RENAL NERVE EFFECTS ON RENAL ADAPTATION TO CHANGES IN SODIUM-INTAKE DURING OVINE PREGNANCY

To assess the possibility of an enhanced role of renal nerves in the control of urinary sodium excretion (U(Na)V) and fluid homeostasis during pregnancy, urine output, U(Na)V, and urinary potassium excretion were assessed hourly for 3 days before and for 6 days after a step reduction in total daily sodium intake from 400 to 40 mmol. Studies were performed in normal conscious sheep (4 nonpregnant and 4 pregnant). Each animal was prepared with a divided bladder so that urine could be collected simultaneously from one normally innervated and one denervated kidney. In nonpregnant ewes, ratios of the rates of excretion by denervated vs. innervated kidneys for U(Na)V averaged 1.00 +/- 0.07 under steady-state conditions at high levels of sodium intake. This ratio was not different at the low-sodium-intake state. In contrast, this ratio was 1.15 +/- 0.07 at high sodium intake and 1.13 +/- 0.03 at low sodium intake in pregnant ewes. The ratios at both steady-state levels were different (P < 0.05) between nonpregnant and pregnant sheep. During the transition between sodium intake states, these ratios were unchanged in nonpregnant animals, whereas pregnant animals exhibited peak ratios of 2.20 +/- 0.39 (P < 0.05), indicating sodium wasting by the denervated kidneys. In summary, the data suggest that renal nerve activity may not be completely suppressed by high sodium intakes in pregnant sheep. Furthermore, the renal nerves have an enhanced influence on sodium conservation during and after the transition from high- to low-sodium-intake states during pregnancy. Consequently, the studies suggest that renal nerves contribute to the control of fluid and electrolyte homeostasis and to the maintenance of a positive sodium balance in the pregnant ewe.