Tsuyoshi Ozaki

Salivary Secretion of Highly Concentrated Chromogranin a in Response to Noradrenaline and Acetylcholine in Isolated and Perfused Rat Submandibular Glands

Chromogranin A (CgA) is a member of a family of highly acidic proteins, chromogranins, which are co‐stored in the adrenergic neurons and paraneurons and co‐released with adrenaline and noradrenaline (NAd) in response to adequate stimulation. The present study provides novel evidence that CgA‐like immunoreactivity (IR) is stored in the exocrine cells in the granular convoluted tubule, and is secreted into saliva by stimulation with NAd and acetylcholine (ACh) in the isolated and perfused rat submandibular gland. NAd at 1 μM produced maximum secretion of CgA‐like IR (<< 0.9 mM) and a marked increase in salivary flow. Further increases in NAd concentration (10 or 100 μM) yielded concentration‐dependent decreases in both responses. ACh at 1 μM produced maximum salivary flow and a slight elevation of CgA‐like IR secretion (6 μM); 100 μM ACh decreased the salivary flow but increased the CgA‐like IR secretion (0.6 mM). Electron microscopic examination showed vigorous compound exocytosis of secretory granules in the cells of the granular convoluted tubule when the submandibular gland was stimulated with 1 μM NAd. These results provide an experimental basis for the view that the salivary CgA‐like IR secretion may be a sensitive and quantitative index of the activity of the sympathetic nervous system innervating the gland.

Galanin suppresses neurally evoked contractions of circular muscle in the guinea-pig ileum

The effect of galanin, a 29 amino-acid peptide, on intestinal smooth muscles was studied in guinea-pig ileum. Galanin did not affect the basal activity of longitudinal or circular muscles. Galanin decreased neurally evoked circular muscle contractions in a dose-dependent manner, but failed to affect neurally evoked longitudinal muscle contractions. Galanin also decreased neurally evoked circular muscle contractions in the presence of atropine. The neurally evoked phasic contractions were blocked by TTX. These findings indicate that galanin has an inhibitory role in circular muscle contractions via myenteric neurons in the guinea-pig ileum.

Structural requirements for galanin action in the guinea-pig ileum

Galanin fragments and galanin analogues were tested on neurally evoked muscle contractions in guinea-pig ileum in vitro. Galanin fragments inhibited the neurally evoked circular muscle contractions with the following order of potency: Galanin(1-29), galanin(2-29), galanin(1-15). In contrast, galanin(3-29), galanin(10-29), galanin(21-29), [D-Trp2]galanin, [Phe2]galanin and [Tyr2]galanin were ineffective. Galanin(1-29), galanin(2-29) and galanin(1-15) did not affect the neurally evoked longitudinal muscle contractions. These results indicate that (1) the two N-terminal amino acid residues of the galanin molecule are essential for the inhibitory action of galanin on neurally-evoked circular muscle contraction and (2) for the full potency also the C-terminal end is required.

Calcitonin gene-related peptide is a potent intestinal, but not gastric, vasodilator in conscious dogs

The effects of human alpha-calcitonin gene-related peptide (alpha-CGRP), beta-CGRP, and vasoactive intestinal polypeptide (VIP) on left gastric (LGA) and superior mesenteric arterial (SMA) blood flow, heart rate and systemic arterial blood pressure were investigated in 6 conscious beagle dogs. Both intravenous injections of alpha-CGRP and beta-CGRP (5-200 pmol/kg) and infusion of alpha-CGRP (25-100 pmol/kg per h) induced a dose-related increase in SMA flow and a dose-related decrease in its resistance. At lower doses, alpha-CGRP was more potent than beta-CGRP, but their maximal responses were the same. alpha-CGRP and beta-CGRP had little effect on LGA flow. However, alpha-CGRP at 200 pmol/kg, but not beta-CGRP, stimulated gastroduodenal contractions that were associated with a phasic increase of LGA flow. Atropine inhibited gastric, but not duodenal, motor and circulatory responses to alpha-CGRP. Tachycardia and hypotension induced by beta-CGRP were significantly less than those by alpha-CGRP. VIP, on the other hand, increased mainly LGA flow. These results suggest that blood vessels of the small intestine of dogs are more sensitive to CGRP than those of the stomach, while the sensitivity to VIP is reversed.

