This study investigated expression of prolactin receptor (PRL-R) mRNA in selected hypothalamic nuclei of lactating rats (days 7-10 post partum) compared with dioestrous rats. Rat brains were frozen with liquid nitrogen and cut into coronal sections of 300 µm. From these sections, tissues were micropunched from the parietal cortex (CTX), choroid plexus (ChP), and five hypothalamic regions: supraoptic (SO), paraventricular (Pa), arcuate (Arc) and ventromedial hypothalamic (VMH) nuclei, and median eminence (ME). Expression of both short and long forms of PRL-R mRNA were evaluated by reverse transcription-PCR and Southern hybridisation. The results showed that the relative amount of short form mRNA in the ChP of lactating rats was significantly higher than in dioestrous rats. The short form of PRL-R mRNA was undetectable in the SO, Pa, VMH of dioestrous rats but was expressed at a significant level in lactating rats. Levels of long form mRNA in the ChP, SO, Pa and VMH in lactating rats were significantly increased compared with dioestrous rats. Moreover, the long form mRNA was induced in the CTX of lactating rats. In the Arc, levels of both forms of PRL-R mRNA tended to increase in lactating rats compared with dioestrous rats but changes were not statistically significant. Neither form of PRL-R mRNA was detectable in the ME in the two animal models. Increased expression of PRL-R mRNA in specific brain regions during lactation is consistent with the variety of PRL effects on the brain, and may help to explain profound physiological changes in the lactating mother.

A comparison of the effects of magnesium valproate (MV) and sodium valproate (SV) on the action potential of isolated papillary muscle from guinea pigs and dogs was made in this study. The results in both animals were as follows: MV and SV induced a slight reduction of slope plateau of action potential and prolongation of action potential duration (APD). What is more, APD50 and APD90 were prolonged significantly, thus the ratio of APD90/APD25 was increased. The effective refractory period (ERP) was prolonged significantly. MV or SV showed no effects on action potential amplitude, overshoot, resting potential and phase 0 upstroke velocity. The above results suggested that MV and SV might play an antiarrhythmic role and that their effects were analogic. The mechanism of MV and SV inducing significant prolongation of APD50, APD90, and ERP, might be closely related to the slow-down of the velocity of K+ efflux during plateau and repolarization of phase 3 by radical of valproate and the slow-down of velocity of K+ efflux of repolarization of phase 3 in particular. These results showed that there was no difference in SV and MV action on guinea pigs and dogs.