Cardiac synthesis, processing, and coronary release of enkephalin-related peptides

Although preproenkephalin mRNA is abundant in the heart, the myocardial syn thesis and processing of proenkephalin is largely undefined. Isolated worki ng rat hearts were perfused to determine the rate of myocardial proenkephal in synthesis, its processing into enkephalin-containing peptides, their sub sequent release into the coronary arteries, and the influence of prior symp athectomy. Enkephalin-containing peptides were separated by gel filtration and quantified with antisera for specific COOH-terminal sequences. Proenkep halin, peptide B, and [Met(5)]enkephalin-Arg(6)-Phe(7) (MEAP) comprised 95% of the extracted myocardial enkephalins (35 pmol/g). Newly synthesized enk ephalins, estimated during a 1-h perfusion with [C-14] phenylalanine (4 pmo l . h(-1) . g wet wt(-1)), were rapidly cleared from the heart during a sec ond isotope-free hour. Despite a steady release of enkephalins into the cor onary effluent (4 pmol . h(-1) . g wet wt(-1)), enkephalin replacement appa rently exceeded its release, and tissue enkephalins actually accumulated du ring hour 2. In contrast to the tissue, methionine-enkephalin accounted for more than half of the released enkephalin. Chemical sympathectomy produced an increase in total enkephalin content similar to that observed after 2-h control perfusion. This observation suggested that the normal turnover of myocardial enkephalin may depend in part on continued sympathetic influence s.