Progesterone is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy (supports gestation) and embryogenesis of humans and other species. Progesterone belongs to a class of hormones called progestogens, and is the major naturally occurring human progestogen.
Progesterone should not be confused with progestins, which are synthetically produced progestogens.
Progesterone was independently discovered by four research groups.
Willard Myron Allen who co-discovered Progesterone with his anatomy professor George Washington Corner at the University of Rochester Medical School in 1933. Allen first determined its melting point, molecular weight, and partial molecular structure. He also gave it the name Progesterone derived from Progestational Steroidal ketone.
Like other steroids, progesterone consists of four interconnected cyclic hydrocarbons. Progesterone contains ketone and oxygenated functional groups, as well as two methyl branches. Like all steroid hormones, it is hydrophobic.
Progesterone is produced in the adrenal glands, the gonads (specifically after ovulation in the corpus luteum), the brain, and, during pregnancy, in the placenta.
In humans, increasing amounts of progesterone are produced during pregnancy:
Initially, the source is the corpus luteum that has been “rescued” by the presence of human chorionic gonadotropins (hCG) from the conceptus.
However, after the 8th week production of progesterone shifts over to the placenta. The placenta utilizes maternal cholesterol as the initial substrate, and most of the produced progesterone enters the maternal circulation, but some is picked up by the fetal circulation and is used as substrate for fetal corticosteroids. At term the placenta produces about 250 mg progesterone per day.
Juts to let you know After radiation there may also be done for progesterone (another hormone) receptors. The benefits of hormone therapy are less clear for people whose breast cancer is only progesterone receptor positive (PR+ and ER-). Very few breast cancers fall into this category. However, if this is the case for you your specialist will discuss whether hormone therapy is appropriate.
An additional source of progesterone are milk products. They contain much progesterone because on dairy farms cows are milked during pregnancy, when the progesterone content of the milk is high. After consumption of milk products the level of bioavailable progesterone goes up. This observation has resulted in concern that diets high in dairy products might induce pet and human diseases.
Progesterone exerts its action primarily through the intracellular progesterone receptor although a distinct, membrane bound progesterone receptor has also been postulated. Progesterone has a number of physiological effects which are amplified in the presence of estrogen. Estrogen through estrogen receptors upregulates the expression of progesterone receptors.
Progesterone is sometimes called the “hormone of pregnancy”, and it has many roles relating to the development of the fetus:
Progesterone converts the endometrium to its secretory stage to prepare the uterus for implantation. At the same time progesterone affects the vaginal epithelium and cervical mucus, making the mucus thick and impermeable to sperm. If pregnancy does not occur, progesterone levels will decrease, leading, in the human, to menstruation. Normal menstrual bleeding is progesterone withdrawal bleeding.
During implantation and gestation, progesterone appears to decrease the maternal immune response to allow for the acceptance of the pregnancy.
Progesterone decreases contractility of the uterine smooth muscle.
In addition progesterone inhibits lactation during pregnancy. The fall in progesterone levels following delivery is one of the triggers for milk production.
A drop in progesterone levels is possibly one step that facilitates the onset of labor.
The fetus metabolizes placental progesterone in the production of adrenal mineralo- and glucosteroids.
The use of progesterone and its analogues have many medical applications — both to address acute situations, and to address the long-term decline of natural progesterone levels. Because of the poor bioavailability of progesterone when taken orally, many synthetic progestins have been designed. However, the roles of progesterone may not be fulfilled by the synthetic progestins which in some cases were designed solely to mimic progesterone’s uterine effects.