The contractile activity and tone of myometrium are regulated by neurohumoral mechanisms. Myometrium contains M-cholinoceptors as well as α- and β2-adrenoceptors. Activation of M-cholinoceptors and α-adrenoceptors stimulates the myometrium, whereas stimulation of β2-adrenoceptors suppresses it. Moreover, contractile activity of the myometrium is significantly affected by female sex hormones, such as estrogens, oxytocin (which is a hormone of the posterior lobe of the pituitary) and prostaglandins. Also, some endogenous substances suppress the contractile activity of the myometrium (such as progesterone and, perhaps, prostacyclin). Pharmacological regulation of contractile myometrial function can be achieved by using these endogenous substances or medications that alter neurogenic or humoral effects on the uterus.
The agents affecting the contractility and tone of the uterus are subdivided into the following groups.
I • Drugs predominantly affecting the contractile activity of myometrium
= Agents increasing the contractile activity of the myometrium (myometrial stimulants)
□ Hormones and drugs of the posterior lobe of the pituitary
- Oxytocin
- Pituitrinum
□ Prostaglandin drugs
- Dinoprost (prostaglandin F2α)
- Dinoprostone (prostaglandin E2)
= Agents decreasing the contractile activity of the myometrium (tocolytic drugs; myometrial relaxants)
□ Predominantly stimulating β2-adrenoceptors
- Fenoterol
- Salbutamol
□ Drugs used for general anesthesia
- Sodium hydroxybutyrate
□ Other agents
- Magnesium sulphate
II • Drugs predominantly increasing the tone of the myometrium
= Agents of plant origin (alkaloids and ergot preparations)
- Ergometrine
- Ergotamine
- Ergot extract
- Ergotalum
= Synthetic drugs