Ostrom K M
Department of Nutritional Sciences, University of Connecticut, Storrs.
Prog Food Nutr Sci. 1990;14(1):1-43.
The principal lactogenic hormone, prolactin, secreted by the anterior pituitary is critical to the establishment of lactation, milk macronutrient content and milk production. The concentration of circulating prolactin increases during pregnancy so that by the end of gestation, levels are 10 to 20 times over normal amounts. However, prolactin is prevented from exerting its effect on milk secretion by elevated levels of progesterone. Following clearance of progesterone and estrogen at parturition, copious milk secretion begins. The minimal hormonal requirements for normal lactation to occur are prolactin, insulin and hydrocortisone. Prolactin stabilizes and promotes transcription of casein mRNA; may stimulate synthesis of alpha-lactalbumin, the regulatory protein of the lactose synthetase enzyme system; and increases lipoprotein lipase activity in the mammary gland. Prolactin levels decrease as lactation is established but nursing stimulates prolactin release from the pituitary which promotes continued milk production. Prolactin is secreted into milk at levels representative of the average circulating concentration. The physiological significance of milk prolactin to the infant is uncertain. Prolactin exists in three heterogenic forms which possess varying biological activity. The monomer with a molecular weight of 23 kDa is found in greatest quantity and is the principal biologically active form. The pattern of heterogeneity changes during pregnancy to favor even more monomer in proportion to the dimer. However, during lactation, the proportion of the monomer in circulation decreases in response to selective uptake of the monomer by the mammary gland. Over 90 percent of the prolactin in milk is present as the monomer. Prolactin may exert some of its biological effect by a shift in the ratio of active to less active forms of the molecule.
垂体前叶分泌的主要催乳激素，即催乳素，对于泌乳的建立、乳汁常量营养素含量及产奶量至关重要。孕期循环催乳素浓度升高，至妊娠末期，其水平比正常量高出10至20倍。然而，孕酮水平升高会阻止催乳素对乳汁分泌发挥作用。分娩时孕酮和雌激素清除后，大量乳汁分泌开始。正常泌乳发生所需的最低激素为催乳素、胰岛素和氢化可的松。催乳素可稳定并促进酪蛋白mRNA的转录；可能刺激α-乳白蛋白（乳糖合成酶系统的调节蛋白）的合成；并增加乳腺中脂蛋白脂肪酶的活性。随着泌乳的建立，催乳素水平下降，但哺乳会刺激垂体释放催乳素，从而促进乳汁持续分泌。催乳素以代表平均循环浓度的水平分泌到乳汁中。乳汁中催乳素对婴儿的生理意义尚不确定。催乳素存在三种异源形式，具有不同的生物活性。分子量为23 kDa的单体含量最高，是主要的生物活性形式。孕期异质性模式发生变化，与二聚体相比，单体比例更高。然而，在泌乳期间，由于乳腺对单体的选择性摄取，循环中单体的比例会下降。乳汁中超过90%的催乳素以单体形式存在。催乳素可能通过分子中活性形式与活性较低形式比例的变化发挥其部分生物学效应。
