Klemcke H G
U.S. Department of Agriculture, Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, NE.
Domest Anim Endocrinol. 1994 Jan;11(1):133-49. doi: 10.1016/0739-7240(94)90041-8.
Initial responses and adaptation of the porcine pituitary-adrenal axis to a chronic intermittent stressor (45-min daily restraint for 8 or 9 d) and effects of this stressor on binding to adrenocortical ACTH receptors were measured. Blood samples were obtained via indwelling jugular catheters on days 1, 5, and 9. On day 9, barrows (castrated male pigs; 40 kg) were killed and adrenal glands obtained. Binding to adrenal ACTH receptors was measured using [125I]Tyr23,Phe2,Nle4ACTH(1-38) analog. Basal (prestressor) ACTH, cortisol, and PRL concentrations were not affected by 9 d of 45-min restraint daily (RES-9). In RES-9 barrows, integrated ACTH responses to restraint decreased 46% (P < .05) between day 1 and day 5, then remained constant through day 9. Integrated PRL and cortisol responses were 28 to 30% lower on day 9 than on day 1 (P < .05). On day 9 integrated ACTH responses for RES-9 pigs were 59% lower than those of pigs exposed to a single 45-min restraint on day 9 (P < .05), whereas integrated cortisol responses were similar. Responsiveness of the pituitary-adrenal axis on day 9, 24 hr after the last of 8 daily 45-min restraints (RES-8), was compared with that of previously unstressed (naive) pigs. Exposure of RES-8 and naive pigs to a novel stressor (i.m. saline injection) produced plasma ACTH and cortisol responses of comparable magnitude. Intravenous injection of 2 micrograms ACTH (1-24) to RES-8 and naive pigs produced plasma cortisol responses of comparable magnitude. Plasma ACTH responses were 49% less (P < .05) in RES-8 pigs, and were associated with 65% increases (P = .02) of ACTH apparent metabolic clearance rates (ml/min/kg body weight), and 49% increases (P = .06) in ACTH apparent volumes of distribution (ml/kg body weight). In RES-8 pigs vs naive pigs, the ratio of integrated cortisol/integrated plasma ACTH was greater (P < .01) after ACTH injection, and the plasma cortisol response occurred more rapidly. Thus, RES-8 pigs appeared to be more responsive to ACTH. Since binding of ACTH to adrenocortical receptors did not differ between RES-8 or RES-9 pigs and controls, changes in ACTH receptors cannot account for differences in responsiveness. These data indicate chronic intermittent stressor-associated changes occur in functioning of the porcine pituitary-adrenal axis which are not apparent when considering only basal hormonal concentrations.
测定了猪垂体-肾上腺轴对慢性间歇性应激源（每天45分钟束缚，持续8或9天）的初始反应和适应性，以及该应激源对肾上腺皮质促肾上腺皮质激素（ACTH）受体结合的影响。在第1、5和9天通过留置颈静脉导管采集血样。在第9天，处死公猪（阉割雄性猪；40千克）并获取肾上腺。使用[125I]Tyr23、Phe2、Nle4ACTH(1 - 38)类似物测定肾上腺ACTH受体的结合情况。基础（应激前）ACTH、皮质醇和催乳素（PRL）浓度不受每天45分钟束缚9天（RES - 9）的影响。在RES - 9组公猪中，束缚刺激下ACTH的综合反应在第1天和第5天之间下降了46%（P < 0.05），然后在第9天保持稳定。PRL和皮质醇的综合反应在第9天比第1天低28%至30%（P < 0.05）。在第9天，RES - 9组猪的ACTH综合反应比第9天接受单次45分钟束缚的猪低59%（P < 0.05），而皮质醇综合反应相似。将每天8次45分钟束缚（RES - 8）的最后一次束缚后24小时的第9天垂体-肾上腺轴反应性与先前未受应激（未处理）的猪进行比较。RES - 8组和未处理组猪暴露于新的应激源（肌肉注射生理盐水）后，血浆ACTH和皮质醇反应幅度相当。对RES - 8组和未处理组猪静脉注射2微克ACTH(1 - 24)后，血浆皮质醇反应幅度相当。RES - 8组猪的血浆ACTH反应降低了49%（P < 0.05），且与ACTH表观代谢清除率（毫升/分钟/千克体重）增加65%（P = 0.02）以及ACTH表观分布容积（毫升/千克体重）增加49%（P = 0.06）相关。与未处理组猪相比，RES - 8组猪在注射ACTH后，皮质醇综合/血浆ACTH综合的比值更大（P < 0.01），且血浆皮质醇反应出现得更快。因此，RES - 8组猪似乎对ACTH更敏感。由于RES - 8组或RES - 9组猪与对照组之间ACTH与肾上腺皮质受体的结合没有差异，ACTH受体的变化不能解释反应性的差异。这些数据表明，猪垂体-肾上腺轴功能发生了与慢性间歇性应激源相关的变化，仅考虑基础激素浓度时这些变化并不明显。
