1. Platelet angiotensin II binding, circulating angiotensin II levels, plasma renin substrate and plasma renin concentration were measured in a longitudinal study of 30 women during pregnancy and the puerperium.
2. There was a significant fall in platelet angiotensin II binding from 11 weeks gestation to 18 weeks gestation (P < 0.01). There were no further significant changes in platelet angiotensin II binding until after delivery, a significant rise in platelet angiotensin II binding being found at 6 weeks post partum as compared with at 36 weeks gestation (P < 0.01). There was no further significant change from 6 to 12 weeks post partum, and platelet angiotensin II binding at 6 and 12 weeks post partum in the pregnant cohort approximated to that in non-pregnant women. These changes parallel those known to occur in pressor responsiveness to angiotensin II in pregnancy.
3. Plasma angiotensin II concentration, plasma renin substrate and plasma renin concentration were all significantly higher during pregnancy than in the puerperium (P < 0.001). There were no significant changes during pregnancy in plasma angiotensin II concentration or plasma renin concentration, although plasma renin substrate rose throughout.
4. Significant inverse correlations between platelet angiotensin II binding and plasma angiotensin II concentration (P < 0.01), plasma renin substrate (P < 0.01) and plasma renin concentration (P 0>001) were found during pregnancy. These data suggest that down-regulation of platelet angiotensin II binding by the components of the renin-angiotensin system pertains in pregnancy.
5. We are currently investigating parallelism between platelet and vascular angiotensin-binding sites. If such is confirmed, studies of platelet angiotensin II binding in pregnancy may be of both basic physiological and clinical interest in relation to the hypertensive diseases of pregnancy.