Jarvis S, Lawrence A B, McLean K A, Chirnside J, Deans L A, Calvert S K
Animal Biology Division, SAC Edinburgh, Midlothian, UK.
Anim Reprod Sci. 1998 Aug 21;52(2):139-51. doi: 10.1016/s0378-4320(98)00090-6.
Previous work has indicated that plasma cortisol increases during farrowing in the pig suggesting increasing physiological stress. The aim of this study was to determine changes in plasma cortisol and beta-endorphin over farrowing in the pig to obtain a more detailed profile of pituitary and adrenal release at this time and also to investigate the involvement of endogenous opioids in the mediation of the HPA axis. Indwelling jugular catheters were implanted, under general anaesthesia, in 31 Large White x Landrace gilts approximately 15 days before the expected parturition day (EPD). Gilts were moved into either a farrowing crate, without straw (n = 15), or a straw-bedded pen (n = 16) 5 days before the EPD. Samples were taken during the pre-farrowing period and then during farrowing itself. At 7.5 min after the birth of the first piglet (BFP), gilts either received naloxone, an opioid antagonist, (1 mg kg(-1) body weight, i.v.) or a control dose of saline. Plasma beta-endorphin increased following the BFP but remained fairly constant over the third and fourth hour of farrowing. Plasma cortisol continued to increase over the 4 h following the BFP. Changes seen in these hormones were generally insensitive to the environment and there was little evidence of opioid mediation of the HPA axis at parturition. From these results it is suggested that certain aspect(s) of parturition itself stimulate the HPA axis. However it is unknown if the rise in plasma cortisol is a result of some stress-inducing factor of the parturition process or whether it reflects a metabolic function. The study also demonstrates the lack of any inhibitory mediation of the HPA axis by endogenous opioids at parturition.
先前的研究表明，母猪分娩期间血浆皮质醇水平会升高，这表明生理应激在增加。本研究的目的是确定母猪分娩过程中血浆皮质醇和β-内啡肽的变化，以便更详细地了解此时垂体和肾上腺的释放情况，并研究内源性阿片类物质在介导下丘脑-垂体-肾上腺（HPA）轴中的作用。在全身麻醉下，于预计分娩日（EPD）前约15天，为31头大白猪×长白猪杂交后备母猪植入颈静脉留置导管。在EPD前5天，将母猪转移至无垫草的分娩栏（n = 15）或有垫草的围栏（n = 16）中。在分娩前阶段以及分娩过程中采集样本。在第一头仔猪出生后7.5分钟（BFP），给母猪静脉注射阿片类拮抗剂纳洛酮（1 mg kg⁻¹体重）或对照剂量的生理盐水。BFP后血浆β-内啡肽升高，但在分娩的第三和第四小时保持相当稳定。BFP后的4小时内，血浆皮质醇持续升高。这些激素的变化通常对环境不敏感，并且几乎没有证据表明分娩时内源性阿片类物质对HPA轴有介导作用。从这些结果可以推测，分娩本身的某些方面会刺激HPA轴。然而，尚不清楚血浆皮质醇的升高是分娩过程中某些应激诱导因素的结果，还是反映了一种代谢功能。该研究还表明，分娩时内源性阿片类物质对HPA轴缺乏任何抑制性介导作用。
