Changing Basal and Stimulated Activity of the Renin‐angiotensin System During the Second Half of Gestation in the Anaesthetized Piglet

Abstract

SUMMARYConcentrations 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-'.h-I (mean +S.E.M.) at 57 d to 17 5 + 2 7 ng. ml-'. h-1 at 93 d of gestation and thereafter declined to 5 0 + 1 6 ng. ml-'. 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 lug.ml-1) was not different from that at 57d (050+0 18/ug.ml-1) or that at 93d (031±+008/,ag.ml-1) of gestation. Plasma angiotensin II concentrations increased from 33 (log10 (mean + S.E.M.) = 1-554 + 0 050) pg. ml-' at 60 d to 232 (2 365 + 0 225) pg. ml-' 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.