Detection and quantitation of pro-opiomelanocortin mRNA in pituitary and brain tissues from different species.

Pro-opiomelanocortin-like mRNA has been detected in anterior and neurointermediate lobes of the pituitary, hypothalamus, amygdala, and cerebral cortex of rats by Northern blot analysis using a 144-base-pair DNA hybridization probe complementary to the beta-lipotropin domain of pro-opiomelanocortin mRNA. The hybridizing species of RNA in the pituitary lobes and hypothalmus is approximately 1100 bases long whereas that in the amygdala and cerebral cortex is 1000 bases long. Solution hybridization analysis with this same probe indicates that pro-opiomelanocortin mRNA is 20 times as concentrated in the neurointermediate lobe as in the anterior lobe of the pituitary. In turn, the pro-opiomelanocortin mRNA levels in the anterior pituitary are 1 to 2 orders of magnitude higher than those in the brain tissues. These results support the hypothesis that adrenocorticotropic hormone/endorphin peptides previously detected in the hypothalamus and amygdala with immunological techniques are synthesized in these tissues from a precursor similar to pro-opiomelanocortin in the pituitary.