Dopamine receptor-mediated hypothermia induced in rats by (+)-, but not by (-)-3-PPP

The novel dopaminergic agents (+)- and (-)-3-PPP were evaluated for their effects upon thermoregulation in rats maintained at room temperature (approximately 22 degrees C). Although approximately 30 times less potent than apomorphine, (+)-3-PPP induced a clearcut, dose-dependent and haloperidol/pimozide-reversible hypothermia. In contrast, the (-)-enantiomer per se lacked a significant effect upon rat body temperature. However, (-)-3-PPP clearly attenuated apomorphine-induced hypothermia. Simultaneous biochemical investigations confirmed the presence of central dopamine (DA) agonist and antagonist properties for (+)- and (-)-3-PPP, respectively, at the doses employed. The results are compared to the agonist and antagonist effects of the 3-PPP enantiomers in various other central DA receptors systems. Particular reference is made to the recent hypothesis by Carlsson (J. Neural Transm. 57 (1983) 309, relating agonist intrinsic activity to the DA receptor responsiveness state, in turn determined by the endogenous tone. Based on the findings with (+)- and (-)-3-PPP it is suggested that DA receptors mediating hypothermia in the rat may be more akin to 'normosensitive' postsynaptic than to highly 'agonist-responsive' autoreceptors.