Rat strain differences in responses of plasma prolactin and PRL mRNA expression after acute amphetamine treatment or restraint stress

1. The aim of this study was to compare the effects of acute amphetamine (A MPH) treatment and restraint stress on plasma level of prolactin (PRL) and PRL mRNA expression in the adenohypophysis in Sprague-Dawley and Lewis male rats, the latter known to have a deficient hypothalamo-pituitary-adrenal ( HPA) axis. 2. Both restraint stress and AMPH treatment (i.p. in a dose of 8 mg/kg of b .w.) were applied 15 or 30 min before termination of the experiment. Plasma PRL and corticosterone (CORT) were determined by radioimmunoassay PRL mRNA expression was estimated by a dot-blot hybridization. 3. Restraint stress and AMPH treatment induced a significant increase in th e CORT plasma level, as an indicator of stress response. Compared to Spragu e-Dawley rats; the magnitude of CORT increase after both stimuli was signif icantly lower in Lewis rats. 4. Although restraint stress significantly increased the PRL plasma levels in both rat strains, AMPH treatment reduced the PRL levels in both rat stra ins. However, the changes of PRL plasma levels had another pattern in Lewis rats than in Sprague-Dawley rats. Control plasma PRL levers were significa ntly higher in Lewis rats, and in this rat strain AMPH treatment for 30 min increased the PRL levels as compared to the values obtained after AMPH tre atment for 15 min. 5. Expression of PRL mRNA in adenohypophysis by restraint stress and AMPH t reatment had a similar pattern. After a 35-min lasting restraint stress, th e expression of PRL mRNA was decreased insignificantly in both rat strains. AMPH treatment induced in Sprague-Dawley rats a significant decrease of PR L mRNA after a 15-min interval while after 30 min there was a significant i ncrease. However, in Lewis rats AMPH failed to significantly change PRL mRN A. 6. The results from the present study indicate that the mechanisms mediatin g the effects of acute restraint stress and acute AMPH treatment differ in PRL response in Sprague-Dawley and Lewis male rat strains. Differences in t he observed responses in Lewis rats could be related to the deficient activ ity of HPA axis in this rat strain.