Chemistry, Secretion, Functions and Regulations of Gonadal hormones: Progesterone

 

1. Chemistry

  • Progesterone is a C-21 steroid hormone, belonging to the progestogen group.

  • Chemical formula: C₂₁H₃₀O₂.

  • Derived from cholesterol via the steroidogenesis pathway.

  • It is a lipid-soluble hormone and acts via intracellular nuclear receptors (Progesterone Receptors: PR-A and PR-B).


2. Secretion

  • • Progesterone is synthesized in the ovaries mainly from cholesterol.

    • Normal secretions level 

    • Female pre ovulation/male/post-menopausal=1ng/ml

    • Female mid cycle=5-20ng/ml

    • Pregnancy 

    1st trimester=11 to 90ng/ml

    2nd trimester=25 to 89ng/ml

    3rd trimester=48 to 150/300ng/ml.

  • In Females

    • Secreted mainly by the corpus luteum after ovulation.

    • Also produced by the placenta during pregnancy (from ~8–12 weeks onward).

    • Minor secretion by adrenal cortex.

  • In Males

    • Secreted in small amounts by testes (Leydig cells) and adrenal cortex.

3. Functions

  • Reproductive Functions

    • Prepares the endometrium for implantation (secretory phase changes).

    • Maintains pregnancy by suppressing uterine contractions.

    • Supports development of placenta.

  • During Pregnancy

    • Maintains uterine quiescence (inhibits oxytocin receptor expression).

    • Stimulates mammary gland alveolar development (with estrogen).

  • Other Functions

    • Modulates immune tolerance during pregnancy.

    • Influences brain function (neurosteroid role).

    • Increases basal body temperature after ovulation.

4. Regulation


  • Hypothalamic-Pituitary-Gonadal Axis

    • GnRH (hypothalamus) → stimulates release of LH (pituitary).

    • LH surge at mid-cycle → ovulation → corpus luteum formation → progesterone secretion.

  • Feedback Mechanism

    • Progesterone exerts negative feedback on GnRH and LH/FSH secretion.


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