Giovanna Improta

The Tachykinin Peptide Family

The tachykinin peptide family certainly represents one of the largest peptide families described in the animal organism. So far, more than 40 tachykinins have been isolated from invertebrate (insects, worms, and molluscs), protochordate, and vertebrate (skin, gastrointestinal tract, peripheral and central nervous system) tissues. Substance P (SP), first identified by bioassay as early as 1931 but sequenced only in 1971, several years after the elucidation of the structure of eledoisin from molluscan tissues and of physalaemin from amphibian skin, may be considered as a prototype of the tachykinins. Hitherto, as many as 19 tachykinins have been isolated from amphibian integument, and eight additional peptides have been isolated from amphibian gut and brain. Counterparts of skin tachykinins in mammalian tissues are SP, neurokinin A, and neurokinin B. Three main receptor subtypes for the tachykinins have been identified (NK1, NK2, and NK3), but their number is probably destined to increase. It is obvious that the peripheral and central effects of the tachykinins may substantially vary depending on the activation of different receptor subtypes. Matters are further complicated by the frequent capacity of the single tachykinins to bind, although with different affinity, to more receptors. It has been recognized that tachykinins have a variety of effects in physiological and pathological conditions, and there is evidence suggesting intrinsic neuroprotective and neurodegenerative properties of these neuropeptides. This review provides an update on the current body of knowledge regarding tachykinin occurrence and distribution in the animal kingdom, from the lowest invertebrates to man, and the physiological and pharmacological actions of tachykinins outlining the pregnant importance of this large peptide family.

PHARMACOLOGICAL DATA ON DERMORPHINS, A NEW CLASS OF POTENT OPIOID PEPTIDES FROM AMPHIBIAN SKIN

1 Dermorphin and Hyp6‐dermorphin are the first representatives of a new class of potent opioid peptides occurring in amphibian skin. They present the unique feature of having a D‐Ala residue incorporated in the peptide molecule. 2 Dermorphin displayed a potent depressive action on electrically stimulated contractions of the guinea‐pig ileum and mouse vas deferens preparations. Dermorphin was respectively 57,294, 18 and 39 times more potent than Met‐enkephalin, Leu‐enkephalin, β‐endorphin, and morphine on the guinea‐pig ileum opiate receptors. On the vas deferens receptors, dermorphin was about as potent as the enkephalins and 40 times more potent than morphine. Naloxone was a powerful antagonist to dermorphin in both preparations. 3 Dermorphin produced potent and long‐lasting analgesia in mice by intravenous injection, and in rats by intracerebroventricular injection, the ED50 being here of the order of 13–23 pmol/rat. Morphine was 752 and 2170 times less potent, depending on the analgesia test used. At high intracerebroventricular doses analgesia was accompanied by catalepsy. 4 Intracerebroventricular infusion of dermorphin induced development of tolerance and precipitation of withdrawal symptoms upon administration of naloxone. Both tolerance and physical dependence were consistently less marked with dermorphin than with morphine. 5 The minimum sequence requirement for full dermorphin activity was represented by the N‐terminal tetrapeptide. The presence of the D‐Ala2 residue was of crucial importance.

The brain-gut-skin triangle: New peptides

New data on tachykinins and bombesins are displayed and the present situation of research on the novel amphibian skin peptides sauvagine and dermorphin is illustrated. The potent stimulant effect of sauvagine on ACTH and beta-endorphin release has been confirmed both in vivo and on columns of isolated and dispersed rat pituitary cells, and similarly the potent inhibitory effect on PRL and GH release, both in the rat and man. Particular emphasis is laid on the occurrence of sauvagine-like immunoreactivity in fish urophysis and in amphibian nervous structures, including the retina. It is suggested that the long-searched corticotropin releasing factor and PRL release-inhibiting factor may be a sauvagine-like peptide. Dermorphin, in its turn, has been found to cause, by intracerebroventricular injection, not only analgesia and catalepsy, but also conspicuous EEG and behavioral changes in the rabbit and chick, as well as a sharp reduction in gastric emptying time and gastric acid output in the rat, together with marked stimulation of PRL release.

EVIDENCE OF CHOLECYSTOKININ RELEASE BY BOMBESIN IN THE DOG

1 The intravenous infusion of bombesin elicited in the dog a contraction of the gall bladder with decreased opening pressure of the choledocho‐duodenal junction and stimulation of pancreatic secretion. 2 The pancreatic juice produced under the influence of bombesin was poor in bicarbonate and rich in protein. Threshold doses of the peptide were of the order of 0.25 μg kg−1 h−1 and maximum protein output was obtained with 1 μg kg−1 h−1. The pancreatic protein response to bombesin was very similar, in its onset and duration, to that elicited by intraduodenal infusion of l‐tryptophan. Infusions of bombesin repeated at short intervals produced tachyphylaxis. 3 Antrectomy did not affect the stimulant action of bombesin on the pancreas. Atropine however, reduced the pancreatic protein response to bombesin. 4 It is suggested that bombesin acts on the gall bladder and the exocrine pancreas through release of cholecystokinin from the duodenal mucosa. No release of secretin could be demonstrated. It is likely that the releasing activity of bombesin is limited, in the field of gastrointestinal peptides, to those belonging to the gastrin‐cholecystokinin family.

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.

