Progesterone is a steroid hormone involved in reproductive regulation, menstrual cycle coordination, pregnancy maintenance, nervous system signaling, immune modulation, and preparation of reproductive tissues for implantation. The hormone plays a central role during the luteal phase of the menstrual cycle by preparing the uterine lining for potential embryo implantation and supporting early pregnancy physiology. Progesterone also influences cervical mucus composition, uterine contractility, breast tissue development, and thermoregulatory signaling.
Beyond reproductive tissues, progesterone affects nervous system function, sleep-related signaling, vascular tone, immune adaptation, and fluid balance. The hormone interacts with neurotransmitter systems including GABA-related pathways and can influence neural excitability and mood-related physiology. Progesterone also contributes to maintenance of pregnancy by reducing excessive uterine contractions and supporting immune tolerance within the maternal-fetal environment.
Progesterone is produced mainly by the corpus luteum after ovulation and by the placenta during pregnancy. Smaller amounts are synthesized by adrenal glands and nervous tissue. The hormone is synthesized from cholesterol through pregnenolone intermediates using steroidogenic enzymes within luteal and placental cells.
During early pregnancy, human chorionic gonadotropin supports corpus luteum progesterone production until placental steroidogenesis becomes sufficient. Progesterone circulates largely bound to albumin and corticosteroid-binding globulin, while a smaller free fraction enters target tissues and activates intracellular progesterone receptors.
Progesterone production is regulated by the hypothalamic-pituitary-gonadal axis, luteinizing hormone signaling, placental endocrine activity, and reproductive-cycle timing. Following ovulation, luteinized granulosa cells increase progesterone synthesis under LH stimulation. If implantation occurs, hCG maintains luteal progesterone production until placental transfer occurs.
Progesterone acts mainly through progesterone receptors A and B, regulating transcription of genes involved in reproductive tissue differentiation, immune adaptation, vascular signaling, and uterine stability. Nutritional status, stress hormones, inflammatory pathways, aging, and reproductive stage can influence progesterone production and receptor responsiveness. Through these integrated endocrine systems, progesterone coordinates reproductive timing, pregnancy physiology, neural signaling, and maternal tissue adaptation.
Progesterone is the principal progestogen coordinating luteal-phase and gestational endometrial programs, acting via PR with both genomic and rapid effects.
