Oxytocin Acetate 5mg

The action begins by binding to the specific α-hypophamine receptor (OXTR) on the membrane of womb non-striated pulp cells. OXTR belongs to the G protein coupled receptor (GPCR) family and has seven transmembrane domains. It is a peptide hormone composed of 9 amino acids, and the 8th amino acid (leucine) and 3rd amino acid (isoleucine) in its molecular structure are key sites for recognizing and binding to the α-hypophamine receptor. The binding of α-hypophamine acetate to OXTR is highly specific, like a precise match between a key and a lock.

During pregnancy, the expression level of OXTR on womb non-striated pulp cells significantly increases with gestational age, especially reaching its peak during labor. This greatly enhances the sensitivity of the uterus to the substance, providing a physiological basis for the drug to exert its effects on induction and labor. For example, in early pregnancy, due to low expression of OXTR, the uterus is insensitive to α-hypophamine; In late pregnancy, even lower doses of α-hypophamine can cause significant womb contractions.

When it binds to OXTR, it activates the coupled G protein (G α q/11), triggering a series of intracellular signaling events:
Phospholipase C activation: The activated G protein further activates phospholipase C - β (PLC - β), promoting the hydrolysis of phosphoinositol diphosphate (PIP2) on the cell membrane to oxytocin acetate inositol triphosphate (IP3) and diacylglycerol (DAG).
Calcium ion release: IP3 binds to specific receptors on the sarcoplasmic reticulum (SR), prompting SR to release stored calcium ions (Ca2+) into the cytoplasm, resulting in a rapid increase in intracellular Ca2+concentration. The intracellular Ca2+concentration can increase from a resting state of 10 ⁻⁷ M to 10 ⁻⁵ M.

Activation of protein kinase C: DAG remains on the cell membrane, activating protein kinase C (PKC). The activation of PKC further activates the mitogen activated protein kinase (MAPK) cascade, leading to the activation of phospholipase A2 (PLA2) and the production of prostaglandin E2 (PGE2). PGE2 not only directly promotes womb non-striated pulp contraction, but also regulates local physiological activity of the womb pulp layer through paracrine signaling, enhancing the effect of womb contraction.

The increase in intracellular Ca2+concentration is the direct cause of uwomb non-striated pulp contraction. The specific process is as follows:
Calcium calmodulin complex formation: Ca2+binds to calmodulin (CaM) to form Ca2+- CaM complex.
Myosin light chain kinase activation: Ca2+- CaM complex activates myosin light chain kinase (MLCK).
Myosin phosphorylation: MLCK catalyzes the phosphorylation of myosin light chain (MLC).
Actin myosin interaction: Phosphorylated MLC interacts with actin to form a transverse bridge loop, generating contractility and causing womb non-striated pulp to contract.

The womb contractions it causes are dose-dependent:
Low dose: mainly triggers rhythmic contractions of the uterus, with a contraction frequency of about 2-4 times/10 minutes, and each contraction lasts for 30-60 seconds. This contraction pattern is similar to physiological contractions, which helps to promote the progress of labor and facilitate the smooth delivery of the fetus.
High dose: can induce rigid contractions of the uterus, keeping the womb pulp layer in a continuous state of contraction. This contraction can quickly compress the blood vessels in the womb pulp layer, effectively close the blood sinuses on the placental detachment surface, reduce postpartum bleeding, and play a key role in the prevention and treatment of postpartum bleeding.

High concentrations of α-hypophamine acetate can also promote cervical maturation by promoting the activity of prostaglandin synthase in cervical tissue, accelerating the degradation of collagen fibers and matrix remodeling
Increased synthesis of prostaglandins: The enhanced activity of prostaglandin synthase leads to an increase in prostaglandin synthesis. Prostaglandins can regulate the metabolism of cervical extracellular matrix, promote the activity of collagenase, and break down collagen fibers in the cervix.

Cervical softening and dilation: At the same time, prostaglandins can increase the moisture and elastin content of the cervix, thereby softening and dilating it. This process creates favorable conditions for vaginal delivery, allowing the fetus to pass through the cervix more smoothly. For example, during the induction of labor process, it can not only directly act on the non-striated pulp of the uterus to induce womb contractions, but also promote cervical maturation, shorten the labor process, and improve the success rate of vaginal delivery.

It also has a contractile effect on the myoepithelial cells surrounding the mammary gland acini. The lobular branches of the breast are surrounded by contractile myoepithelial cells, which are highly sensitive to α-hypophamine acetate. When it acts on myoepithelial cells, it causes them to contract, resulting in smooth and rhythmic contractions of the ducts and sarcomeres. This contraction effect helps milk flow from the acini into the milk ducts, completing the process of milk ejection reflex and promoting milk excretion. During lactation, appropriate application can promote milk secretion, but in clinical practice, it is generally used more for its physiological lactation promoting effect rather than deliberate lactation. But in some cases where milk stasis is caused by blocked breast ducts, reasonable use may help improve milk excretion.

Cardiovascular effects: Low doses of oxytocin acetate may dilate peripheral blood vessels and cause reflex tachycardia. This is because it acts on receptors on vascular non-striated pulp cells, activating signaling pathways within the cells, leading to vasodilation. However, when used in large doses or for a long time, it may activate the OXTR on the renal tubules, produce antidiuretic effect, cause water and sodium retention, and increase the risk of "water poisoning".
Neuromodulatory effect: It can also act on neurons in the paraventricular nucleus and supraoptic nucleus of the hypothalamus, affecting social behavior and maternal infant attachment through the limbic system. In animal experiments, it has been shown to enhance maternal nurturing behavior and promote emotional connections between mother and baby.