334 POTASSIUM MODULATES FETAL AND NEWBORN ALDOSTERONE SECRETION

The role of serum potassium (K+) in modulation of serum aldosterone concentration (Aldo) during development was studied in chronically-catheterized fetal (134–144 days gestation) and newborn (10–14 days of age) lambs. Dexamethasone phosphate was given to fetuses (0.1 mg/kg/dose) and ewes (5 mg) or newborn lambs (0.1 mg/kg/dose) at 12 hours and 2 hours prior to potassium infusion (KCL) to suppress adrenocorticotropin (ACTH) secretion. Data are expressed as mean ± SD. KCl (1.2±0.4 mEq/kg) in fetuses increased K+ from 4.0±0.5 to 5.4±0.6 mEq/L (p 0.05). Maternal K+ and Aldo also did not change significantly. Similar KCl infusion (1.8±0.1 mEq/kg) in newborns increased K+ in similar fashion (from 3.8±0.1 to 5.5±0.4 mEq/L, p<0.001) but induced a greater increase in Aldo (from 22.6±11.8 to 97.3±46.6 pg/ml, p<0.01). PRA and A-II did not change significantly. If fetuses were given higher dosages of KCl (3.8±0.3 mEq/kg) to increase K+ further (up to 8.2±1.3 mEq/L), Aldo increased proportionately (up to 101±33 pg/ml). Newborns given high dose KCl (4.3±0.3 mEq/kg) increased K+ (to 10.3±2.6 mEq/L) with only slight increment in Aldo (to 125.0±87.8 ng/ml) suggesting near-maximal stimulation. These results suggest that after ACTH suppression, KCl induces increase in Aldo in both fetuses and newborns, but the fetal adrenal is less sensitive to such stimulation.