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The 17-amino acid peptide nociceptin/orphanin FQ (N/OFQ) plays a role in the regulation of stress responses and of emotional disorders. The objective of this study is to evaluate whether long-term peripheral N/OFQ could dose- and time-dependently influence the responses to repeated cold-restraint stress on the rat gastric and colonic mucosa. Rats were exposed to cold-restraint stress for 3h per day for 1, 2 and 3 consecutive days. N/OFQ was administered at doses of 0.1, 1 and 10 microg/kg/h via Alzet osmotic minipumps. In the gastric fundus, N/OFQ exerted dose-dependent beneficial effects against acute and repeated stress but, after prolonged treatment, became damaging in non-stressed rats. In the distal colon, N/OFQ exerted a protective effect against damage by acute and repeated stress with no influence on epithelial integrity in non-stressed rats. In both regions, the peptide itself dose- and time-dependently reduced intraepithelial mucins. The reduction in mucin content caused by stress was effectively counteracted by N/OFQ, 0.1 microg/kg/h, in the distal colon only. N/OFQ did not modify basal mucosal cell proliferation. The peptide at 0.1 and 1 microg/kg/h had no influence while at 10 microg/kg/h abolished stress-induced increase in cell proliferation. The present results provide evidence that N/OFQ is implicated in the regulation of resting and stress-challenged mucosal integrity and activity of mucin-producing cells.

This study investigated the sensitivity of spontaneously hypertensive rats (SHR) and of Wistar Kyoto rats (WKR) to the antidipsogenic action of the tachykinin eledoisin (ELE). Drinking was evoked by: (a) intracerebroventricular (i.c.v.) injection of angiotensin II, (b) subcutaneous (s.c.) administration of hypertonic NaCl (1.5 M; 1 ml/100 g b.wt.) or (c) 18 h of water deprivation with free access to food. In accordance with previous studies, the dipsogenic effect of all three treatments was exaggerated in the SHR. And when treated with i.c.v. ELE (12.5–25 ng/rat) they were far less sensitive than WKR to its antidipsogenic action on angiotensin-induced drinking. Smaller differences in strain sensitivity were also observed for the effect of ELE on cell dehydration- and on water deprivation-induced drinking, but only at the dose of 200 and 50 ng/rat, respectively. The different sensitivity of the SHR to the antidipsogenic effect of ELE supports the idea that tachykininergic mechanisms for control of water intake are differently regulated in the SHR than they are in the normotensive WKR.

Nociceptin/orphanin FQ (N/OFQ), the endogenous ligand of the NOP receptor, exerts a variety of effects on the gastrointestinal tract. The present study was aimed at evaluating the possible implication of N/OFQ in the maintenance of gastric mucosal integrity. N/OFQ was given either centrally or peripherally 30 min prior to intragastric administration (i.g.) of 1 ml/rat of ethanol (either 25% or 50%, v/v), which produces macroscopically visible gastric lesions. Intracerebroventricular (i.c.v.) injection of 2 microg/rat of N/OFQ significantly reduced lesions caused by 50% ethanol, while 1 microg/rat was enough to significantly reduce lesions caused by 25% ethanol. Intracerebroventricular injection of 5 microg/rat of the selective NOP receptor antagonist, UFP-101, completely reversed the protective effect of N/OFQ, 1 or 4 microg/rat against 25% or 50% ethanol, respectively. The intraperitoneal (i.p.) injection of N/OFQ produced a significant reduction of lesions induced by 50% ethanol, the peak effect being observed at 10 microg/kg. Intraperitoneal pretreatment with UFP-101, 120 microg/kg, completely abolished the protective effect of peripherally injected N/OFQ. Therefore, N/OFQ acts both centrally and peripherally as a protective agent against ethanol-induced gastric lesions, and its effect is mediated by NOP receptors.

