Fuchs A R, Cubile L, Dawood M Y, Jørgensen F S
Endocrinology. 1984 Feb;114(2):462-9. doi: 10.1210/endo-114-2-462.
Plasma oxytocin and PRL were measured in serial samples of blood collected from lactating rabbits nursing five to seven (mean, six) young on a once-daily suckling regimen. Each suckling episode lasted 4.0 +/- 1.1 (+/- SD) min on the average. Samples were obtained by means of an indwelling cardiac catheter before and 1, 3, 5, 10, 20, 30, and 60 min after suckling began. Measurements were performed at several stages of early, mid-, and late lactation. Oxytocin levels rose to peak values during suckling and declined rapidly after suckling stopped. PRL levels, on the other hand, did not reach peak values until 1-5 min after suckling had stopped, at which time plasma PRL concentrations plateaued and, in early and midlactation, were sustained at peak levels for 2-3 h; in late lactation, PRL secretion was not sustained after suckling had ceased. Peak PRL levels were relatively constant throughout most of lactation, with no significant differences between groups until late in lactation, when peak levels fell rather abruptly from a mean of 74 +/- 33.5 to 10.5 +/- 13.3 (+/- SD) ng/ml around day 25 in spite of a constant number of young and constant suckling frequency. Suckling failed to elicit any PRL release on day 30, but the administration of fluphenazine, a dopamine antagonist, did cause a rise in plasma PRL. Oxytocin release increased with advancing lactation, rising, on the average, 40 pg/ml on day 2 and to 250 and 490 pg/ml in mid- and late lactation, respectively. Dopaminergic agonist and antagonist drugs given to the doe before the nursing episode did not influence oxytocin release in response to suckling. Without a rise in plasma oxytocin, the young obtained no milk, but above a threshold level, there was no significant correlation between peak oxytocin levels and milk yield. When suckling failed to induce PRL secretion, milk secretion ceased rapidly in spite of copious oxytocin secretion. The failure of suckling to induce PRL release in late lactation, therefore, appears to be an important factor in the cessation of lactation.
在每日一次哺乳方案下，对哺育5至7只（平均6只）幼崽的泌乳兔采集的系列血样进行血浆催产素和催乳素测定。每次哺乳平均持续4.0±1.1（±标准差）分钟。在哺乳开始前以及开始后1、3、5、10、20、30和60分钟，通过留置心导管获取血样。在泌乳早期、中期和晚期的几个阶段进行测量。催产素水平在哺乳期间升至峰值，哺乳停止后迅速下降。另一方面，催乳素水平直到哺乳停止后1至5分钟才达到峰值，此时血浆催乳素浓度趋于平稳，在泌乳早期和中期，峰值水平持续2至3小时；在泌乳晚期，哺乳停止后催乳素分泌不再持续。在泌乳的大部分时间里，催乳素峰值水平相对恒定，各实验组之间直到泌乳后期才有显著差异，此时尽管幼崽数量和哺乳频率不变，但在第25天左右，峰值水平从平均74±33.5 ng/ml急剧降至10.5±13.3（±标准差）ng/ml。在第30天，哺乳未能引起任何催乳素释放，但给予多巴胺拮抗剂氟奋乃静确实导致血浆催乳素升高。催产素释放随着泌乳进展而增加，平均而言，在第2天升至40 pg/ml，在泌乳中期和晚期分别升至250和490 pg/ml。在哺乳前给母兔注射多巴胺能激动剂和拮抗剂药物，并不影响因哺乳引起的催产素释放。如果血浆催产素不升高，幼崽就得不到乳汁，但高于阈值水平时，催产素峰值水平与产奶量之间无显著相关性。当哺乳未能诱导催乳素分泌时，尽管催产素分泌大量增加，乳汁分泌仍迅速停止。因此，在泌乳后期哺乳未能诱导催乳素释放似乎是泌乳停止的一个重要因素。
