The effect of inhibition of prostaglandin synthesis on tubuloglomerular feedback in the rat kidney

To further clarify the mechanism mediating the reduction of nephron filtration rate in response to an increase of loop of Henle flow rate we have studied the effect of prostaglandin inhibition on tubuloglomerular feedback in rats. Following inravenous administration of 2 or 5 mg/kg indomethacin feedback responses expressed as the percent reduction of early proximal flow rate (EPFR) during flow elevation from 0–40 nl/min decreased from control values of –54.3±4.3% (mean ± S.E.) and –39.5±3.9% to –27.9±2.8% (P<0.001) and –5.0±4.9% (P<0.001) respectively. A significant reduction in the feedback response was also seen following intravenous administration of 2 or 5 mg/kg Ro 20-5720 (–28.8±5.8% and –7.8±3.8% respectively), 10 mg/kg meclofenamate (–15±4%), and 2 mg/kg eicosa-5,8,11,14-tetraynoic acid (–16.2±4.8%). In contrast to control animals injection of 5 mg/kg indomethacin had no effect on the feedback response in rats kept on a low salt diet. After applying a single dose of 5 mg/kg indomethacin or Ro 20-5720 feedback responses were reduced to –5.4±4.3% and –3.0±4.36% in the period 0–80 min, but were normal in the period 81–160 min after injection (–36.1±2.83% and –44.3±2.82% respectively). A dose dependent inhibition of the feedback response was also noted when indomethacin was applied intraluminally with full inhibition being established at a concentration of 0.5 mM. Urinary excretion rates of PGE₂ and PGF₂ fell from control values of 286.1±73.7 and 143.5±25.9 pg/min to 31.2±9.9 and 23.6±9 pg/min following 2 mg/kg indomethacin and to 36.8±4.4 and 8.9±1.9 pg/min following 5 mg/kg Ro 20-5720. Reduction of PG excretion was not reversible during the time of the experiment. Our results demonstrate a consistent decrease of tubuloglomerular feedback responses during inhibition of prostaglandin biosynthesis.Supported by the Deutsche Forschungsgemeinschaft