EFFECT OF PROLONGED CATECHOLAMINE INFUSION ON HEART-RATE, BLOOD-PRESSURE, BREATHING, AND GROWTH IN FETAL SHEEP

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 ute rine blood flow. Norepinephrine concentrations increased (p < 0.01) fr om 871 +/- 71 to 6831 +/- 1090 pg/mL (2 h) with norepinephrine infusio n, 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 norepinephrin e infusion and returned to control values by 2 h, whereas fetal lactat e 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 a lso increased with epinephrine infusion. Fetal heart rate increased (p < 0.05) from 176 +/- 5 to 246 +/- 6 and 220 +/- 6 beats/min in the 1s t 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) d uring the 1st h of norepinephrine and epinephrine infusions, respectiv ely, remaining elevated for 24 h. Fetal body weights were not differen t between the groups of animals, although liver/body weight ratio was less (p < 0.05) in epinephrine-infused fetuses (0.030 +/- 0.001) compa red with vehicle-infused animals (0.036 +/- 0.002). There was no chang e 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 n ow are not mediated solely by elevated circulating catecholamine conce ntrations.