Aim: The prostaglandin cyclooxygenase (COX) and P450 cytochrome (CYP450) pathways of arachidonic acid metabolism are functionally interrelated and both engaged in control of sodium excretion; the study focused on their contribution to the natriuresis which follows hypertonic saline infusion in the rat.
Methods: In anaesthetized rats, clearance studies were conducted, supplemented with laser-Doppler measurements of the cortical and medullary blood flow (CBF, MBF), and measurement of medullary tissue admittance (Y), an index of interstitial ion concentration.
Results: Indomethacin (Indo), 5 mg kg(-1) i.v. paradoxically enhanced the natriuresis secondary to intra-aortic suprarenal 5% saline load, further increasing sodium excretion by 385 +/- 73% (P < 0.01). After acute clotrimazole, 10 mg kg(-1) i.v. an inhibitor of CYP450 epoxygenase, the increase in natriuresis was smaller and did not differ from that observed after the drug's ethanol solvent. In rats pre-treated with clotrimazole for 3 days, hypertonic saline loading increased sodium excretion (U(Na)V) to 0.94 +/- 0.22 micromol min(-1) , compared with a significantly greater (P < 0.05) increase to 2.76 +/- 0.48 micromol min(-1) measured in untreated controls. Indo increased U(Na)V twofold, similarly in the clotrimazole and in the control group; in the absence or presence of clotrimazole treatment, COX blockade significantly decreased MBF and increased Y.
Conclusion: The data indicate that blockade of the CYP450 epoxygenase significantly impairs excretion of sodium in rats acutely loaded with hypertonic NaCl solution. The paradoxical post-Indo natriuresis is preserved in clotrimazole treated rats, which speaks against the role of CYP450 pathway in the response.