Oxaprotiline enantiomers given repeatedly and brain α-adrenoceptors

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Abstract
The influence of (+)- and (−)-oxaprotiline (OXA) given repeatedly on the behavioural effects mediated by α1 and α2-adrenoceptors as well as on the binding to brain α1-adrenoceptors was studied. (+)-OXA given repeatedly for 14 days (but not 3 or 7 days) enhanced exploratory hyperactivity of rats induced by methoxamine injected intracerebroventricularly; (−)-OXA given for 3, but not 7 or 14 days, increased the methoxamine-induced exploration in rats. The locomotor hyperactivity induced in mice by d,1-threo-3,4-dihydroxyphenylserine was increased by repeated (14 days) (−)-OXA but not (+)-OXA. Neither OXA enantiomers given repeatedly modified the clonidine-induced locomotor hypoactivity in mice. Both enantiomers given repeatedly did not change the binding of [3H] prazosin to aradrenoceptors (Bmax, KD) in the thalamus and hippocampus. Repeated (+)-OXA increased the affinity of α1adrenoceptors for phenylephrine in the cortex, thalamus and hippocampus. A similar effect of (−)-OXA was observed in the hippocampus only. The results indicate that both OXA enantiomers are able to enhance the responsiveness of brain α1-adrenergic system, probably via the increase in the affinity of α1-adrenoceptors for their agonists.

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