Szabo M, Frohman L A
Endocrinology. 1976 Jun;98(6):1451-9. doi: 10.1210/endo-98-6-1451.
The prolactin (PRL)-releasing activity of porcine stalk median eminence (pSME) was characterized by an in vivo bioassay and concomitant radioi-munoassay of plasma PRL and thyrotropin (TSH) levels. Methanol extracts of pSME stimulated PRL release in 3-day estrogen-primed rats when administered by the intracarotid route in doses ranging from 0.1 to 2.0 pSME equivalents. Synthetic thyrotropin-releasing hormone (TRH) stimulated the release of PRL and TSH in the dose range of 10 to 300 ng. PRL release was greater in response to a maximally effective dose of pSME than the release elicited by a maximal dose of TRH, and pSME administered together with a greater than mazimally effective dose of TRH caused additional PRL but not TSH secretion. Lysine vasopressin and prostaglandin E1 and E2 stimulated PRL release only at doses several orders of magnitude greater than the dose present in pSME. Somatostatin inhibited the release of TSH but not that of PRL whether the stimulus employed was pSME or TRH. The effective inhibitory dose of somatostatin was also significantly greater than the reported hypothalamic content. When pSME was subjected to incubation with plasma, a treatment reported to inactivate TRH, TSH-releasing activity was destroyed to a greater extent than was PRL-releasing activity. When pSME was adsorbed onto charcoal, the supernatant solution was devoid of TRH, as determined by complete removal of a [3H]TRH marker, yet substantial PRL-releasing activity was retained. TSH-releasing activity eluted from the charcoal with methanol was considerably greater than that expected on the basis of the recovery of [3H]TRH, suggesting the presence in the crude extract of a TSH-release inhibitor or of a TSH-releasing factor other than TRH. Based on the above evidence, we conclude that crude pSME contains PRL-releasing substance(s) distinct from the tripeptide TRH.
通过体内生物测定以及同时对血浆催乳素（PRL）和促甲状腺激素（TSH）水平进行放射免疫测定，对猪正中隆起（pSME）释放催乳素的活性进行了表征。当以0.1至2.0个pSME当量的剂量通过颈内途径给药时，pSME的甲醇提取物刺激了经3天雌激素预处理的大鼠体内PRL的释放。合成促甲状腺激素释放激素（TRH）在10至300 ng的剂量范围内刺激了PRL和TSH的释放。与最大剂量的TRH相比，对最大有效剂量的pSME产生的PRL释放更大，并且与大于最大有效剂量的TRH一起给药的pSME导致额外的PRL分泌，但不导致TSH分泌。赖氨酸加压素、前列腺素E1和E2仅在比pSME中存在的剂量大几个数量级的剂量下刺激PRL释放。无论刺激物是pSME还是TRH，生长抑素均抑制TSH的释放，但不抑制PRL的释放。生长抑素的有效抑制剂量也明显高于报道的下丘脑含量。当pSME与血浆一起孵育时（据报道这种处理会使TRH失活），TSH释放活性的破坏程度比PRL释放活性更大。当pSME吸附到活性炭上时，通过完全去除[3H]TRH标记物确定，上清液中不含TRH，但仍保留了大量的PRL释放活性。用甲醇从活性炭上洗脱的TSH释放活性明显高于基于[3H]TRH回收率预期的活性，这表明粗提取物中存在TSH释放抑制剂或除TRH之外的TSH释放因子。基于上述证据，我们得出结论，粗制pSME含有与三肽TRH不同的PRL释放物质。
