CHANGING BASAL AND STIMULATED ACTIVITY OF THE RENIN-ANGIOTENSIN SYSTEM DURING THE SECOND HALF OF GESTATION IN THE ANAESTHETIZED PIGLET

¹ Department of Obstetrics and Gynaecology, Queen's Medical Centre, University of Nottingham, Nottingham
² Institute of Anatomy, Faculty of Veterinary Sciences, State University Utrecht, Yalelaan 1, Utrecht, The Netherlands
³ Department of Anatomy, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Edinburgh EH9 1QH

Concentrations of components of the renin-angiotensin system were studied in eighty anaesthetized pig fetuses aged between 57 and 112 d of gestation (term = 114±1 d). Plasma renin concentration rose from a mean value of 3·2±0·4 ng.ml^-1.h^-1 (mean ± S.E.M.) at 57 d to 17·5±2·7 ng.ml^-1. h^-1 at 93 d of gestation and thereafter declined to 5·0±1·6 ng. ml^-1. h^-1 just prior to term. There was no distinct pattern of change in plasma renin substrate concentrations during gestation; the concentration near term (0·33±0·10 µg.ml^-1) was not different from that at 57 d (0·50±0·18 µg.ml^-1) or that at 93d (0·31±0·08 µg.ml^-1) of gestation. Plasma angiotensin II concentrations increased from 33 (log₁₀ (mean ± S.E.M.) = 1·554±0·050) pg.ml^-1 at 60 d to 232 (2·365±0·225) pg.ml^-1 at 105 d of gestation, after which it decreased to 50 (1·699±0·100) pg.ml^-1 in 20-d-old neonatal piglets. Haemorrhage of 10-20% estimated blood volume produced no consistent changes in plasma renin substrate concentrations, and inconsistent changes in renin and angiotensin II concentrations at 85-90 d of gestation, but a consistent increase in both renin and angiotensin II concentrations thereafter. These results indicate that the components of the renin-angiotensin system are present in the circulation of the pig fetus, and that their responses to stimuli develop during the second half of gestation.