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ANESTHETIC PHARMACOLOGY

Tramadol Has No Effect on Cortical Renal Blood Flow—Despite Increased Serum Catecholamine Levels—in Anesthetized Rats: Implications for Analgesia in Renal Insufficiency

Etsuko Nagaoka, MD^*, Kouichiro Minami, MD PhD^*, Yohsuke Shiga, MD^*, Yasuhito Uezono, MD PhD, Munehiro Shiraishi, MD^*, Kazuyoshi Aoyama, MD PhD^*, and Akio Shigematsu, MD PhD^*

*Department of Anesthesiology, University of Occupational and Environmental Health, School of Medicine, Kitakyushu, Japan; and Department of Second Pharmacology, Nagasaki University, School of Medicine, Nagasaki, Japan

Address correspondence and reprint requests to Kouichiro Minami, MD, PhD, Department of Anesthesiology, University of Occupational and Environmental Health, Japan, School of Medicine, 1-1 Iseigaoka, Yahatanishi-ku, Kitakyushu, 807-8555, Japan. Address e-mail to kminami{at}med.uoeh-u.ac.jp

Tramadol is an analgesic that inhibits norepinephrine (NE) reuptake. Although NE released from renal sympathetic nerves causes renal hypoperfusion, the effects of tramadol on renal hemodynamics have not been well characterized. We investigated the effects of tramadol on renal blood flow (RBF), mean arterial blood pressure (MAP), and heart rate (HR) by using a laser Doppler flowmeter, both in normal anesthetized rats and in rats with experimentally-induced nephritis secondary to anti-Thy 1.1 antibody administration. We also studied the effects of tramadol on serum NE levels. Tramadol increased MAP and decreased HR without changing RBF in normal rats at clinical doses. Serum NE levels increased up to 176% of control after a 2 mg/kg bolus injection of tramadol. Continuously infused, increasing doses of tramadol (0.5–4 mg · kg^-1 · h^-1) did not affect MAP, HR, or RBF. Tramadol also increased MAP and decreased HR without changing RBF in rats with experimentally induced renal insufficiency. These findings suggest that a bolus injection of tramadol does not alter RBF, although it causes a decrease in HR and an increase in MAP and serum NE in both normal rats and in rats with renal insufficiency. These results suggest that tramadol may have little effect on RBF during the postoperative period.

IMPLICATIONS: A bolus and continuous injection of tramadol does not alter renal blood flow (RBF) in normal rats. A bolus injection of tramadol has little effect on RBF in rats with experimentally induced renal insufficiency. These results suggest that tramadol would be a safe analgesic for maintaining RBF during the postoperative period.

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