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D1-like dopamine receptor activation and natriuresis by nitrocatechol COMT inhibitors.. M A Vieira-Coelho; P Gomes; M P Serrão; P Soares-da-Silva (2001) Kidney international display abstract
BACKGROUND: In recent years, several nitrocatechol derivatives (tolcapone, entacapone, and nitecapone) have been developed and found to be highly selective and potent inhibitors of catechol-O-methyltransferase (COMT). More recently, natriuretic properties were described for two of these compounds (entacapone and nitecapone), although this was not accompanied by enhanced urinary excretion of dopamine. We hypothesized that nitrocatechol derivatives stimulate D1-like dopamine receptors. METHODS: Adult male Wistar rats were treated with a nitrocatechol COMT inhibitor (entacapone, tolcapone, or nitecapone, 30 mg/kg, orally), and the urinary excretion of dopamine and sodium was quantitated. The interaction of nitrocatechol derivatives with D1-like receptors was evaluated by their ability to displace [3H]-Sch23390 binding from membranes of rat renal cortex and cAMP production in opossum kidney (OK) cells. RESULTS: Urinary excretion of sodium (micromol/h) was markedly increased by all three nitrocatechol derivatives: vehicle, 55.0 +/- 5.6; entacapone, 98.4 +/- 9.3; tolcapone, 97.5 +/- 9.3; and nitecapone, 120.5 +/- 12.6. Pretreatment with the selective D1 antagonist Sch 23390 (60 microg/kg) completely prevented their natriuretic effects. Nitecapone and tolcapone were equipotent (IC50s of 48 and 42 micromol/L) and more potent than entacapone and dopamine (IC50s of 107 and 279 micromol/L) in displacing [3H]-Sch23390 binding. In OK cells, all three nitrocatechol derivatives significantly increased cAMP accumulation and reduced Na(+)/H(+) exchange and Na(+),K(+)-ATPase activities, this being prevented by a blockade of D1-like receptors. CONCLUSION: Stimulation of D1-like dopamine receptors and inhibition of Na(+)/H(+) exchange and Na(+),K(+)-ATPase activities by nitrocatechol COMT inhibitors may contribute to natriuresis produced by these compounds.
Different modes of action of catecholamine-O-methyltransferase inhibitors entacapone and tolcapone on adenylyl cyclase activity in vitro.. M Gerlach; W Ukai; H Ozawa; P Riederer (2002) Journal of neural transmission (Vienna, Austria : 1996) display abstract
Catechol-O-methyltransferase (COMT) inhibitors such as entacapone and tolcapone are used as adjuncts to L-DOPA ( l-3,4-dihydroxyphenylalanine, levodopa) in the treatment of Parkinson's disease. Tolcapone has been reported to associate with diarrhoea, a common reason for study withdrawal. The mechanism of this adverse effect is not yet understood. Cholera toxin causes diarrhoea by permanent activation of G(s) proteins, resulting in increased adenylyl cyclase (AC) activity. The aim of this study was to examine the effects of the COMT inhibitors entacapone and tolcapone on AC activity in membranes isolated from rat striatum, a brain structure enriched with dopaminergic G-protein-coupled receptors and AC activity. This study demonstrates differential effects of tolcapone and entacapone on Gpp(NH)p/dopamine-stimulated AC activity. Entacapone enhanced the stimulatory effect of Gpp(NH)p/dopamine, whereas tolcapone attentuated this effect, suggesting that diarrhoea associated with tolcapone treatment is not caused by permanent activation of G(s) proteins.
Early administration of entacapone prevents levodopa-induced motor fluctuations in hemiparkinsonian rats.. C Marin; E Aguilar; M Bonastre; E Tolosa; J A Obeso (2005) Experimental neurology display abstract
The purpose of this study was to investigate the effect of the catechol-O-methyltransferase (COMT) inhibitor, entacapone, in the reversal and prevention of "wearing-off" phenomena in hemiparkinsonian rats. Catechol-O-methyltransferase (COMT) inhibitors increase the half-life and bioavailability of levodopa, providing more continuous dopamine receptor stimulation. This raises the possibility of using levodopa and a COMT inhibitor not only to treat motor complications, but also to prevent their development. Male Sprague-Dawley rats received a unilateral 6-hydroxydopamine (6-OHDA) administration in the nigrostriatal pathway. Two sets of experiments were performed. First, animals were treated with levodopa (50 mg/kg/day with benserazide 12.5 mg/kg/day, twice daily (b.i.d.), intraperitoneally (i.p.) for 22 days. On day 23, animals received either entacapone (30 mg/kg, i.p.) or vehicle with each levodopa dose. In the second set, animals were treated either with levodopa (50 mg/kg/day, i.p.) plus entacapone (30 mg/kg/day, i.p.) or levodopa (50 mg/kg/day, i.p.) plus vehicle, administered two or three times daily [b.i.d. or thrice daily (t.i.d.), respectively] for 22 consecutive days. Entacapone both reversed and prevented the shortening of the motor response duration that defines "wearing-off" motor fluctuations. Entacapone also decreased the frequency of failures to levodopa. The combination of levodopa and entacapone may reduce the likelihood of motor fluctuation development and may thus become a valuable approach to treat Parkinson disease whenever levodopa is needed.