The influence of mode of delivery, obstetric analgesia and anaesthesia on the response of isolated human chorionic plate arteries to angiotensin II.

A six point concentration: response curved of the contractile effect of angiotensin II (AII) on helically-cut strips of human chorionic plate artery strips were established at final concentrations of between 10(-14) to 10(-9) M. The tissues were obtained from the placentae of primigravid patients who had normal pregnancy, and also from those with pregnancy induced hypertension (PIH). The tissue response were then related to mode of delivery, obstetric analgesia, and anaesthesia. A total of 36 chorionic plate arteries from 12 primigravid patients were studied. i) The overall initial EC50s of the tissues ranged from 8.0 x 10(-13) M and 4.5 x 10(-13) M. The tissues from PIH patients were significantly more sensitive to AII, when compared with tissues from the normotensive subjects (P greater than or equal to 0.01 less than or equal to 0.05). ii) The tissues from epidural vaginal deliveries were also significantly more sensitive to AII, than those from both normal vaginal deliveries and caesarean deliveries respectively. The median gradients of the semi-log transformed concentration response curved were 2.4 +/- 0.18; 1.27 +/- 0.37, and 1.5 +/- 0.49, for epidural, Caeserean and normal vaginal deliveries respectively. iii) It is suggested that whilst Lumbar epidural analgesia may be of great value in pain relief in labour and in the control of intrapartum hypertension in pre-eclampsia, this procedure may be associated with hypersensitivity and perhaps vasospasm of the placental vasculature to vasoactive agents invivo.