Neurokinin A-stimulated phosphoinositide breakdown in rabbit iris sphincter muscle

Peptidergic nerves in the eye, their source and potential pathophysiological relevance

Over the last five decades, several neuropeptides have been discovered which subsequently have been found to be highly conserved during evolution, to be widely distributed both in the central and peripheral nervous system and which act as neurotransmitters and/or neuromodulators. In the eye, the first peptide to be explored was substance P which was reported to be present in the retina but also in peripherally innervated tissues of the eye. Substance P is certainly the best characterized peptide which has been found in sensory neurons innervating the eye. Functionally, it has been shown to act trophically on corneal wound healing and to participate in the irritative response in lower mammals, a model for neurogenic inflammation, where it mediates the noncholinergic nonadrenergic contraction of the sphincter muscle. Over the last three decades, the interest has extended to investigate the presence and distribution of other neuropeptides including calcitonin gene-related peptide, vasoactive intestinal polypeptide, neuropeptide Y, pituitary adenylate cyclase-activating polypeptides, cholecystokinin, somatostatin, neuronal nitric oxide, galanin, neurokinin A or secretoneurin and important functional results have been obtained for these peptides. This review focuses on summarizing the current knowledge about neuropeptides in the eye excluding the retina and retinal pigment epithelium and to elucidate their potential functional significance.

Tachykinin receptors in the spinal cord

In summary, all three tachykinin receptors appear to be important modulators of physiological systems in the spinal cord. However, although there is a good deal of data concerning binding characteristics in peripheral tissues, work done in the spinal cord is scanty, leading to a number of unanswered questions. Firstly, Lui et al. (1993) have suggested a discrepancy between the location of SP binding sites and SP containing terminals. This might explain the conflicting evidence on the role of NK1 receptors in the dorsal horn. Furthermore, evidence that NK2 receptors are involved in nociception is increasing, however binding sites for these receptors in the spinal cord have not been demonstrated. This appears to be due to the difficulty in locating an ideal receptor specific ligand. The role of NK2 receptors in autonomic function is also unclear, perhaps for the same reason. Finally, there is evidence indicating that NK3 binding sites are increased following transection of the LIV-VI dorsal roots, however, studies on the effects of inflammation have not been done, as they have with the NK1 and NK2 receptors. All of these and many more unanswered questions require further investigation.

Interactions between inhibitory and excitatory modulatory signals in single submucosal neurons

Intracellular recordings were made in submucosal neurons from the guinea pig ileum to study the actions of norepinephrine and somatostatin on slow depolarizations induced by 2-chloroadenosine (CADO) and substance P. Local application (by pressure) of CADO and substance P induced a slow depolarization that occurred concomitantly with an increase in input membrane resistance. Norepinephrine, UK-14304 (alpha 2-adrenoceptor agonist), and somatostatin blocked the excitatory responses induced by CADO in a concentration-dependent manner. The alpha 2-adrenoceptor antagonists idazoxan and yohimbine antagonized these inhibitory effects of UK-14304 and norepinephrine. UK-14304 also decreased depolarizations induced by forskolin, but not those induced by the adenosine 3',5'-cyclic monophosphate analogue 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate. Slow depolarizations induced by substance P were blocked neither by UK-14304 nor by somatostatin. It was previously shown that staurosporine (an inhibitor of various protein kinases) and KT-5720 (an inhibitor of protein kinase A) inhibited slow depolarizations induced by CADO. Here, substance P depolarizations were inhibited by staurosporine and calphostin C (a blocker of protein kinase C) but not by KT-5720. In conclusion, activation of alpha 2-adrenoceptors and somatostatin receptors selectively blocks excitatory responses induced by CADO, most likely by inhibition of adenylyl cyclase and via pertussis toxin-sensitive G proteins. Slow depolarizations induced by substance P are independent of adenylyl cyclase activation and involve activation of protein kinase C.

Biochemical and pharmacological properties of a newly synthesized proton pump (H+/K(+)-ATPase) inhibitor, TY-11345 in experimental animals

We investigated the effects of the newly synthesized proton pump inhibitor TY-11345, (+/-)-2-[(4-methoxy-6,7,8,9-tetrahydro-5H-cyclohepta[b]pyridin- 9-yl)sulfinyl]-1H-benzimidazole sodium salt, on gastric mucosal proton pump (H+/K(+)-ATPase) activity, gastric acid secretion and gastro-duodenal lesions in experimental animals. TY-11345 potently inhibited H+/K(+)-ATPase activity in isolated rabbit gastric mucosal microsomes; and the inhibitory effect was enhanced under weak acid conditions, the IC50 (concentrations that inhibit the enzyme activity by 50%) being 5.8 microM and 9.9 microM at pH 6.0 and pH 7.4, respectively. In Ghosh & Schild rats, intravenous injection of TY-11345 significantly inhibited gastric acid secretion stimulated by tetragastrin; the effect of TY-11345 was twice as potent as that of omeprazole. In pylorus ligated rats, TY-11345 inhibited basal gastric acid secretion by both the intraduodenal and oral routes, with ED50 values of 1.2 and 4.0 mg/kg, respectively. These effects were 9 and 5 times more potent than those of omeprazole, respectively. Moreover, the antisecretory effect of TY-11345 persisted for more than 24 hr in pylorus ligated rats. In experimental ulcer models, TY-11345 prevented the formation of water-immersion stress, ethanol or indomethacin-induced gastric lesions and mepirizole-induced duodenal lesions in rats. The antiulcer effects of TY-11345 were 3 to 15 times more potent than those of omeprazole. These results suggest that TY-11345 has potent antisecretory and antiulcer effects which are exerted by suppression of H+/K(+)-ATPase activity in gastric parietal cells, so that TY-11345 should be useful for the clinical treatment of peptic ulcer diseases.