ABSTRACT
Aldosterone, corticosterone, cortisol, 11-deoxycortisol and 11-deoxycorticosterone were measured, using a double isotope dilution derivative assay, in whole blood samples of ovine foetuses bearing chronic vascular cannulae. All values are quoted as mean ± standard error of mean. n = number of samples. Parturition occurred at 142–152 days. The concentration of aldosterone (ng/100 ml blood) was 8.7 ± 2.5 at 100–109 days, (n = 8), 4.4 ± 1.2 at 110–140 days (n = 32) and 11.5 ± 2.0 (n = 6) at 140 days until term. The value in unstressed, sodium replete pregnant sheep was 1.2±0.4 (n = 12). Neither corticosterone nor 11-deoxycortisol concentrations varied throughout gestation and were respectively 0.08 ± 0.02 and 0.03 ± 0.04 μg/100 ml blood in 56 samples. These values are essentially the same as those of pregnant, unstressed sheep. Total blood cortisol concentration was 0.10 ± 0.01 μg/100 ml in 38 samples from foetuses younger than 135 days, which is lower than the value for pregnant, unstressed sheep of 0.43 ± 0.07 (n = 34). Cortisol values rose after 135 days to reach 0.93 ± 0.3 (n = 7) after 140 days. The concentration of 11-deoxycorticosterone was 33.8 ± 8.0 ng/100 ml blood (n = 7) in the period 100–109 days, then decreased to 18.7 ± 4.4 (n = 45) from 110 days to term. The concentration in unstressed pregnant sheep was 26.3 ± 10 (n = 10) which is higher than non-pregnant sheep 2.33 ± 0.65 (n = 30). Infusions of ACTH (Synacthen®) 5 IU/h for 90 min had no consistent effect on the peripheral blood concentration of aldosterone, 11-deoxycorticosterone or 11-deoxycortisol at any stage, but elevated corticosterone values significantly (P < 0.01) in all foetuses. Cortisol concentrations were significantly elevated (P < 0.05) in foetuses of 135 days gestation or older.
Optimization of the double isotope dilution
