REDUCED RENAL PERFUSION-PRESSURE CAUSES PROSTAGLANDIN-DEPENDENT EXCITATION OF R2 CHEMORECEPTORS IN RATS

The activity of multiunit preparations of afferent renal nerve activity (ARNA) and single R2 chemoreceptors was recorded during graded reductions in renal perfusion pressure (RPP) produced by tightening an aortic snare in anesthetized rats. In 13 multiunit preparations an initial RPP reduction from 117 +/- 2 to 101 +/- 2 mmHg caused ARNA to increase 29 +/- 5% above control. Further reductions in RPP produced a 65 +/- 11% increase in ARNA at 80 +/- 1 mmHg, 87 +/- 24% at 59 +/- 1 mmHg, and 127 +/- 38% at 37 +/- 1 mmHg (P < 0.01 ARNA vs. RPP). Renal blood flow was measured by pulsed Doppler flowmeter in these rats and showed good autoregulation and minimal reduction (-4 +/- 2%) during the initial pressure drop. Ten single R2 chemoreceptors increased their firing rate by 129 +/- 4% when RPP was reduced from 109 +/- 2 to 85 +/- 2 mmHg and showed a peak response of 494 +/- 105% at 27 +/- 2 mmHg. The activity of 11 R2 receptors increased from 3.7 +/- 1.0 to 6.8 +/- 0.8 impulses/10 s when RPP was reduced from 112 +/- 4 to 79 +/- 2 mmHg. Prostaglandin blockade with indomethacin (6 rats) or meclofenamate (7 rats) caused a decrease in basal activity in the same units to 1.8 +/- 0.5 impulses/10 s and eliminated their excitatory response to a similar reduction in RPP (108 +/- 4 to 75 +/- 3 mmHg). These data support a role for R2 chemoreceptors in neurocirculatory reflexes elicited by reductions in RPP.