Enkephalin-related peptides: direct action on the octopus heart.
Immunocytochemical evidence for the occurrence of "vertebrate" peptides in the neuropil of the vena cava [12, 13] and the structural similarity between enkephalin precursor peptides and the molluscan cardioexcitatory peptide [16], lead us to study the action of enkephalin-related peptides on the octopus heart. Systemic hearts of Octopus vulgaris were perfused with sea wate and test substances and a crude extract of vena cave were added for 1 min; frequency and pressure were monitored continuously. The heptapeptide Leu5-enkephalin-Arg6-Phe7 and the Met5-analogue, both in the amidized form, displayed dose-response relationship with a sensitivity of about 10 nmol. The C-terminal tetrapeptide amides, Phe-Leu/Met-Arg-Phe-NH2, were active at the same doses. Opiate receptors do not seem to be involved in this action on the octopus heart, as naloxone treatment had no effect. Whereas the N-terminal portion of the heptapeptide is known to be crucial for activity as an opioid, the C-terminal NH2 group is essential for cardioexcitatory activity.
D000818:Animals; D004305:Dose-Response Relationship, Drug; D004723:Endorphins / Q000494:pharmacology*; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives*; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives; D004745:Enkephalins / Q000494:pharmacology*; D005260:Female; D006321:Heart / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D049831:Octopodiformes / Q000502:physiology*
D004723:Endorphins; D004745:Enkephalins; D009270:Naloxone; D004744:Enkephalin, Methionine; D004743:Enkephalin, Leucine; C028717:enkephalin-Met, Arg(6,7)-; C033460:enkephalin-Met, Arg(6)-PheNH2(7)-; C033458:enkephalin-Leu, Arg(6)-Phe(7)-; C033459:enkephalin-Leu, Arg(6)-PheNH2(7)-