Background: The causes for the nephrotoxicity of cyclosporine A (CsA) have not been fully elucidated. Intrarenal vasoconstriction induced by several different mediators, both in humans and experimental animals, have been proposed. Methods: We studied prostaglandin metabolites, endothelin and nitric oxide in kidney transplant patients receiving their first CsA dose. Prostaglandin metabolites in the urine and endothelin and nitric oxide (NO₂/NO₃) in urine and plasma were measured in 14 patients before and 3 and 6 h after oral ingestion of CsA (10 mg/kg b.w.). Clearances for inulin and p-aminohippuric acid (PAH) were measured before and in two separate 3-hour periods after CsA. Blood pressure, heart rate, and CsA blood levels were also determined. Results: Clearances of inulin and PAH decreased progressively after CsA dosage while renal vascular resistance increased. Nitric oxide plasma levels decreased in nearly all patients from 21.0 ± 2.8 to 19.1 ± 2.6 (p = 0.003) and then rose slightly to 19.5 ± 2.5 µmol/l (p = 0.1) 3 and 6 h after CsA ingestion, respectively. Urinary excretion of NO₂/NO₃ decreased nonsignificantly from 269 ± 38.8 to 259 ± 27.7 and 254 ± 41.6 µmol/min (p = 0.5 and 0.5). At the same time, urinary prostaglandin E₂ and 6-keto-prostaglandin F_1α excretion rate declined significantly [from 1,187 ± 254 to 1,186 ± 351 and 730 ± 148 pg/min (p = 0.27 and 0.02) and from 697 ± 115 to 645 ± 134 and 508 ± 58.2 pg/min (p = 0.34 and 0.05)]. Urinary thromboxane B₂ and plasma and urinary endothelin first increased and then decreased nonsignificantly. Mean arterial pressure rose from 107 ± 2.5 to 110 ± 2.6 and 114 ± 3.4 mm Hg (p = 0.1 and 0.05). Conclusion: The pathophysiology of CsA-induced acute renal vasoconstriction involves several different mechanisms including a decrease of the vasodilating prostaglandins E₂ and 6-keto-prostaglandin F_1α and possibly nitric oxide.

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