Progesterone

Progesterone is produced in the ovaries (specifically after ovulation in the corpus luteum), the adrenal glands (near the kidney), and, during pregnancy, in the placenta. Progesterone is also stored in adipose (fat) tissue. An additional source of progesterone is 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.

Reproductive system

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 it 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.[25]
• 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 steroids.

Nervous system

Progesterone, like pregnenolone and dehydroepiandrosterone, belongs to the group of neurosteroids. It can be synthesized within the central nervous system and also serves as a precursor to another major neurosteroid, allopregnanolone.

Neurosteroids affect synaptic functioning, are neuroprotective, and affect myelination. They are investigated for their potential to improve memory and cognitive ability. Progesterone affects regulation of apoptotic genes.

Its effect as a neurosteroid works predominantly through the GSK-3 beta pathway, as an inhibitor. (Other GSK-3 beta inhibitors include bipolar mood stabilizers, lithium and valproic acid.)

Other systems

• It raises epidermal growth factor-1 levels, a factor often used to induce proliferation, and used to sustain cultures, of stem cells.
• It increases core temperature (thermogenic function) during ovulation.[27]
• It reduces spasm and relaxes smooth muscle. Bronchi are widened and mucus regulated. (Progesterone receptors are widely present in submucosal tissue.)
• It acts as an antiinflammatory agent and regulates the immune response.
• It reduces gall-bladder activity.[28]
• It normalizes blood clotting and vascular tone, zinc and copper levels, cell oxygen levels, and use of fat stores for energy.
• It may affect gum health, increasing risk of gingivitis (gum inflammation) and tooth decay.
• It appears to prevent endometrial cancer (involving the uterine lining) by regulating the effects of estrogen.

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