Effect of L364718 on interdigestive pancreatic exocrine secretion and gastroduodenal motility in conscious sheep

Neurotensin and xenin stimulates pancreatic exocrine secretion through the peripheral cholinergic nerves in conscious sheep

The present study aimed to clarify the effects of neurotensin and xenin on pancreatic exocrine secretion in conscious sheep and their mechanism of actions. The animals were equipped with two silastic cannulae in the common bile duct to separately collect pancreatic fluid and bile, and a silastic cannula in the proximal duodenum to continuously return the mixed fluids. NT and xenin were intravenously injected at range of 0.01-3.0 nmol/kg during the phase I of duodenal migrating motor complex. A single intravenous NT injection significantly and dose-dependently increased pancreatic fluid, protein, and bicarbonate outputs. The effect of NT at 1 nmol/kg was completely inhibited by a background intravenous infusion of atropine methyl nitrate at a dose of 10 nmol/kg/min, however, the effect was not altered by a prior injection of the neurotensin receptor subtype (NTR)-1 antagonist SR 48692 at 60 nmol/kg. Moreover, a single intravenous xenin-25 injection significantly and dose-dependently increased pancreatic fluid and protein output, whereas the effect of xenin-25 did not clearly show dose-dependence. The prior SR 48692 injection at 30 nmol/kg did not significantly alter the effects of xenin-25 at 0.3 nmol/kg, while the atropine infusion significantly inhibited the increase in fluid secretion. Under the atropine infusion, xenin-25 at 0.3 nmol/kg did not increase protein and bicarbonate outputs, whereas the inhibitory effect of the atropine was not significant compared to that of the single injection of xenin-25. A single intravenous injection of NTR-2 agonist levocabastine at 0.1-3 nmol/kg did not alter pancreatic exocrine secretion. These results suggest that both NT and xenin-25 effectively stimulates pancreatic exocrine secretion through the peripheral cholinergic system in sheep and that NTR-2 is not involved in the regulation of pancreatic exocrine secretion, however, we did not precisely determine the role of NTR-1 in the actions of both the peptides on pancreatic exocrine secretion.

Role of tachykinins and neurokinin receptor subtypes in the regulation of motility of the forestomach and abomasum in conscious sheep

The present study was planned to evaluate role of tachykinins (TKs) and neurokinin (NK) receptors in the regulation of gastric motility in sheep. We examined the effects of intravenous (i.v.) injection of neurokinin A (NKA) and substance P (SP) on motility of the rumen, omasum, and abomasum in conscious sheep and the effects of NK receptor blockade on the effect of TKs using NK-1 receptor antagonist L-732,138 and NK-2 receptor antagonist SR48968. Moreover, the effect of NK receptor blockade on omasal cyclic contractions was examined. Intravenous injection of NKA and SP induced tonic contraction of rumen, omasum, and abomasum, and the contractile effect of NKA was more potent than that of SP in all the gastric regions. Although the effect of SP was not inhibited by L-732,138, the effect of NKA was significantly inhibited by SR48968. However, single infusion of SR48968 and L-732,138 did not alter cyclic electromyographic activity and basal intraluminal pressure in the omasum. These results imply that NKA and NK-2 receptors play a primary role in non-cholinergic regulation of ovine gastric motility, though NK-2 and NK-1 receptors seem unlikely to be involved in the physiological regulation of omasal cyclic contractions.

