Rushen J, Nay T S, Wright L R, Payne D C, Foxcroft G R
Research Station, Agriculture Canada, Lennoxville, Québec.
Physiol Behav. 1995 Jul;58(1):43-8. doi: 10.1016/0031-9384(94)00375-f.
To determine the effect of stress on nursing, and the roles of HPA activity and opioid peptides, nine sows had their piglets removed for 2 h and were treated as follows: (a) control; (b) nose-snare restraint for 20 min; (c) naloxone injections (i.v. 2 mg/kg); and (d) snare + naloxone. After the treatment, the piglets were returned, milk ejections were timed, and the sows' blood sampled every 10 min for cortisol, growth hormone (GH), and prolactin assays. Piglet removal increased cortisol and decreased prolactin and GH. This was reversed when the piglets were returned. Restraint increased cortisol and decreased GH, but did not affect prolactin. Naloxone alone increased cortisol and decreased GH but did not increase the effect of restraint. The rise in GH following the piglets' return was abolished by the combination of restraint and naloxone. Neither restraint nor naloxone delayed the latency to first milk ejection or reduced the frequency. No unsuccessful nursings were observed. First milk ejections occurred when cortisol levels were elevated. Stress-induced activity of the hypothalamo-pituitary-adrenocortical (HPA) axis does not inhibit milk ejection in the pig, but this is not due to a protective opioid action. Endogenous opioids protect lactogenic hormones against inhibition by stress.
为了确定应激对哺乳的影响以及下丘脑-垂体-肾上腺（HPA）轴活动和阿片肽的作用，对9头母猪进行如下处理：将其仔猪拿走2小时，处理方式如下：（a）对照组；（b）用鼻圈套约束20分钟；（c）静脉注射纳洛酮（2毫克/千克）；（d）鼻圈套+纳洛酮。处理后，将仔猪放回，记录喷乳时间，并每隔10分钟采集母猪血液样本，用于检测皮质醇、生长激素（GH）和催乳素。拿走仔猪会使皮质醇升高，催乳素和GH降低。仔猪放回后这种情况会逆转。约束会使皮质醇升高，GH降低，但不影响催乳素。单独使用纳洛酮会使皮质醇升高，GH降低，但不会增强约束的效果。约束和纳洛酮联合使用会消除仔猪放回后GH的升高。约束和纳洛酮均未延迟首次喷乳的潜伏期或降低喷乳频率。未观察到不成功的哺乳情况。首次喷乳发生在皮质醇水平升高时。应激诱导的下丘脑-垂体-肾上腺皮质（HPA）轴活动不会抑制母猪的喷乳，但这并非由于阿片类物质的保护作用。内源性阿片肽可保护催乳激素免受应激的抑制。
