Drouva S V, Rerat E, Leblanc P, Laplante E, Kordon C
Endocrinology. 1987 Aug;121(2):569-74. doi: 10.1210/endo-121-2-569.
We previously demonstrated a specific stimulatory action of estrogens on phosphatidylethanolamine methylation in rat pituitary membranes. To investigate the physiological relevancy of this effect, the activity of methylating enzyme(s) was evaluated during the rat estrous cycle, a period in which both endogenous ovarian steroid levels and the sensitivity of pituitary membrane receptors fluctuate. Anterior pituitary membranes (P2) were prepared from adult female rats at different stages of the estrous cycle and assayed for phospholipid methylation in the presence of S-adenosyl-[methyl-3H]methionine as a donor of 3H-methyl groups. Methylated phospholipids were separated by TLC. Formation of phosphatidyl-mono- and dimethylethanolamine and that of phosphatidylcholine increased significantly in the morning, reaching maximal values on the afternoon of proestrus; they decreased thereafter during estrus, metestrus, and diestrus. Plasma estradiol concentrations increased in late diestrus and then varied similarly with the fluctuations of phospholipid methyltransferase activity throughout the cycle. In parallel, plasma levels of LH and PRL were significantly elevated during the afternoon of proestrus, but remained low throughout the rest of the cycle. Under the same experimental conditions, phospholipid methylation in membranes prepared from mediobasal-hypothalamic structures was not affected. These data demonstrate that under physiological conditions the increased pituitary methyltransferase activity is associated with the progressive increment of plasma estradiol levels occurring shortly before proestrus and precedes the release of LH and PRL. Ovariectomy significantly decreased methyltransferase activity; however, 17 beta-estradiol treatment of ovariectomized rats for 5 days restored the enzyme activity, which was further augmented after progesterone administration. Attempting to investigate variations of pituitary methyltransferase activity in male rats, we demonstrated that the intact males showed weaker activity than that of females; orchidectomy diminished the phospholipid methylation, but adrenalectomy had no effect.
我们先前证明了雌激素对大鼠垂体膜中磷脂酰乙醇胺甲基化具有特定的刺激作用。为了研究这种作用的生理相关性，我们在大鼠发情周期中评估了甲基化酶的活性，在这个时期内，内源性卵巢类固醇水平和垂体膜受体的敏感性都会发生波动。从处于发情周期不同阶段的成年雌性大鼠制备垂体前叶膜（P2），并在存在作为3H-甲基供体的S-腺苷-[甲基-3H]甲硫氨酸的情况下测定磷脂甲基化。通过薄层层析分离甲基化的磷脂。磷脂酰单甲基乙醇胺和二甲基乙醇胺以及磷脂酰胆碱的形成在早晨显著增加，在动情前期下午达到最大值；此后在发情期、间情期和动情后期下降。血浆雌二醇浓度在动情后期末期升高，然后在整个周期中与磷脂甲基转移酶活性的波动相似地变化。同时，促黄体生成素（LH）和催乳素（PRL）的血浆水平在动情前期下午显著升高，但在周期的其余时间保持较低水平。在相同的实验条件下，从中基底部下丘脑结构制备的膜中的磷脂甲基化不受影响。这些数据表明，在生理条件下，垂体甲基转移酶活性的增加与动情前期前不久血浆雌二醇水平的逐渐升高相关，并且先于LH和PRL的释放。卵巢切除术显著降低了甲基转移酶活性；然而，对去卵巢大鼠进行5天的17β-雌二醇治疗可恢复酶活性，在给予孕酮后酶活性进一步增强。为了研究雄性大鼠垂体甲基转移酶活性的变化，我们证明完整雄性大鼠的活性比雌性大鼠弱；睾丸切除术减少了磷脂甲基化，但肾上腺切除术没有影响。
