Preproenkephalin A gene expression in rat pineal.

Preproenkephalin A (ppEnk) mRNA has been identified in extracts of rat pineal gland using oligonucleotides complementary to nonoverlapping regions of this mRNA. The mRNA has an apparent molecular size of 1.4 kb, equivalent to that found in rat brain. Slot-blot analysis, used to determine the relative amount of ppEnk mRNA in several tissues, demonstrated that the pineal contains 70% of the concentration of ppEnk mRNA found in the hypothalamus. Using a highly specific radioimmunoassay, rat pineals were demonstrated to contain approximately 3.5 pg methionine-enkephalin (Met-Enk) per gland. Following enzymatic digestion to release cryptic Met-Enk from larger molecular forms, pineals contained approximately 160 pg Met-Enk per gland. Gel filtration analysis of pineal extracts demonstrated that the peak of the cryptic Met-Enk has a molecular weight of 32 kDa (presumably proenkephalin). These results suggest that in rat pineal ppEnk gene products may contribute to pineal functioning.