Enhancement of benzodiazepine binding by methaqualone and related quinazolinones. Drug Dev. Res. 7 :
Methaqualone and mecloqualone were found to inhibit [3H]diazepam binding to rat cortical membranes, whereas a related quinazolinone, piriqualone (3-(2-methylphenyl)-2-[2-(2-pyr- idinyl)ethenyl]-4(3H)-quinazolinone), elicited an increase in the binding. Irrespective of their in vitro effects on benzodiazepine binding, all three quinazolinones enhanced the amount of intravenously administered [3H]flunitrazepam bound to mouse brain in vivo. Ex vivo experiments indicated that the enhanced binding induced by methaqualone and piriqualone, as well as that elicited by the pyrazolopyridine binding enhancers cartazolate and tracazolate, involved an increase in receptor density. This ex vivo effect differed from the in vitro enhancement of [3H]diazepam binding by piriqualone, cartazolate, and tracazolate, which was caused by an increase in binding affinity, and the in vitro inhibition of binding by methaqualone. The quinazolinones did not appear to affect [3H]GABA binding, but GABA-like activity was suggested by their potent reversal of the cerebellar cyclic GMP accumulation induced by isoniazid. The benzodiazepinelike actions (anticonvulsant, hypnotic, anxiolytic) exerted by methaqualone and related quinazolinones may be mediated via GABAlbenzodiazepinelbarbiturate receptor complexes. -268, 1986.
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