Central effect of SNC 80, a selective and systemically active δ-opioid receptor agonist, on gastrointestinal propulsion in the mouse

We investigated the effects of SNC 80 ((+)-4-[alphaR)-alpha-((2S,5R)-4-ally1-2,5-dimethyl-1-pipera zinyl)-3-methoxybenzyl]-N,N-diethylbenzamide), a new highly selective, non-peptidic and systemically active delta-opioid receptor agonist, on gastrointestinal and colonic propulsion in mice. Intraperitoneally (i.p.) SNC 80 (1, 10 and 30 mg/kg) significantly decreased gastrointestinal propulsion measured as transit of an orally administered charcoal meal. Pretreatment with the delta-opioid receptor antagonist, naltrindole (1 mg/kg) subcutaneously (s.c.), with the non-selective opioid antagonist, naloxone (5 mg/kg, s.c.) or the mu1-opioid receptor antagonist, naloxonazine (10 mg/kg, i.p.), significantly decreased the antitransit effect of SNC 80 but pretreatment with the non-selective opioid antagonist, naloxone methiodide (5 mg/kg, s.c.), a quaternary salt of naloxone that does not cross the blood-brain barrier, did not. SNC 80 (1, 5 and 10 mg/kg, i.p.), produced dose-related inhibition of colonic propulsion measured as the increase in mean expulsion time of a 3 mm glass bead placed in the distal colon. Naloxone (5 mg/kg, s.c.) and naltrindole (1 mg/kg, s.c.), completely antagonized the colonic antipropulsive effect of SNC 80. In contrast, naloxone methiodide (5 mg/kg, s.c.), left the inhibitory effect of i.p. SNC 80 on colonic function unchanged. These results suggest that peripherally injected SNC 80 inhibits gastrointestinal transit and colonic propulsion. It does so mainly through a central mechanism. Although the gastrointestinal antitransit effect of SNC 80 is naltrindole- and naloxonazine-sensitive, we cannot exclude an opioid-independent mechanism. The colonic antipropulsive effect of SNC 80 confirms the inhibitory role of the central delta-opioid receptor system on colonic motility.

Antidiarrheal and colonic antipropulsive effects of spinal and supraspinal administration of the natural δ opioid receptor agonist, [D-Ala2]deltorphin II, in the rat

The ability of the natural selective delta opioid receptor agonist, [D-Ala2]deltorphin II (DADELT II), to inhibit the diarrhea induced by castor oil and colonic glass bead expulsion, was studied in rats after supraspinal and spinal administration. When injected intracerebroventricularly, DADELT II (0.2, 1, 10 micrograms/rat) inhibited diarrhea and colonic bead expulsion in a dose-related fashion but did not affect the rate of small intestine transit. Similar results were obtained when the same dose of DADELT II was administered spinally. The antidiarrheal and colonic antipropulsive effects of supraspinally and spinally DADELT II were partially or completely antagonized by subcutaneous pretreatment with 1 and 10 mg/kg, respectively, of naltrindole, a selective delta opioid receptor antagonist. These findings indicate that, in the rat, supraspinal and spinal delta opioid receptors play a role in modulating diarrhea and colonic propulsion and that DADELT II is a useful tool for investigating the role of the delta opioid system in gastrointestinal function.

Distribution and metabolism of dermorphin in rats

Dermorphin distribution and metabolism were studied in rats injected with high doses of the peptide and with 125I-dermorphin, using RIA methods, HPLC extraction and -counting. Dermorphin rapidly disappeared from plasma (half-life: 1.3 min). In vivo and in vitro experiments demonstrated that the peptide was destroyed in liver and kidney. The highest percent (11%) of injected dermorphin has been found in the bile collected over 1 hour. HPLC analysis showed that bile contained also breakdown products (di, tri, and tetra N-terminal peptide fragments). Reported data suggested that intact dermorphin can be eliminated more slowly than breakdown products.

Peripheral anti-nociceptive effect of nociceptin/orphanin FQ in inflammation and stress-induced colonic hyperalgesia in rats

ABSTRACT Nociceptin/orphanin FQ (N/OFQ) and its NOP receptors are present in the central nervous system and in the periphery playing important roles in the modulation of gastrointestinal functions and pain. The aim of this study was to investigate the role of central and peripheral N/OFQ–NOP receptor system in the nociceptive response to colorectal distension (CRD) in basal condition and in two models of gut hypersensitivity triggered by both inflammation and stress. Male Wistar rats were tested in basal and in post‐inflammatory conditions, i.e., 5 days after IC TNBS instillation (80 mg/Kg) and received N/OFQ (2 nmol/Kg IP), UFP‐101 (a selective NOP receptor antagonist, 10 nmol/Kg IP), N/OFQ+UFP‐101, N/OFQ (0.5 nmol/rat ICV) or vehicle. Female rats were tested in basal and after partial restraint stress receiving the same pharmacological treatment. CRD was performed using barostat and abdominal contractions were recorded by electromyography. In basal condition, N/OFQ, ICV and IP injected, did not modify basal visceral sensitivity. Both in TNBS and stress‐induced hyperalgesia, IP but not ICV injection of N/OFQ significantly decreased the number of abdominal contractions. Peripheral injection of UFP‐101 antagonized N/OFQ effect. Moreover, in post‐inflammatory colitis, UFP‐101, injected alone, exacerbated visceral hyperalgesia to CRD compared with vehicle. These findings indicate that in rats, N/OFQ, only peripherally injected, reduces visceral hypersensitivity triggered by inflammation or stress without affecting basal sensitivity. N/OFQ visceral anti‐hyperalgesic effect involves peripheral NOP receptors. In a post‐inflammatory, but not in an acute stress colitis model, N/OFQergic system is endogenously activated.

In vitro and in vivo pharmacological role of TLQP-21, a VGF-derived peptide, in the regulation of rat gastric motor functions.

Background and purpose:  Vgf gene expression has been detected in various endocrine and neuronal cells in the gastrointestinal tract. In this study we investigated the pharmacological activity of different VGF‐derived peptides. Among these, TLQP‐21, corresponding to the 556–576 fragment of the protein was the unique active peptide, and its pharmacological profile was further studied.