Met5-enkephalin-arg6-phe7 and its receptor in lung.

The presence of met5-enkephalin-arg6-phe7 (YGGFMRF) and opiate receptors in rat, guinea pig and human lung was investigated with specific and sensitive radio immuno- and radio-receptor assays. 1) High and low molecular weight YGGFMRF-like immunoreactivity were detected in lung extracts using Bio-Gel P-2 column chromatography followed by radioimmunoassay. Using HPLC, we determined that the low molecular weight YGGFMRF-like immunoreactivity is authentic YGGFMRF. 2) The contents of YGGFMRF were 0.68 +/- 0.08, 0.76 +/- 0.12 and 0.63 pmol/mg protein in lung of rat, guinea pig and human, respectively. In the lung of these three species, the content of YGGFMRF is much greater than that of met5-enkephalin. 3) 47 mM KCl released YGGFMRF from rat lung slices in a Ca++ dependent manner. 4) Rat lung membranes were shown to bind [3H]-etorphine in a saturable manner. There are two populations of binding sites with a Kd = 0.6 and 7.1 nM and a Bmax = 7.8 and 28.5 fmol/mg protein, respectively. This binding could be displaced by YGGFMRF with high affinity, the other endogenous opioid peptides were poor displacers. From these results, we infer that YGGFMRF might be a putative neurotransmitter or neuromodulator, its role in the regulation of lung function can now be investigated.