To elucidate the mechanisms responsible for systemic and renal hemodynamic changes in early endotoxemia, the roles of prostaglandins (PG) and renal nerves were investigated. Endotoxin (E, 3 χ/kg i.v.) was given to two groups of anesthetized dogs that had undergone unilateral renal denervation: Group I (n=9) E only; Group II (n=11) E + indomethacin (10 mg/kg i.v.) or meclofenamate (5 mg/kg i.v.). A third group of dogs (Group III, n=5) received indomethacin (10 mg/kg i.v.) only. 1 h after E in group I dogs, mean arterial pressure (MAP) decreased from 126 to 94 mm Hg (P<0.001), and prostacyclin (6-keto-F1α metabolite, PGI2) increased (from 0.64 to 2.08 ng/ml, P<0.005). Glomerular filtration rate (GFR) and renal blood flow (RBF) declined comparably both in innervated and denervated kidneys. In marked contrast, group II dogs had a stable MAP (136-144 mm Hg, NS) and no increase in PGI2 levels. Plasma renin activity (0.7-2.5 ng/ml per h, P<0.005) increased, and renin secretion was greater in innervated compared with denervated kidneys (255 vs. 74 U/min, P<0.01) in these PG-inhibited dogs. In addition, denervated kidneys in group II dogs had a greater GFR (42 vs. 34 ml/min, P<0.01) and RBF (241 vs. 182 ml/min, P<0.01) than innervated kidneys after E. Group III animals had no significant changes in systemic or renal hemodynamics, plasma renin activity or PGI2 during the study. These results suggest that PGI2 mediates the systemic hypotension of early endotoxemia in the PG-intact animal. Moreover, PG inhibition uncovers an important effect of E to increase efferent renal nerve activity with a consequent decline in GFR and RBF independent of changes in MAP. Finally, the results demonstrate that renal nerves are important stimuli to renin secretion in early endotoxemia via pathways that are PG-independent.
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