1. The effects of chronic alterations in dietary sodium intake on urinary prostaglandin (PG) E2 and thromboxane (TX) B2 was investigated in the rabbit.
2. Sodium restriction, over a 15-day period, reduced daily urinary PGE2 and TXB2 in concordance with urinary flow (V) and sodium excretion (UNa+V), but increased plasma renin activity (PRA) and plasma aldosterone concentration (PAC).
3. Sodium repletion, on the other hand, increased urinary PGE2 and TXB2 in proportion to the rise in V, but reduced PRA and PAC.
4. During both sodium diets PGE2 and TXB2 correlated positively with V and negatively with PRA.
5. It is concluded that chronic sodium intake produces opposite changes in the renal prostaglandin and the renin–angiotensin systems.