Progesterone

Progesterone (P) is a 21C steroid hormone, which is converted from cholesterol via pregnenolone by isomerase. In non-pregnant women, P is produced by follicular membrane cells in the ovary. During pregnancy, P is mainly secreted by the placental syncytiotrophoblast layer, so the level of P in blood is mainly related to the weight of the placenta and the amount of blood perfusion. It rises slowly in the first trimester, and increases rapidly after 13 weeks, reaching a peak at term. In blood, P is mainly associated with corticosteroid-binding protein (CBG) and albumin. Most of the P in the blood is bound and very few are free. Progesterone is mainly degraded in the liver and reduced to progesterone, which is then excreted through the kidney after being combined with sulfuric acid or glucuronic acid. P has important physiological effects on regulating the menstrual cycle and maintaining pregnancy. It can promote the transformation of the endometrial secretion phase and prepare for implantation of fertilized eggs; relax the uterine muscles and reduce the reactivity to prostaglandins and oxytocins; inhibit tubal rhythm Sexual contraction. P also promotes breast acinar hyperplasia, increases energy metabolism, raises basal body temperature, and promotes the elimination of water and sodium. P has positive and negative feedback effects on the hypothalamic-pituitary system, and can regulate the synthesis and secretion of pituitary gonadotropins. A small amount of progesterone and E3 before ovulation induced a peak of LH before ovulation, and a large dose of P after ovulation showed negative feedback on the hypothalamus-pituitary system.