1. The influence of urine pH on the urinary excretion of prostaglandin (PG) F2α and the PGE2/PGF2α ratio has been examined in the conscious rat.
2. The basal urinary PGF2α excretion rate of 3.9 pmol/h (n = 23) did not vary with urine pH. In marked contrast, PGE2 excretion increased as the urine became more alkaline. The PGE2/PGF2α ratio therefore progressively increased from 1.5 to 22 as the pH of the urine changed from pH 5.8 to pH 7.8.
3. The independence of PGF2α excretion from urine pH: (a) excludes cyclo-oxygenase as a potential site of action for the pH-dependence of urinary PGE2 excretion; (b) suggests that the urinary PGE2/PGF2α ratio measured in alkaline urine may be a more accurate reflection of the kidneys, ability to synthesize these two prostaglandins in vivo; (c) suggests that control of urine pH is required before the urinary PGE2/PGF2α ratio can be employed as an index of PGE2 9-ketoreductase (EC 126.96.36.199) activity in vivo.