francisco 94143-0444.
Endocrinology. 1994 Sep;135(3):1125-34. doi: 10.1210/endo.135.3.8070356.
We have previously reported that there are diurnal rhythms in the magnitude of ACTH responses to stressors and in the sensitivity of stress-induced ACTH responses to facilitation induced by prior stress and to corticosterone (B) feedback induced by exogenous B. In all cases ACTH was more responsive in the morning than in the evening in nocturnally feeding rats. We have also shown in adrenalectomized rats that an overnight fast reduces ACTH responses to restraint in the morning compared with rats fed ad libitum, and we have shown that calorie-containing gavage during the fast increases the amplitude of ACTH responses to restraint in fasted rats. Therefore, this diurnal rhythm is not associated with B feedback and is associated with calories. In these studies we asked whether young, male intact rats that were deprived of food overnight had: 1) hypothalamo-pituitary-adrenal (HPA) axis responses during the fasting period; 2) altered basal activity in the HPA axis; 3) altered responsivity of ACTH to restraint; and 4) altered sensitivity of restraint-induced ACTH responses to facilitation or B feedback. Our results show that food deprivation: 1) induces marked ACTH and B responses during the fast that mirrors the pattern of food intake in fed rats, with an approximately 3-h lag; 2) results in essentially no change in basal ACTH in the morning; 3) reduces ACTH responsivity to stress in the morning; and 4) reduces ACTH responsivity to prior stress-induced facilitation and exogenous B-induced feedback. We conclude that: 1) the HPA axis serves as a default pathway to feeding when food is not available; 2) the diurnal rhythms in restraint-induced ACTH secretion are determined by food intake; and 3) the HPA axis is integral to a larger hypothalamic system that mediates energy flow.
我们之前曾报道，促肾上腺皮质激素（ACTH）对应激源的反应强度以及应激诱导的ACTH反应对应激预处理诱导的促进作用和外源性皮质酮（B）反馈的敏感性存在昼夜节律。在所有情况下，夜行性进食大鼠的ACTH在早晨比晚上反应更强。我们还在肾上腺切除的大鼠中发现，与随意进食的大鼠相比，禁食一夜会降低早晨ACTH对束缚的反应，并且我们已经表明，禁食期间给予含热量的灌胃会增加禁食大鼠ACTH对束缚的反应幅度。因此，这种昼夜节律与B反馈无关，而是与热量有关。在这些研究中，我们询问了一夜未进食的年轻雄性未阉割大鼠是否：1）在禁食期间下丘脑-垂体-肾上腺（HPA）轴有反应；2）HPA轴的基础活性发生改变；3）ACTH对束缚的反应性发生改变；4）束缚诱导的ACTH反应对促进作用或B反馈的敏感性发生改变。我们的结果表明，食物剥夺：1）在禁食期间诱导显著的ACTH和B反应，这与进食大鼠的食物摄入模式相似，但有大约3小时的延迟；2）导致早晨基础ACTH基本没有变化；3）降低早晨ACTH对应激的反应性；4）降低ACTH对先前应激诱导的促进作用和外源性B诱导的反馈的反应性。我们得出结论：1）当没有食物时，HPA轴作为进食的默认途径；2）束缚诱导的ACTH分泌的昼夜节律由食物摄入决定；3）HPA轴是介导能量流动的更大下丘脑系统的组成部分。
