Briski K P, Swanson G N, Sylvester P W
Department of Veterinary and Comparative Anatomy, Pharmacology, and Physiology, College of Veterinary Medicine, Washington State University, Pullman 99164-6520, USA.
Neuroendocrinology. 1996 May;63(5):437-45. doi: 10.1159/000127069.
Although pituitary prolactin (PRL) exhibits size and charge variability, questions concerning the structural heterogeneity and biological potency of hormonal forms secreted in vivo remain. In the present studies, monomeric PRL in male rat pituitaries and plasma was fractionated by Sephacryl S-100 size exclusion chromatography and aqueous chromatofocusing to resolve size and charge forms under conditions compatible with optimum preservation of biological activity. Individual hormonal variants were subsequently evaluated for their ability to stimulate the growth of PRL receptor-bearing rat lymphoma cells in vitro. Pituitary elution profiles contained several cross-reactive size variants ranging from 30.4 to 21.5 kD in M(r); major hormonal peaks were eluted at 25.6, 24.3, and 23.6 kD. Multiple size forms of PRL were also detected in plasma profiles, with predominant peaks eluting between 26.5 and 21.5 kD M(r) in size. Mean B/I ratios, established as an index of relative biopotency, varied significantly between size variants obtained from pituitary and plasma. Pituitary PRL size variants of 27.1, 24.3, and 21.5 kD exhibited greatest potency in the in vitro bioassay, whereas the 25.6- and 23.6-kD forms were least potent under these conditions. Of the PRL size variants detected in peripheral plasma, those of 24.3 and 21.5 kD size were characterized by highest mean B/I ratios. Pituitary 24.3-kD PRL was chromatofocused as five charge variants of pI 5.34, 5.31, 5.26, 5.20, and 5.14; only some of these isomers are apparently secreted in vivo, since pI values for plasma charge isomers ranged from 5.26 to 5.14. Charge isomers of pituitary 24.3-kD PRL exerted variable mitogenicity in the Nb2 in vitro bioassay. The highest mean B/I ratio was associated with the relatively basic 24.3-kD isomer of pI 5.31; the relative biopotency of more acidic charge isomers was progressively diminished with increasing acidic charge. In summary, the present findings show that both size and charge variants of male rat pituitary PRL exhibit differential biopotency in vitro, indicative of their functional heterogeneity. The demonstration of multiple hormonal forms in peripheral plasma suggests that the net biopotency of circulating PRL reflects the sum of activity of structurally and functionally diverse molecules.
尽管垂体催乳素（PRL）存在大小和电荷的变异性，但关于体内分泌的激素形式的结构异质性和生物活性的问题仍然存在。在本研究中，通过Sephacryl S - 100尺寸排阻色谱法和水性色谱聚焦法对雄性大鼠垂体和血浆中的单体PRL进行分级分离，以在与生物活性最佳保存相容的条件下解析大小和电荷形式。随后评估各个激素变体在体外刺激携带PRL受体的大鼠淋巴瘤细胞生长的能力。垂体洗脱图谱包含几种交叉反应性大小变体，其相对分子质量（M(r)）范围为30.4至21.5 kD；主要激素峰在25.6、24.3和23.6 kD处洗脱。在血浆图谱中也检测到多种大小形式的PRL，主要峰在大小为26.5至21.5 kD M(r)之间洗脱。作为相对生物活性指标建立的平均B/I比值，在从垂体和血浆获得的大小变体之间有显著差异。27.1、24.3和21.5 kD的垂体PRL大小变体在体外生物测定中表现出最大的活性，而在这些条件下25.6 - kD和23.6 - kD形式活性最低。在外周血浆中检测到的PRL大小变体中，24.3和21.5 kD大小的变体具有最高的平均B/I比值。垂体24.3 - kD PRL通过色谱聚焦分离为pI为5.34、5.31、5.26、5.20和5.14的五个电荷变体；这些异构体中只有一些显然在体内分泌，因为血浆电荷异构体的pI值范围为5.26至5.14。垂体24.3 - kD PRL的电荷异构体在Nb2体外生物测定中表现出不同的促有丝分裂活性。最高的平均B/I比值与相对碱性的pI 5.31的24.3 - kD异构体相关；酸性更强的电荷异构体的相对生物活性随着酸性电荷的增加而逐渐降低。总之，本研究结果表明，雄性大鼠垂体PRL的大小和电荷变体在体外均表现出不同的生物活性，表明它们的功能异质性。外周血浆中多种激素形式的证明表明，循环PRL的净生物活性反映了结构和功能多样的分子活性的总和。
