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ANESTHETIC PHARMACOLOGY

Alphaxalone, a Neurosteroid Anesthetic, Inhibits Norepinephrine Transporter Function in Cultured Bovine Adrenal Medullary Cells

Takafumi Horishita^*, Kouichiro Minami^*, Nobuyuki Yanagihara, Munehiro Shiraishi^*, Takashi Okamoto^*, Yousuke Shiga^*, Susumu Ueno, and Akio Shigematsu^*

Departments of *Anesthesiology and Pharmacology, University of Occupational and Environmental Health, School of Medicine, Kitakyushu, Japan

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

We studied the effects of alphaxalone, a neurosteroid anesthetic, on norepinephrine transporter (NET) function in cultured bovine adrenal medullary cells and the effect of a bolus injection of alphaxalone on blood pressure and serum norepinephrine (NE) levels in anesthetized rats. Alphaxalone (10–100 µM) inhibited the desipramine-sensitive uptake of [³H]-NE by bovine adrenal medullary cells in a concentration-dependent manner. Eadie-Hofstee analysis of [³H]-NE uptake showed that alphaxalone increased the apparent Michaelis constant without altering the maximal velocity, indicating that inhibition occurred via competition for the NET. Alphaxalone inhibited the specific binding of [³H]-desipramine to plasma membranes isolated from bovine adrenal medulla. Scatchard analysis of [³H]-desipramine binding revealed that alphaxalone increased the apparent dissociation constant for binding without altering maximal binding, indicating competitive inhibition. Bolus IV administration of alphaxalone had little effect on blood pressure but slightly, and significantly, increased the serum NE levels in anesthetized rats. These findings suggest that alphaxalone competitively inhibits NET function by interfering with both desipramine binding and NE recognition on the NET in adrenal medullary cells and probably in sympathetic neurons.

IMPLICATIONS: Alphaxalone inhibited the desipramine-sensitive uptake of [³H]-norepinephrine (NE) by interfering with desipramine binding in bovine adrenal medullary cells. A bolus IV administration of alphaxalone slightly and significantly increased the serum NE levels in anesthetized rats. These findings suggest that alphaxalone competitively inhibits NE transporter function probably in sympathetic neurons.

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