The effects of extracts from neurosecretory cells in the anterior vena cava and pharyngo-ophthalmic vein upon the hearts of intact free-moving octopuses

Monoamines and the isolated auricle of sepia officinalis: are there β-like receptors in the heart of a cephalopod?

Pharmacological examinations of isolated auricles from Sepia officinalis were carried out to analyze the putative role of the monoaminergic transmitter/receptor system in the control of auricle function. In conjunction with histofluorescence studies and HPLC analyses, evidence of a double excitatory serotonergic and noradrenergic innervation of the auricles was obtained. Serotonin-induced positive chronotropic and inotropic effects were blocked by mianserin (5-HT1 and 5-HT2) but not by cyproheptadine (5-HT2). It is assumed that the auricular serotonin (5-HT) receptor represents a 5-HT1-like subtype and is not identical to the ventricular 5-HT receptor. Noradrenaline, adrenaline and dopamine evoked mainly positive chronotropic reactions and less prominent positive inotropic reactions. The potency range (pD2 frequency: noradrenaline 6.65 >> adrenaline 5.69 > dopamine 5.34; pD2 amplitude: noradrenaline 6.09 (greater than or equal to) adrenaline 5.91 > dopamine 5.33) indicates out that noradrenaline might be the effective neurotransmitter in vivo. The α -mimetics clonidine (α 2) and phenylephrine (α 1) induced positive chronotropic and inotropic effects, while the β-mimetics albuterol (β2>β1) and dobutamine (β1) revealed only positive inotropic reactions. The β-agonist isoprenaline mimicked the positive chronotropic effects of noradrenaline and induced the strongest positive inotropic effects of all the agonists tested. Urapidil (α 1) or phentolamine (α 1 and α 2) blocked only the positive chronotropic effects of noradrenaline and isoprenaline. The positive inotropic effects of isoprenaline could be blocked by the adenylate cyclase inhibitors MDL-12,330A or SQ-22, 536, which had no effect on the chronotropic effects of isoprenaline. These results suggest that two catecholaminergic receptors are present in the auricles of Sepia officinalis: an α -like adrenoreceptor mediating mainly chronotropic effects, and a β-like receptor which appears to mediate inotropic effects by activating the cyclic AMP pathway. These results suggest that the auricles exert a regulatory effect on ventricular performance.

Effects of biogenic amines and related agonists and antagonists on the isolated heart of the common cuttlefish Sepia officinalis L

1. Effects of noradrenaline and the related compounds adrenaline, dopamine, octopamine, tyramine, clonidine and isoprenaline were studied in isolated heart preparations from the cuttlefish Sepia officinalis L. 2. All analogues produced a positive inotropic affect, with noradrenaline being the most potent substance. The chronotropic effects of the tested compounds differed widely. 3. The action of substances of the phenylethanolamine group were not antagonized by propranolol but were partly antagonized by phentolamine. 4. Serotonin and its analogues also produced cardio-excitation. These effects were blocked by cyproheptadine but not by methysergide. 5. These results indicate the presence of two different receptors in the Sepia myocardium: one type reacting with noradrenaline most effectively and a second type being stimulated by serotonin.

Histochemical localization of cholinesterases and monoamines in the central heart of Sepia officinalis L. (Cephalopoda)

The central heart of the coleoid cephalopod, Sepia officinalis, was studied using acetylcholinesterase and fluorescence histochemistry. Using histo- and cytochemical reactions, acetylcholinesterase was localized in the axolemma and axoplasm of specific cardiac nerve fibres, as well as in the sarcolemma and within the sarcotubular system of the muscle cells. Butyrylcholinesterase exhibited a different distribution, being found only in the luminal trabecular muscle layer. Glyoxylic-acid-induced fluorescence indicated the presence of catecholamines (emission maximum, 470 nm) in cardiac nerve axons. These histochemical findings support the hypothesis that noradrenaline and/or dopamine and acetylcholine act antagonistically as natural transmitters. Fluorophores indicating the presence of serotonin were not observed. The present results are discussed in the light of previous pharmacological findings.

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.