Localization of CCK-1R in the omasum and role of CCK in the regulation of omasal contractions in sheep

The present study examined localization of cholecystokinin receptor (CCK-R) mRNA in the muscle layer of the ovine omasum and role of CCK-R type 1 (CCK-1R) in the regulation of muscle contraction of the omasum. We demonstrated that not only CCK-R type 2 (CCK-2R) mRNA but also CCK-1R mRNA is highly expressed in the muscle layer of the ovine omasum. Application of CCK-8 to muscle strips of the greater curvature of the ovine omasum at 1-100 nM induced tonic contraction in a concentration-dependent manner, and the contractile effect of CCK-8 was inhibited by both CCK-1R antagonist lorglumide (IC(50) 2.7 and 7.9 microM in the longitudinal and circular muscle, respectively) and CCK-2R antagonist PD135,158 (IC(50) 51.4 microM in the longitudinal muscle), indicating that not only CCK-2R but also CCK-1R is functionally expressed in the plasma membrane of smooth muscles in the omasum and mediates action of exogenous CCK. Contractile effect of intravenous infusion of CCK-8 (1-30 pmol/kg/min) on omasal contraction was also confirmed in the in vivo experiments using conscious sheep in the absence and presence of atropine infusion (14.4 nmol/kg/min), and showed that circulating CCK increases omasal electromyographic (EMG) activity at lower plasma concentration than that it inhibits ruminal contractions. Taking account of our previous results in the in vivo study using other CCK-1R antagonist, it is suggested that circulating CCK, even at normal range of plasma concentration, plays a physiological role as a regulator of omasal contractions in sheep and CCK-1R mediates the action of CCK.

Effect of intravenous infusion of proglumide on ruminal motility in conscious sheep (Ovis aries)

The effects of intravenous infusion of proglumide on regular ruminal contractions were examined in conscious sheep using doses that inhibit pancreatic exocrine secretion. After a control period of 20 min, proglumide was infused intravenously for 40 min at a dose of 15, 30 or 60 micromol/kg per min and venous blood was collected. The intravenous infusion of proglumide significantly increased the frequency of ruminal contractions at 15 micromol/kg per min without altering the amplitude, while it significantly decreased the frequency and amplitude of ruminal contractions at 30 and 60 micromol/kg per min in a dose-dependent manner. Proglumide did not increase contractile activity of the omasum, abomasum and duodenum or the plasma concentration of immunoreactive cholecystokinin (CCK). Application of proglumide at 1-30 mmol/L inhibited bethanechol-induced contraction in both longitudinal and circular muscle strips of the dorsal sac of the rumen. These results suggest that proglumide at a low dose acts indirectly on the rumen as a CCK receptor antagonist to increase the frequency of contractions, whereas at higher doses it inhibits cholinergic-induced contraction of the ruminal muscles or acts as an agonist to inhibit contractions in sheep. Hence, proglumide at high doses seems unsuitable for research or therapeutic use as a CCK receptor blockade in sheep.

Regional differences in the effects of various doses of cerulein upon the small-intestinal migrating motor complex in fasted and non-fasted sheep