Our previous studies have shown that i.c.v. injections of the selective tachykinin NK3 receptor agonist [Asp5,6,MePhe8]substance P(5,11), also referred to as NH2-senktide (NH2-SENK), inhibit salt intake in rats in a two-bottle intake test. The present study evaluated the effect of i.c.v. injections of NH2-SENK on intraoral intake and taste reactivity responses elicited by intraoral infusions of water or NaCl solutions (0.03, 0.15, 0.25 and 0.5 M) in sodium-replete rats. The effect of NH2-SENK on the intake of 0.03, 0.15 and 0.25 M NaCl solutions and of water was also evaluated in a two-bottle intake test. In this test, 31 ng/rat of NH2-SENK significantly reduced the intake of 0.15 and 0.25 M NaCl, but not that of water or of 0.03 M NaCl. The dose of 31 ng/rat of NH2-SENK reduced the intraoral intake of 0.25 and 0.5 M NaCl, while 125 ng/rat reduced the intraoral intake of 0.15, 0.25 and 0.5 M NaCl; neither dose reduced the intraoral intake of water or of 0.03 M NaCl. Taken together, these findings indicate that the effect of NH2-SENK on salt intake is dependent on the concentration of the NaCl solution offered; moreover, the intraoral intake data suggest that the effect of NH2-SENK on salt intake may be exerted to a large extent on the consummatory processes of salt ingestion. NH2-SENK, 31 or 125 ng/rat, altered taste reactivity responses shortly after the beginning of the intraoral infusion. The most peculiar effect was an increase in passive dripping during the first min of intraoral infusion of 0.15, 0.25 and 0.5 M, but not of water or of 0.03 M NaCl. This finding suggests that NH2-SENK elicits a prompt alteration of taste mechanisms for salt, which may account for its antinatriorexic action.

Intracerebroventricular (i.c.v.) injection of kassinin produced a prompt and copious drinking response at doses of 10-1000 ng/pigeon, in the absence of other behavioural alterations or of changes in core temperature. Neurokinin A and B evoked drinking, but they were respectively 10 and 100 times less potent than kassinin. Intraperitoneal injection of kassinin elicited drinking, but at doses about 1000 X larger than the i.c.v. ones. The angiotensin antagonist [Sar1, Leu8]angiotensin II did not reduce drinking induced by i.c.v. kassinin, suggesting that its effect is not due to interaction with the central renin-angiotensin system. Moreover, the effect is apparently independent of the mechanisms controlling hypovolaemic and hyperosmotic thirst since exact additivity was found in the dipsogenic response when i.c.v. kassinin was administered in the presence of a hypovolaemic (subcutaneous (s.c.), polyethylene glycol) or hyperosmotic (s.c. hypertonic NaCl) dipsogenic stimulus. The present findings show that kassinin, neurokinin A and B share with the tachykinins already tested (eledoisin, physalaemin, substance P) a common dipsogenic action in pigeons. However, marked differences exist in their dipsogenic potency. This order of potency, eledoisin = kassinin = physalaemin greater than neurokinin A = substance P greater than neurokinin B, is not consistent with the tachykinin receptor subtypes so far proposed.

The present study investigates the effect of the mammalian tachykinin neurokinin A on salt intake in the rat. Intracerebroventricular injection of neurokinin A inhibited salt intake elicited by sodium depletion, by subchronic deoxycorticosterone treatment and by adrenalectomy. It also inhibited the need-free salt intake of female rats that had been previously depleted of sodium. Since different brain mechanisms elicit salt intake in these experimental models, it is concluded that neurokinin A exerts a general antinatriorexic effect. Apparently, its inhibitory effect on salt intake is not due to malaise or competing behaviors, as shown by the fact that the doses of neurokinin A which suppress salt intake do not suppress milk intake. In comparison to the amphibian tachykinin kassinin, neurokinin A possesses a similar spectrum of antinatriorexic activities, but is markedly less potent and less effective in all the experimental models investigated. These findings suggest that activation of neurokinin A receptors cannot solely account for the potent antinatriorexic effect of kassinin and of other non-mammalian tachykinins.