The cardiovascular effects of oxytocic drugs.

The effects of ergometrine 0.5 mg i.v. and of synthetic oxytocin 5 units i.v. on the alpha and the beta adrenoceptive blood vessels of the foreann have been studied by means of volume-pulse plethysmography in 40 gynaecological patients. Ergometrine constricted the alpha and the beta blood vessels. It is thought that the widespread vasoconstriction may precipitate post-partum hypertension or pulmonary oedema in obstetric patients when other alpha vasoconstrictive factors are present. Synthetic oxytocin caused transient dilatation of the alpha and the beta adrenoceptive blood vessels and predisposed to severe postural hypotension. The hypotensive effect of the oxytocin was much less when the drug was given to patients who were in the lithotomy position. It was concluded that oxytocin is preferable to ergometrine in obstetric patients in whom an alpha vasoconstrictive tendency has been induced by one or other of the several factors described.