The intrauterine to intra-arterial pressure ratio: a new parameter for the study of uterine contractility physiology.

The objective of the study was to examine the uterine contractions and the arterial perfusion pressure changes after application of oxytocin, endothelin 1, prostaglandins PGE(1), PGE(2) and PGF(2alpha), in order to identify the substance with the greatest intrauterine pressure (IUP)/intra-arterial pressure (IAP) ratio, which means the substance most suitable for inducing uterine contractility without raising the systemic vascular pressure. Increasing doses of oxytocin, endothelin 1, PGE(1), PGE(2) and PGF(2alpha) were applied as bolus injection through the uterine artery of perfused swine uteri and the intrauterine and intra-arterial pressure rises were recorded. All substances showed a significant cervicofundic pressure gradient and, with the exception of PGF(2alpha), the uterine peristalsis moved towards the cervix uteri. The perfusion pressure after application of oxytocin, PGE(1), PGE(2) and PGF(2alpha) reached a maximum value and started to decrease, whereas endothelin 1 caused a continuous increase in the perfusion pressure. Endothelin 1 showed the lowest IUP/IAP ratio and oxytocin the greatest. In conclusion, the IUP/IAP ratio provides a promising new parameter for the study of uterine contractility physiology. Besides oxytocin, PGE(2) and PGF(2alpha) emerged as the best candidate substances to improve uterine contractility without raising the intra-arterial pressure.