R. de Castiglione

RELATIVE POTENCY OF BOMBESIN‐LIKE PEPTIDES

1 The pharmacological activity of two natural bombesin‐like peptides, alytesin and litorin, and 25 related synthetic peptides has been compared to that of bombesin. 2 The minimum length of the amino acid chain required for the first appearance of bombesin‐like effects was represented by the C‐terminal heptapeptide, and the minimum length for maximal effects by the C‐terminal nonapeptide. The latter possessed approximately the same activity as bombesin and may be considered a good substitute. 3 Both the tryptophan and histidine residues seemed to be essential for bombesin‐like activity. 4 The C‐terminal octapeptide was less active than either bombesin or the C‐terminal nonapeptide and its action was more rapid in onset and less sustained. 5 Litorin apparently has an intermediate position between bombesin octapeptide and bombesin nonapeptide in the speed and duration of its effects. The relationship between structure and activity is discussed.

Phyllomedusa skin: A huge factory and store-house of a variety of active peptides

The skin of the neotropical hylid frogs belonging to the subfamily. Phyllomedusinae is a formidable factory and store-house of a variety of active peptides belonging to seven distinct families: the caeruleins (represented by phyllocaerulein), the bradykinins (phyllokinin), the tachykinins (phyllomedusin), the bombesins (phyllolitorin, [Leu8]phyllolitorin, rohdei-litorin), sauvagine, the dermorphins (dermorphin, [Hyp6]dermorphin) and finally the tryptophyllins (a set of 8-11 members). Another linear peptide and three diketopiperazines should be added to the list. The biochemical and pharmacological positions of the Phyllomedusa peptides within their families is briefly discussed, dwelling upon some recent and controversial data.

Synthetic peptides related to the dermorphins. I. Synthesis and biological activities of the shorter homologues and of analogues of the heptapeptides

Dermorphins are potent opiate-like peptides isolated from the skin of some species of frogs. They are characterized by the presence of a D-amino acid residue, which is crucial for bioactivity. A number of analogues were prepared in order to evaluate the structure-activity relationships. The syntheses were accomplished either by conventional or solid-phase procedures. In vitro assays included both guinea pig ileum (GPI) and mouse vas deferens (MVD) preparations. Central analgesic (tail-flick and hot plate tests) and cataleptic activities were determined in the rat by intracerebroventricular route. The potency of dermorphin (H- Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2) in the different tests was: GPI: IC50 = 3.3 nM; MVD: IC50 = 29 nM; hot plate: ED50 = 13.3 pmol/rat; tail-flick: ED50 = 23 pmol/rat; catalepsy: ED50 = 130 pmol/rat.

Sauvagine, a new polypeptide from Phyllomedusa sauvagei skin

Summary1.The occurrence of sauvagine, a new polypeptide from amphibian skin, and its actions on rat blood pressure and diuresis were studied.2.Sauvagine was found to be present in the skin of all the 10 Phyllomedusa species so far studied, amounts ranging from a few micrograms to 240 μg per g fresh skin.3.The polypeptide displayed in the rat an intense, long-lasting hypotensive action accompanied by tachycardia. Hypotension was not modified by either atropine or propranolol, excluding the participation of the autonomic nervous system in its production. Tachycardia, on the contrary, was partially inhibited by propranolol.4.Hypotension is probably the main cause of the intense antidiuresis seen in hydrated rats following sauvagine administration. Reduction in urina volume was accompanied by a decrease in GFR and an increase in tubular Na+ reabsorption.

Opioid receptor binding profile of selected dermorphin-like peptides

The receptor binding profile of a selected group of dermorphin-like peptides was determined and correlated with the results of the guinea pig ileum (GPI) and mouse vas deferens (MVD) bioassays and with the currently used antinociception tests in the rat. For the peptides with the characteristic dermorphin D-Ala2-Phe3-Gly4 sequence, a linear negative correlation was found between the reciprocal of sodium shift and relative affinity for the mu-type opioid receptor. For the same peptides, a positive correlation was evidenced between relative potency on GPI and MVD and relative affinity for mu- and delta-type receptors, respectively.

Antinociceptive, prolactin releasing and intestinal motility inhibiting activities of dermorphin and analogues after subcutaneous administration in the rat

A series of analogues and shorter homologues of dermorphin (DM), a frog skin heptapeptide with potent morphine-like activity, have been assayed in the rat after subcutaneous (SC) administration at the screening dose of 4 mg/kg. The effects taken into account are: analgesia (tail-pinch test), stimulation of prolactin (PRL) secretion, and inhibition of gastro-intestinal (GI) motility (charcoal meal transit). Effective doses were calculated for the most active compounds. The potency of DM (H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2) in the different tests was: tail-pinch: ED50 = 0.83 mg/kg; PRL release: ED100 = 0.3 mg/kg; inhibition of GI motility: ED30 = 1.8 mg/kg.

Synthetic peptides related to the dermorphins. II. Synthesis and biological activities of new analogues

A new series of analogues of the potent opiate-like peptides dermorphins (mainly tetra- and pentapeptides) were synthesized in order to better evaluate the structure-activity relationships. Relative potencies were referred to dermorphin (H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2), the prototype of this class of frog skin peptides. Peripheral opioid activity (guinea-pig ileum and mouse vas deferens) was determined for all the dermorphin analogues. For a selected number of them also central analgesic (hot plate and tail-flick tests) and cataleptic activities were assayed in the rat by intracerebroventricular administration.

EFFECT OF SUBSTANCE P AND ITS NATURAL ANALOGUES ON GASTRIC EMPTYING OF THE CONSCIOUS RAT

1 Substance P and its natural analogues were tested for their effect on gastric emptying in the rat. 2 Substance P and kassinin were virtually inactive even at the maximum dose tested. 3 The other tachykinins significantly delayed gastric emptying, their effect being quite remarkable with 100 μg/kg. The lowest doses (30 μg/kg) caused a slight and non‐significant increase in emptying rate. 4 The effect on gastric emptying was most probably correlated with a spasmogenic effect on the gastroduodenal junction, as pointed out in previous work.

Antinociceptive and other opioid effects of a new series of dermorphin analogues after subcutaneous administration in the rat

A series of hepta-, hexa-, penta- and tetrapeptide analogues of dermorphin have been evaluated in the rat for antinociceptive activity after subcutaneous (SC) administration at the screening dose of 4 mg/kg. Effective doses (ED50) were calculated for the most active compounds. Presence of spontaneous movements, defecation, micturition and corneal reflex were also recorded. Syntheses and analytical data of new derivatives are briefly reported.

Structural requirements of ceruletide-like peptides for activity on gut and brain.

Abstract A series of ceruletide analogues were tested in order to evaluate the structural requirements for activity on gut and brain. The effects studied were: contraction of the guinea pig gallbladder and stimulation of the exocrine pancreatic secretion in the dog after intravenous (IV) administration, for activity on the gut; analgesia (hot plate test) and sedation (reduction of spontaneous rearing activity) in mice by subcutaneous (SC) route, for activity on the brain. The structural requirements were roughly the same for central and peripheral activities. Possible mechanisms for the antinociceptive effects of ceruletide in humans were proposed.