Role of peptide YY in regulation of duodenal motility during the interdigestive period in sheep

Abstract Temporal coordination between duodenal migrating myoelectric complexes (MMC) and pancreatic exocrine secretion, and the effects of porcine peptide YY (PYY) on gastroduodenal motility and pancreatic exocrine secretion were examined during the interdigestive period in conscious mature sheep. Fluid and enzyme secretions from the exocrine pancreas showed a periodic pattern corresponding to the phases of duodenal MMC, although these secretion rates were maintained at a high level during phase II in sheep. Intravenous continuous infusion of PYY at doses ranging from 50 to 200 pmol · kg−1 · h−1 or intravenous bolus infusion of PYY at doses ranging from 50 to 200 pmol · kg−1 showed a tendency to prolong the first cycle of the duodenal MMC and significantly shorten the second cycle. However, there was almost no effect on ruminal contractions from the PYY administration. In the pancreatic exocrine secretion, PYY could inhibit only bicarbonate secretion at only the highest dose of 200 pmol · kg−1. These results imply that endogenous PYY may play a physiological role in the regulation of the duodenal MMC cycles in sheep but not in ruminal contractions. PYY seems unlikely to regulate the pancreatic exocrine secretion in normal sheep, because a supraphysiological dose of PYY was required to inhibit the pancreatic exocrine secretion.

Effect of gastrin-releasing peptide (GRP) on guinea pig gallbladder contrction in vitro

Few studies have reported the effects of gastrin-releasing peptide (GRP)/bombesin on the guineas pig gallbladder, and the results are contradictory. Because such contradictory results may, in part, be due to technical factors, we investigated the effect of GRP on guinea pig gallbaladder smooth muscle, using a improved horizontal organ bath. The guinea pigs were killed and the gallbladder was removed. Four longitudinal uscle strips (2×12mm) were suspended in Krebs-Ringer solution at 37°C and aerated with 95% O2 and 5% CO2. The mechanical activity of the strips was recorded isotonically by displacement-voltage transducers. via L-arms, to which a piezoelectric element with a frequency of 100Hz and movement of 50μm was applied. GRP contracted gallbladder muscle strips dose dependently, but the calculated maximal response was 22.4% and 20.1% of the acetylcholine-and cholecystokinin octapeptide (CCK8)-induced responses, respectively. The GRP-induced contraction was unaffected by the muscarinic blocker, atropine, or by the CCK receptor antagonist, loxiglumide. It is concluded that GRP weakly, but apparently directly, stimulates guinea pig gallbladder contraction.

Sodium nitrite, a potent relaxant of rat stomach fundus: in vitro evidence

The effects of sodium nitrite (0.1, 1, 10 mM) on mechanical activity of isolated rat stomach fundus muscle and the influence of guanylate cyclase activity inhibitor (methylene blue) and channel inhibitors (tetrodotoxin, charybdotoxin, apamin) were studied. Nitrite evoked dose-dependent relaxation in the longitudinal and circular muscle layers. The lowest effective concentration of sodium nitrite was 0.1 mM, which is comparable with the NOAEL (no observed adverse effect level). Tetrodotoxin (1 microM) markedly inhibited electrically induced contraction and rebound relaxation, but did not influence the nitrite-induced relaxation. Charybdotoxin (100 nM) decreased the relaxation evoked by 10 mM nitrite to 52.3 and 65.7% of control reaction in the circular and longitudinal muscle layer, respectively. Apamin (100 nM) did not influence the nitrite-induced relaxation. Methylene blue (10 microM) decreased relaxation induced by nitrite in the longitudinal and circular muscle layer, respectively, to 66.7 and 54.3% of the response to 1 mM nitrite alone. Relaxation induced by nitrite was decreased in the presence of L-cysteine (5 mM), and in the circular and longitudinal muscle layer reached 29.6 and 23.1%, respectively, of the response to 1 mM nitrite alone. We conclude that the relaxing effect of nitrite on gastric fundus results from its direct action on smooth muscle cells and probably the enteric nervous system is not involved in this action. The nitrite-elicited relaxation depends on activation of guanylate cyclase and high conductance Ca2+-activated potassium channels; however, activation of potassium channels might be a part of or might act in parallel with the mechanism involving the cyclic GMP system. Effects of nitrite observed in the presence of L-cysteine suggest that nitrosothiols are not responsible for nitrite-evoked activation of guanylate cyclase.