Regulation of the gene expression of preproenkephalin in the rat brain: influence of hemorrhage.

In the present study, we examined the expression of the gene encoding for the production of the opioid peptide enkephalin in specific brain regions during hemorrhage in the conscious rat. Rats were subjected to fixed-volume (8 ml/300 g) bleeding via jugular vein within 10 min. Total RNA was isolated from rat brain tissue using the hot phenol/chloroform method. Preproenkephalin transcript levels were quantified using Northern blot hybridization of total RNA with alpha-32P-labeled cDNA probe, and autoradiograms were scanned with a densitometer. The ppENK transcript in midbrain was significantly elevated following one and two hours of hemorrhage compared to control group (P < 0.01). The ppENK transcript in spinal cord was also significantly increased after two hours of hemorrhage, when compared with control group (P < 0.01). In the brainstem, ppENK transcript was significantly decreased after both 1 and 2 hr of hemorrhage compared with control values (P < 0.01). These results indicate that hemorrhage acutely changes levels of the transcript of ppENK in specific brain regions. It is possible that the changes in brainstem ppENK transcript may be a mechanism by which certain inhibitory effects of enkephalins on important brain cardiovascular regulatory centers are mediated.