Which of these is not an important component of initiation of parturition in humans ?

The correct answer is Release of Prolactin.

Parturition (the onset of labor) in humans is triggered by a coordinated hormonal cascade that prepares the uterus and cervix for delivery. The key components include:

1. Release of Oxytocin – Oxytocin is secreted from the posterior pituitary and stimulates strong uterine contractions, which are essential for the expulsion of the fetus.

2. Increase in the estrogen‑to‑progesterone ratio – As pregnancy progresses, estrogen levels rise relative to progesterone. This shift enhances uterine sensitivity to oxytocin and up‑regulates prostaglandin synthesis.

3. Synthesis of Prostaglandins – Prostaglandins (especially PGE₂ and PGF₂α) are produced in the fetal membranes and decidua. They promote cervical ripening and further increase uterine contractility.

These three mechanisms work together to initiate and sustain labor.

In contrast, prolactin is primarily involved in preparing the mammary glands for lactation after delivery. Its release does not play a direct role in the initiation of uterine contractions or cervical changes that define the onset of parturition.

Therefore, among the listed options, Release of Prolactin is the component that is **not** important for the initiation of parturition in humans.