There are no precise data concerning the effect of cerulein on the small-intestinal migrating motor complex (MMC) in sheep. Thus, the effort was directed towards the elucidation of the role of cerulein, a cholecystokinin (CCK) amphibian analogue, in the regulation of MMC cycle in conscious fasted and non-fasted sheep in various regions of the small intestine. In six sheep, equipped with bipolar electrodes in the entire small intestine and with one duodenal strain gauge force transducer in four of these animals, the continuous myoelectric and motor activity recordings were performed. During control period, two normal consecutive MMC cycles were recorded in fasted and non-fasted animals and then cerulein was slowly injected at the dose 1 (during 30 s), 10 (during 30 s or 60 s) or 100 ng/kg (during 30 s, 60 s or 120 s) or infused at the dose 0.5 or 1.5 ng/kg/min during 60 min. After cerulein administration at least two consecutive MMC cycles were also recorded. It was found that cerulein in moderate and higher doses injected in both fasted and non-fasted animals, especially during phase 2a or 2b MMC, inhibited phase 3 in the duodenum in at least one-third of the experiments and significantly increased the MMC cycle duration. The application of 100 ng/kg of cerulein during 120 s in the course of phase 2b MMC prolonged cycle duration from 70 +/- 21 to 113 +/- 19 min (p < 0.05) or from 51 +/- 18 to 113 +/- 19 min (p < 0.01) in fasted and non-fasted sheep respectively. The first phase 3 MMC arriving after cerulein administration at the highest dose was usually abnormal in approximately 60% of the experiments. The second phase 3 observed following the hormone injection was abnormal much less frequently and to the lesser extent. Furthermore, both cerulein doses significantly shortened the duration of phase 3 MMC either in fasted (from approximately 5.5-6.5 cpm to 4-5 cpm) or in non-fasted sheep (from approximately 4.5-5.5 to 3-4.5 cpm). The effects of cerulein exhibited the dose-response character. They were more pronounced when cerulein was injected during phase 2b or 2a MMC when compared with phase 1 MMC. The effects of cerulein on the ileal MMC were less evident, although the inhibition of the ileal phase 3 in response to both higher injected doses was observed occasionally. Infusions of cerulein in non-fasted sheep exerted similar effects as cerulein injections. It was stated that cerulein exerts marked regulatory effect upon the small-intestinal MMC in sheep. Although it remains uncertain whether the efficient doses of cerulein used in the present study correspond to physiological or pharmacological doses of CCK it seems likely that most of these doses were physiological. Thus, it is concluded that cerulein participates in the control of MMC cycles in the digestive and interdigestive states in sheep. It is possible that CCK is a physiological regulator of the ovine small-intestinal MMC.

Effects of nitric oxide donor and nitric oxide synthase inhibitor on ruminal contractions in conscious sheep

The present study was planned to evaluate a role of nitric oxide (NO) in the regulation of regular ruminal contractions in conscious sheep. Intravenous infusion of S-nitroso-acetyl-DL-penicillamine (SNAP) at doses of 3-30 nmol kg(-1) min(-1)for 30 minutes inhibited both the amplitude and frequency of ruminal contractions in a dose-dependent manner. However, intravenous infusion of Nomega-nitro-L-arginine-methyl ester (L-NAME) at doses of 0.3-3.0 micromol kg(-1) min(-1)did not alter the basal tone of intraruminal pressure and the amplitude of ruminal contractions. The frequency of contractions was slightly inhibited by L-NAME infusion at 1.0 micromol kg(-1)min(-1). The effects of L-NAME were abolished by simultaneous infusion of L -arginine at 30 micromol kg(-1) min(-1). These results suggest that exogenous NO can diminish the ruminal contractions, while endogenous NO is not involved in the regulatory mechanism of basal tone and regular phasic contractions of the rumen in healthy sheep.

Stimulation of rat pancreatic exocrine secretion by cocaine- and amphetamine-regulated transcript peptide

Cocaine- and amphetamine-regulated transcript (CART) peptide is a recently described neuropeptide that has been localized to areas of the central and peripheral nervous systems. CART has been shown to be involved in feeding behavior when injected centrally, however, its effects upon peripheral tissues have not been studied. This report describes the effects of CART peptide on rat pancreatic exocrine secretion. Infusion of CART peptide caused four-fold increases in amylase secretion from anesthetized rats that had been fashioned with a bile-pancreatic duct cannula. CART peptide-induced increases in pancreatic secretion appear to involve pathways that are sensitive to both acetylcholine (ACh) and cholecystokinin (CCK) since pre-treatment with atropine (ACh receptor antagonist) or L-364,718 (CCK-A receptor antagonist) inhibited the effects of CART peptide on amylase secretion. Pre-treatment with a combination of atropine and L-364,718 abolished the effects of CART peptide. When isolated rat pancreatic acini were exposed to varying doses of CART peptide, no increase in amylase secretion was observed. The results of the present study suggest that CART peptide has stimulatory effects upon pancreatic exocrine secretion. CART peptide-induced increases in pancreatic secretion appear to be indirectly mediated as no direct effect upon pancreatic acini was shown. CART peptide likely acts upon either peripheral or central regulators of pancreatic secretory function that are distant from the acinar unit.