Potassium: aldosterone relationships in pregnant ewes and chronically cannulated ovine fetuses

As maternal hyperkalemia quickly induces fetal hyperkalemia, it was decided to investigate the effect of small elevations of plasma [K+] on the peripheral blood aldosterone concentration in chronically catheterized ovine fetuses and to compare this response to that obtained in the adult ewe both pregnant and nonpregnant. Fol elevations of plasma [K+] of 0.1 to 0.3 mmole/liter blood aldosterone concentrations were elevated by 6.7 +/- 4.9 (9) ng/dl in nonpregnant sheep, 6.3 +/- 5.0 (6) in pregnant ewes, but only 0.3 +/- 1.7 (4) in fetal sheep. For increments in plasma [K+] of 0.4--1.0 mmole/liter aldosterone increments in nonpregnant ewes were 9.5 +/- 4.5 (4) ng/dl compared with 10.1 +/- 4.7 (5) in pregnant ewes and 1.5 +/- 2.6 (7) in fetuses. There was no obvious correlation between the age of the fetus and the response to increased plasma [K+]. In effect, the blood aldosterone concentration of the fetus was not elevated by increasing plasma plasma [K+].

The ovine fetus is not able to cope with hyperkalemia by increasing blood aldosterone concentration. Until the fetus is close to term, hyperkalemia may jeopardize the pregnancy by causing placental hemorrhages.