Roles Of Progesterone And Estrogens In Sustaining Pregnancy

As its name implies, progesterone is essential for maintaining all stages of pregnancy, and pharmacologic blockade of its actions at any time terminates the pregnancy. Progesterone sustains pregnancy by opposing the forces that conspire to increase uterine contractility and expel the fetus. One of these forces is physical stretch of the myometrium by the growing fetus. Stretch or

progesterone

FIGURE 8 Effects of estrogen on production of placental steroid hormones. By increasing uterine blood flow and inducing low-density lipoprotein (LDL) and the P450 side-chain cleavage (P450scc) enzyme, estrogens increase placental production of pregnenolone, which is used as substrate for androgen production in the fetal adrenals. Uptake of LDL from the maternal circulation may also transfer cholesterol to the fetal circulation. DHEA-S, dehydroepiandrosterone sulfate; 16a-DHEA-S, 16a hydroxy-dehydroepiandrosterone sulfate; CRH, corticotropin releasing hormone; ACTH, adrenocorticotropic hormone; hCG, human chorionic gonadotropin.

progesterone

FIGURE 8 Effects of estrogen on production of placental steroid hormones. By increasing uterine blood flow and inducing low-density lipoprotein (LDL) and the P450 side-chain cleavage (P450scc) enzyme, estrogens increase placental production of pregnenolone, which is used as substrate for androgen production in the fetal adrenals. Uptake of LDL from the maternal circulation may also transfer cholesterol to the fetal circulation. DHEA-S, dehydroepiandrosterone sulfate; 16a-DHEA-S, 16a hydroxy-dehydroepiandrosterone sulfate; CRH, corticotropin releasing hormone; ACTH, adrenocorticotropic hormone; hCG, human chorionic gonadotropin.

tension coupled with estrogens and progesterone promotes myometrial growth and hypertrophy in parallel with growth of the conceptus. Estrogens promote expression of genes that code for contractile proteins, gap junction proteins that electrically couple myometrial cells, oxyto-cin receptors, receptors for prostaglandins, ion channel proteins, and doubtlessly many others that directly or indirectly tend to increase contractility. Throughout pregnancy, estrogens act through a positive feedback mechanism not only to increase their own production but also to increase synthesis of progesterone, which suppresses their excitatory effects (Fig. 8). Estrogens accelerate progesterone synthesis by increasing the delivery of its precursor substrate, cholesterol, to the trophoblast and by upregulating P450scc. Estrogens increase uterine blood flow by stimulating endothelial cells to produce the potent vasodilator nitric oxide and promote uterine formation of prostaglandin I, which is also a vasodilator. In addition, they increase receptor-mediated cholesterol uptake by stimulating expression of LDL receptors. Pregnenolone and LDLs that cross the placenta and enter the fetal circulation serve as substrates for adrenal production of DHEA-S. DHEA-S is then converted by the placenta to estrogens in what amounts to a positive feedback system that progressively increases estrogen production in parallel with progesterone production.

Psychology Of Weight Loss And Management

Psychology Of Weight Loss And Management

Get All The Support And Guidance You Need To Be A Success At The Psychology Of Weight Loss And Management. This Book Is One Of The Most Valuable Resources In The World When It Comes To Exploring How Your Brain Plays A Role In Weight Loss And Management.

Get My Free Ebook


Post a comment