Maternal undernutrition at specific stages of pregnancy has been associated with abnormal placental and fetal growth (Heasman et al. 1998). Whilst undernutrition in late gestation has been shown to increase fetal blood pressure (Edwards & McMillen, 2001), the extent to which fetal weight may be related to blood pressure has not been determined in adequately fed ewes.
Seven singleton-bearing Bluefaced Leicester X Swaledale ewes that had been fed to fully meet requirements throughout gestation were entered into this study. At around 110 days gestation, each ewe was given 500 g concentrate and ad libitum hay. Twenty-four hours prior to surgery the ewes were starved and surgery performed at 122 days gestation. Anaesthesia was induced with thiopentone 2.5 % and animals were maintained on oxygen and halothane with mechanical respiration following intravenous infusion of remifentanyl (5 g per 50 ml normal saline) was given intravenously via a syringe driver at a dose of 20-30 ml h-1. A mid-line incision was made to the ewe and a hysterotomy performed to enable access to the fetus. Fetal carotid artery, jugular vein and the amniotic cavity were surgically catheterised to allow measurement of basal blood pressure. At 4 days after surgery, mean, systolic and diastolic blood pressure, were measured for a resting period of 30 min. At 132 days gestation the ewes were humanely killed and lamb and placental weights measured. Results are expressed as means ± S.E.M. and statistically significant relationships were then assessed using a Pearson correlation. All animal procedures were carried out in accordance with current UK legislation.
All fetuses were of normal size (4.0 ± 0.40 kg) with no placental abnormalities (mean placental weight 307 ± 23 g). There was a positive correlation between fetal and placental weights (R 2 = 0.554 (P = 0.055)), between fetal and kidney weights (R 2 = 0.54 (P = 0.06)) and between fetal weight and systolic blood pressure (R 2 = 0.59 (P = 0.05)). A non-significant correlation for placental weight and systolic blood pressure was also observed, but no correlation between fetal PO2 and any of these indices.
In conclusion, in adequately fed ewes at a fixed time in late gestation an increase in total placental and fetal weights together with heavier kidneys is accompanied by a rise in blood pressure. The extent to which such relationships between body and kidney weights and basal blood pressure may extend into later life remains to be established.
S. Pearce was supported by a BBSRC Studentship.