Biochemical aspects of the endometrium

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The distinctive biochemical properties of the endometrium are superimposed on a large number of properties and enzymatic capabilities that the endometrium shares with other tissues in the body. Endometrial cells have all of the enzymes to catalyze the glycolytic pathway, the pentose phosphate pathway, the β oxidation of fatty acids, oxidative phosphorylation, and the synthesis of glycogen, neutral fats, phospholipids, nucleic acids and proteins. Many of these enzymes undergo characteristic changes in activity correlated with the menstrual cycle and with pregnancy. The endometrium, like several other tissues, has specific, high affinity, low-capacity protein receptors which take up and bind estrogens noncovalently, together with other receptors that take up and bind progesterone. Prostaglandins, which have marked effects on uterine motility, also stimulate the synthesis of RNA when instilled into the lumen of the uterus. The synthesis of prostaglandins by human endometrium was demonstrated using endometrial explants grown in organ culture. Estradiol increased and progesterone decreased the synthesis of prostaglandin F 2α. The effects of estrogen appear to be mediated in large part by increased synthesis of RNA and protein, and of specific enzymes such as glucose-6-phosphate dehydrogenase and ornithine decarboxylase. The increase in protein and enzyme synthesis is evoked not only by the injection of estradiol, but by the instillation of RNA extracted from the uterus of an estrogen-treated animal. The RNA is purified by chromatography on a Sepharose polyuridylic acid column which binds only the RNA with a polyadenylic acid tail. Endometrium responds to estradiol in at least three independent fashions —by protein receptors which bind estradiol and transport it to the nucleus where it affects the genome producing RNA with specific information for the synthesis of specific enzymes, by an estrogen-dependent pyridine nucleotide transhydrogenase that mediates certain prompt metabolic effects, and by an effect on the synthesis or release of histamine which plays a role in the rapid appearance of hyperemia and water imbibition by endometrium.