By means of an enzyme-linked immunosorbent assay, the concentration of enkephalin-immunoreactive substances was estimated to be about 25 nM in the chicken retina. The biosynthesis of 3H-Met5-enkephalin in this retina was studied by a pulse-chase incubation technique. Isolated retinas were incubated with 0.2 ml of oxygenated Ringer's solution containing 40 microCi of [3H]methionine and trasylol,...

Intact chromaffin granules isolated from bovine adrenal medulla were incubated at 37 degrees C for up to 22 hr. Processing of enkephalin-containing (EC) peptides in the granules was followed by the change in their size distribution as shown by chromatography on Sephadex G-75 columns. A gradual shift toward lower molecular weight EC peptides was observed during the incubation, indicating process...

Application of enkephalins to the luminal surface of the bowel augments intestinal absorption. However, to date, endogenous enkephalins have not been demonstrated within intestinal luminal fluid. To determine whether enkephalins are present in the intestinal lumen, five adult dogs had 25-cm chronic jejunal Thiry-Vella loops constructed. Dogs were studied in the awake, fasted state. Jejunal loop...

Intracellular recordings were made from layer V pyramidal neurons in slices of rat anterior cingulate cortex, using electrodes that contained potassium methylsulfate and biocytin. [Met5]enkephalin (300 nM to 30 microM) reversibly reduced the amplitude of EPSPs evoked by stimulation of the subcortical white matter; the half-maximal concentration was about 800 nM. These EPSPs were blocked by (+/-...

Enkephalin, a brain peptide with morphine-like activities, is rapidly inactivated by a membrane-associated aminopeptidase present in brain. Evidence presented here suggests that enkephalin binding to opiate receptors is coupled to subsequent aminopeptidase degradation. This conclusion is based upon the following observations. 1) Enkephalin degradation, at concentrations 4 orders of magnitude be...

Enkephalins have peripheral vascular effects, and enkephalinergic innervation of the heart has been reported. To determine whether enkephalins have direct effects on myocardium, we studied the effects of [D-Ala2, Met5]enkephalinamide and [D-Ala2, D-Leu5]enkephalin on amplitude of contraction (measured with an optical-video system) in spontaneously beating monolayer cultures of chicken embryo ve...

In cultured bovine chromaffin cells, changes in the dynamic state of enkephalin stores elicited experimentally were studied by measuring cellular proenkephalin mRNA, as well as enkephalin precursors and authentic enkephalin content of cells and culture media. In parallel, tyrosine hydroxylase mRNA and catecholamine cell content were also determined. Low concentrations (0.5-100 pM) of dexamethas...

The effects of Met-enkephalin on Ca2+-dependent K+ channel activity were investigated using the cell-attached patch recording technique on isolated parasympathetic neurones of rat intracardiac ganglia. Large-conductance, Ca2+-dependent K+ channels (BK(Ca)) were examined as an assay of agonist-induced changes in the intracellular free calcium ion concentration ([Ca2+]i). These BK(Ca) channels ha...

Transfer of an aqueous-soluble peptide hormone or neurotransmitter such as [Met]- or [Leu]enkephalin (Tyr1-Gly2-Gly3-Phe4-Met5(Leu5)), to the lipid-rich environment of its membrane-embedded receptor protein may convert the peptide into a ("bioactive") conformation required for eliciting biological activity. We have examined by high-resolution nuclear magnetic resonance (NMR) spectroscopy the co...