Evidence for a differential postnatal development of proenkephalin B (= prodynorphin)-derived opioid peptides in the rat hypothalamus.

[he concentrations of immunoreactive (ir-) peptides derived from the opioid peptide precursors proenkephalin A (Met-enkephalin), proenkephalin B [dynorphin (DYN)-(1-17), dynorphin-(1-8), dynorphin B, alpha-neoendorphin (alpha-NEO-E), beta-NEO-E] and proopiomelanocortin [beta-endorphin (beta-END)], and of the neurosecretory hormones vasopressin and oxytocin increased between approximately 10-fold and 50-fold from birth to adulthood in the rate hypothalamus. Gel filtration and HPLC analysis of proenkephalin B-derived opioid peptides revealed that in 3-day-old rats the predominant portion of ir-dynorphin-(1-17) and a substantial part of ir-dynorphin B consisted of a high (6000) mol wt species, a common precursor peptide for DYN-(1-17) and DYN B. In adults rats, however, authentic DYN-(1-17) and DYN B were found to be the major ir-forms. The mol wt patterns of ir-DYN-(1-8), ir-alpha-NEO-E and ir-beta-NEO-E did not differ between 3-day-old and adult rats and reflected predominantly the respective authentic opioid peptides. Taking into consideration the developmental changes in the mol wt pattern of ir-DYN-(1-17), authentic DYN-(1-17) was 5 times lower in concentration than DYN-(1-8) in 3-day-old rats, whereas in adults these opioid peptides occurred in equimolar concentrations. These findings suggest that the posttranslational processing of the precursor proenkephalin B changes in the course of postnatal development. Ir-beta-END in the hypothalamus of newborn and adult rats consisted exclusively of beta-END-sized peptides which were not (unlike those in the intermediate pituitary lobe) alpha-N-acetylated. Thus, in the hypothalamus, the enzymatic processing of the opioid peptide precursor proopiomelanocortin to beta-END seems to be fully active at birth, in contrast to that of proenkephalin B.