Endothelin-1 induces itch and pain in the mouse cheek model.

AIMS: To date, suggestions that endothelin-1 (ET-1) causes nociception and pruritus are based on results in preclinical models in which responses to pruritic and nociceptive stimuli cannot be distinguished. This study reexamines these sensory effects of ET-1 in the new mouse cheek model, in which pruritogens and algogens evoke distinct behavioral responses. MAIN METHODS: Mice received intradermal (i.d.) injections of test substances into the left cheek and bouts of hind limb scratches or forepaw wipes, directed to the injection site, were considered indicative of pruritus and nociception, respectively. KEY FINDINGS: Histamine and capsaicin selectively evoked scratching and wipes, respectively, whereas ET-1 (3-60 pmol) promoted dose-dependent bouts of both behaviors. While scratching and wipe responses to ET-1 (30 pmol) were potentiated by BQ-788 (an ET(B) receptor antagonist) and reduced by co-injection of BQ-788 plus BQ-123 (an ET(A) receptor antagonist), BQ-123 alone inhibited scratching responses only. CTOP (µ-opioid receptor selective antagonist) only augmented scratching responses to ET-1, whereas DAMGO (µ-opioid receptor selective agonist) reduced both behaviors. Loratadine (histamine H(1) receptor antagonist) marginally reduced scratching, but markedly suppressed wipes. SIGNIFICANCE: These results demonstrate that ET-1 evokes pruritic and nociceptive behaviors in the mouse cheek model. Both responses to ET-1 appear to be mediated via ET(A) receptors and subjected to limitation by simultaneous ET(B) receptor activation. Local endogenous opioids acting on µ-opioid receptors selectively modulate the pruritic response to ET-1, whereas histamine, possibly derived from mast cells and acting on H(1) receptors, contributes importantly to the nociceptive effect of ET-1 in this model.

Mechanisms involved in the long-term modulation of tyrosine hydroxylase by endothelins in the olfactory bulb of normotensive rats.

The olfactory bulbs play a relevant role in the interaction between the animal and its environment. The existence of endothelin-1 and -3 in the rat olfactory bulbs suggests their role in the control of diverse functions regulated at this level. Tyrosine hydroxylase, a crucial enzyme in catecholamine biosynthesis, is tightly regulated by short- and long-term mechanisms. We have previously reported that in the olfactory bulbs endothelins participate in the short-term tyrosine hydroxylase regulation involving complex mechanisms. In the present work we studied the effect of long-term stimulation by endothelins on tyrosine hydroxylase in the rat olfactory bulbs. Our findings show that endothelin-1 and -3 modulated catecholaminergic transmission by increasing enzymatic activity. However, these peptides acted through different receptors and intracellular pathways. Endothelin-1 enhanced tyrosine hydroxylase activity through a super high affinity ET(A) receptor and cAMP/PKA and CaMK-II pathways, whereas, endothelin-3 through a super high affinity atypical receptor coupled to cAMP/PKA, PLC/PKC and CaMK-II pathways. Endothelins also increased tyrosine hydroxylase mRNA and the enzyme total level as well as the phosphorylation of Ser 19, 31 and 40 sites. Furthermore, both peptides stimulated dopamine turnover and reduced its endogenous content. These findings support that endothelins are involved in the long-term regulation of tyrosine hydroxylase, leading to an increase in the catecholaminergic activity which might be implicated in the development and/or maintenance of diverse pathologies involving the olfactory bulbs.

Pharmacologic and molecular characterization of the vascular ETA receptor in the venomous snake Bothrops jararaca.

Endothelins (ETs) and sarafotoxins (SRTXs) are active isopeptides that have very similar structures and functions. All isoforms interact with two specific G-protein-coupled receptors, ET(A) and ET(B). To characterize functional vascular ET receptors in the poisonous snake, Bothrops jararaca, cumulative concentration-response curves to ETs and SRTXs were performed in isolated aortic rings, in the absence and presence of selective ET receptor antagonists. Vascular expression of ET receptor messenger RNA (mRNA) was evaluated by reverse transcriptase (RT) polymerase chain reaction (PCR) analysis, and a fragment of the ET(A) receptor was cloned and sequenced. In vivo, ET-1 induced a dose-dependent biphasic response on anesthetized B. jararaca snakes. In vitro, ET-1, SRTX-b, ET-3, SRTX-c, and IRL-1620 induced concentration-dependent vasoconstriction, with a potency order suggesting the presence of typical ET(A) receptors. BQ-123, a selective ET(A) antagonist, inhibited contractions induced by ET-1 and SRTX-b with expected negative log of the dissociation constant, K(B), (pK(B)) values for mixed ET(A)/ET(B) receptor populations. The nonselective ET(A)/ET(B) receptors antagonist, PD-142893, produced similar inhibition. The ET(B) antagonist, IRL-1038, potentiated contractile responses to SRTX-c. ET-1 and SRTX-c responses were also potentiated when aortic rings were pretreated with N(omega)-nitro-L-arginine methyl ester (L-NAME) plus indomethacin. Processing of the B. jararaca aortic first-strand complementary DNA, by RT-PCR with primers designed from the Gallus gallus ET(A) receptor sequence, enabled isolation, purification, cloning, and sequencing of a single band. The partial sequence of the B. jararaca ET(A) receptor showed a very high sequence similarity with ET(A) receptor sequences from chicken, rat, human, and Xenopus. In conclusion, vascular responses to SRTXs/ETs in the B. jararaca aorta are mediated predominantly, but not exclusively, by typical ET(A) receptors.