Effect of prolonged catecholamine infusion on heart rate, blood pressure, breathing, and growth in fetal sheep

Abstract

Norepinephrine and epinephrine were infused into fetal sheep for 24 h to compare the effects on fetal heart rate, blood pressure, breathing movements, and tissue growth with those of prolonged reductions in uterine blood flow. Norepinephrine concentrations increased (p < 0.01) from 871 ± 71 to 6831 ± 1090 pg/mL (2 h) with norepinephrine infusion, and epinephrine concentrations increased from 310 ± 95 to 1424 ± 288 pg/mL (2 h) with epinephrine infusion. Fetal pH decreased (p < 0.01) from 7.37 ± 0.01 to 7.29 ± 0.02 at 0.5 h of the norepinephrine infusion and returned to control values by 2 h, whereas fetal lactate concentrations increased (p < 0.05) from 1.6 ± 0.2 to 4.6 ± 1.0 mmol/L at 2 h and remained elevated for 12 h. Lactate concentrations also increased with epinephrine infusion. Fetal heart rate increased (p < 0.05) from 176 ± 5 to 246 ± 6 and 220 ± 6 beats/min in the 1st h of norepinephrine and epinephrine infusions, respectively, with a subsequent decline. Fetal blood pressure increased (p < 0.05) from 43 ± 3 and 40 ± 2 to 53 ± 3 and 47 ± 2 mmHg (1 mmHg = 133.3 Pa) during the 1st h of norepinephrine and epinephrine infusions, respectively, remaining elevated for 24 h. Fetal body weights were not different between the groups of animals, although liver/body weight ratio was less (p < 0.05) in epinephrine-infused fetuses (0.030 ± 0.001) compared with vehicle-infused animals (0.036 ± 0.002). There was no change in DNA synthesis rate in any of the fetal organs, despite changes in organ-specific DNA and protein content. Our results indicate that the changes in fetal cardiovascular and behavioural function, as well as tissue growth, that occur with prolonged reductions in uterine blood flow are not mediated solely by elevated circulating catecholamine concentrations.Key words: fetal physiology, catecholamines, pregnancy.