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INDOMETHACIN REVERSES LOCOMOTOR DEFICIT AND REDUCES BRAIN LEVELS OF NEUROINHIBITORY STEROIDS IN RATS FOLLOWING PORTACAVAL ANASTOMOSIS

S Ahboucha¹, W Jiang¹, N Chatauret¹, G Baker², RF Butterworth¹
¹Neuroscience Research Unit, Saint-Luc Hospital (CHUM), Montreal, Quebec; ²Neurochemical Research Unit, University of Alberta, Edmonton, Alberta

Hepatic encephalopathy (HE) is a neuropsychiatric complication of acute and chronic liver failure characterized by progressive neuronal inhibition. Neurosteroids (NS) such as the 3alpha-5alpha-reduced metabolites of progesterone are potent positive allosteric modulators of the GABA-A receptor complex (GRC), and "increased GABAergic tone" has been proposed and supported by several studies in experimental HE. Human and experimental models of HE showed that components of the "peripheral-type" benzodiazepine receptors, implicated in the synthesis of NS, are up-regulated, and a neuroinhibitory progesterone metabolite allopregnanolone (Allo) was recently shown to accumulate in brains of patients who died in hepatic coma. Brain levels of neuroinhibitory steroids Allo and the tetrahydrodeoxycorticosterone (THDOC) in a chronic model of HE following portacaval anastomosis (PCA) were measured using the technique of GC/MS. The functional status of the GRC was assessed with a radiometric assay using ³H-muscimol. Locomotor performance was monitored using an auto-track system. A significant accumulation of Allo (1.7-fold), THDOC (4.7-fold), as well as NS precursor pregnenolone (Preg, 2.6-fold) was observed in brain of PCA rats. The NS site on the GRC was unaltered. Brain accumulation of Allo and THDOC were in the nM range known to affect GRC, and brain extracts from PCA rats increase significantly the binding of ³H-muscimol, suggesting that brain accumulation of inhibitory NS in these animals are relevant to interact with components of GRC. Indomethacin (Indo); a 3-alpha hydroxysteroid dehydrogenase inhibitor implicated in the synthesis of Allo and THDOC, attenuated dose-dependently (0.1-5 mg/kg) the locomotor deficit of PCA rats, and normalized brain levels of Allo and THDOC. Effects of Indo were not mimicked by other cyclooxygenase inhibitors diclofenac or roficoxib suggesting that Indo effects are not mediated via the prostaglandin pathway. Increased circulating concentrations of THDOC (7-fold) but not Allo or Preg were observed in PCA rats suggesting that a peripheral source may contribute to brain accumulation of this NS. Increased brain levels of neuroinhibitory steroids offers a cogent explanation for the notion of "increased GABA-ergic tone" in HE. The use of agents that either inhibit NS synthetic enzymes or modulate the NS site on the GRC offer new therapeutic approaches for the management of chronic HE.
Funded by CIHR. SA is recipient of a CASL research fellowship

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