Effects of urea on the in vitro production of prostaglandins and on urinary excretion in Brattleboro rats.

Brattleboro rats with hereditary diabetes insipidus make it possible to investigate effects of the urea concentration on the in vitro and in vivo production of prostaglandins E2 and F2 alpha (PGE2 and PGF2 alpha) by the renal papilla independently of any vasopressin effects. The rates of prostaglandin production in vitro are increasing between 100 and 1030 mmol/l urea and decreasing above 1030 mmol/l. The ratio PGE2/PGF2 alpha remains constant at about 4. Normally hydrated and 24 h water-deprived animals in steady state of urine formation were compared in vivo. Urine osmolality increased from 167 +/- 6 (N = 5) to 1113 +/- 35 (N = 15) mosmol/kg water and papillary urea concentration from 50 +/- 7 to 304 +/- 19 mmol/l after water deprivation. Urinary excretion rates of PGF2 alpha increased from 0.83 +/- 0.12 to 3.80 +/- 0.37 ng/h. The excretion of PGE2 was unaffected. PGE2 + PGF2 alpha excretion rates increased from 1.62 +/- 0.25 to 4.61 +/- 0.42 ng/h. These values are in accordance with values predicted from work with Sprague-Dawley rats. Together with previously published data on Sprague-Dawley rats these results indicate that variations of prostaglandin production in the conscious rat in steady state of urine formation can be accounted for by variations of plasma vasopressin and of papillary urea concentration. Variations in the excretion fraction are due to other causes.