Description: A discussion between Dr. Fiona Broughton Pipkin, University of Nottingham, and Mr. Geoffrey Chamberlain. The following summary accompanies the cassette: Angiotensin II (AII) is an extremely powerful vascoconstrictor hormone, formed by the action of the enzyme renin on an -d-globulin substrate. Levels of renin and AII are high inn normal pregnancy but a specific compensatory diminution in vascular reactivity probably via PGEs, protects against hypertension. In hypertensive pregnancy (PIH), this protection is lost, and levels of AII are usually still further increased. There is a positive statistical relationship between diastolic BP and AII levels in pregnancy in humans and sheep. The administration of an AII receptor blocker to conscious pregnant sheep evokes a dose-dependent fall in blood pressure, the size of which is proportional to initial AII levels. There is also increasing indirect evidence that the feto-placental unit may contribute to circulating ALL levels. It is suggested that the relative ischaemia of the feto-placental unit in PIH results in increased AII production, as in the ischaemic kidney. This then results in increased PGE production in the uterus, which, together with the increased systemic BP improves feto-placental perfusion. This PIH may initially be a physiological response on the part of the feto-placental unit. 6 segments.