Neurotensin and cholecystokinin contract gallbladder circular muscle in chickens.

The contractile effects of neurotensin (NT) and cholecystokinin octapeptide (CCK-8) on isolated circular smooth muscle strips of chicken gallbladder were investigated. The NT (0.25-300 nM) produced concentration-dependent contractions on smooth muscle with an EC50 of 8.5 nM (95% confidence limits = 5.3-13.6 nM). In comparison, CCK-8 produced concentration-dependent contractions with an EC50 of 13 nM (95% confidence limits of 9-20 nM). There were no statistical differences in contractile responses when comparing NT and CCK-8 at equimolar concentrations. The NT appears to act directly on smooth muscle tissue in the chicken; the contractile responses were not blocked by 10 µM atropine or tetrodotoxin. A portion of the activity is mediated by extracellular calcium as 100 nM nifedipine inhibited 30% of peptide-induced muscle tension. The NT receptor (NTR) type 1 antagonist SR 48692 (0.1 µM) did not significantly reduce NT potency. The contractile effects of CCK-8 remained unaltered in tissues pretreated with atropine, TTX, or nifedipine. The CCK-A antagonist lorglumide, at a concentration of 1 µM, reduced the contractile potency of CCK-8 by one-half. Avian receptors for NT and CCK may differ pharmacologically from their mammalian counterparts, but their contractile actions on the gallbladder resulting in increased biliary output by flow are further evidence of their role in the postprandial regulation of lipid digestion in chickens.

Neurotensin elevates hepatic bile acid secretion in chickens by a mechanism requiring an intact enterohepatic circulation.

Neurotensin (NT), given intravenously at 10-50 pmol/kg per min to anesthetized female chickens equipped with a bile duct fistula, dose-dependently elevated hepatic bile flow and bile acid output but only when the enterohepatic circulation was maintained by returning the bile to the intestinal lumen. Infusion of NT at 10 and 50 pmol/kg per min increased the average hepatic bile acid output over a 30-min period to 138 +/- 11 and 188 +/- 13% of control, respectively. During infusion of NT, plasma levels of immunoreactive NT (iNT) increased in time from the basal level (14 +/- 1.3 pM) to reach steady state at 30 min. There was a near linear relationship between the dose of NT infused and the increment in plasma iNT. In addition, infusion of NT at 40 pmol/kg min gave a plasma level of iNT (approximately/= 88 pM) which was within the range of those observed during duodenal perfusion with lipid (54-300 pM) and near to that measured in hepatic portal blood from fed animals (52 +/- 5 pM). Perfusion of duodenum with lipid released endogenous NT and increased the rate of hepatic bile flow. When NT antagonist SR48692 was given, bile flow rate decreased to the basal level. These results suggest that intestinal NT, released by lipid, may participate in the regulation of hepatic bile acid output by a mechanism requiring an intact enterohepatic circulation.

Effect of selective gastric intrinsic denervation on gastric motility in turkeys.

The effect of selectively denervating portions of the myenteric plexus on gastroduodenal (GD) motility was examined in domestic turkeys (Meleagris gallopavo). The neural network beneath the lateral or medial side of the isthmus between the glandular stomach and the muscular stomach was denervated by application of 1% benzalkonium chloride (BC). Image intensification radiology (IIR) was performed postsurgically on the research subjects to observe GD contractions and to analyze aberrations. Two trials were performed. The first employed temporal controls by checking GD motility in all treated birds before and after BC had taken effect. The second trial controlled for the trauma associated with the surgical procedure by applying 0.9% saline solution in lieu of BC in four turkeys. The normal GD contractions sequence as confirmed by these controls was thin muscle contraction, duodenal contraction and outflow, thick muscle contraction, and, finally, glandular stomach contraction. Ablation of the nerves beneath the medial or lateral side of the isthmus resulted in the same abnormality in GD motility, namely a lack of thick muscle contractions. These results indicate that the entire myenteric plexus associated with the isthmus must remain intact for proper GD motility to take place. Furthermore, it can be inferred that initiation and regulation of the thick muscle pair acts via nerves encircling the isthmus. Secondary regulatory mechanisms controlling GD motility may exist and should be tested through future investigation.

Identification of interstitial cells of Cajal in the digestive tract of turkeys (Meleagris gallopavo).

Interstitial cells of Cajal (ICCs) were identified in the digestive tract of turkeys by electron microscopy. ICCs have been implicated as sources of pacemaking slow wave potentials that initiate peristalsis in the stomach and intestines in mammals. The gastroduodenal contraction cycle in turkeys, however, is uniquely coordinated by a neurogenic pacemaker in the isthmus area between the glandular stomach and the gizzard, and this controls the coordinated phasic contractions of the muscles of the gizzard, duodenum and glandular stomach. Thus, it becomes important to look for the presence and distribution of ICCs in the avian digestive tract, especially in the gizzard and duodenum. This investigation has identified that cells are present which contain the typical characteristics of ICCs including: numerous mitochondria, caveolae, thin processes, basement membrane, filaments, rough ER, Golgi, and occasional gap junctions. They were mostly located in the region of the myenteric plexus between the longitudinal and circular muscle layers and occasionally within the longitudinal muscle layer. They were frequently near nerve axon bundles and were usually surrounded by collagen, elastin fibers, and occasional fibroblasts or blood vessels. ICCs were easily found in the ileum, but were also present in the duodenum, cecum, and rectum. None were found in the serosal region of the thick muscle of the gizzard. The presence of ICCs in the turkey duodenum, which like the gizzard is under neurogenic control, suggests that ICCs may play a role(s) in addition to initiating peristalsis.

Neurotensin modulates the composition of pancreatic exocrine secretions in chickens.

The effects of neurotensin on pancreatic exocrine secretion were examined in fasted, conscious White Leghorn hens. A cannula was surgically implanted in the central duct serving the ventral lobe of the pancreas in order to collect pure pancreatic juice. Following recovery, neurotensin was infused intravenously at 3.6 or 10.8 pmol/kg*min. The volume and pH of the pancreatic secretions were recorded and total pancreatic protein concentration, amylase, lipase, trypsin, and chymotrypsin activity were measured every 30 min for 2 hr and compared to secretions following the infusion of 0.9% saline. Our results demonstrated that neurotensin did not affect the pH nor the pancreatic juice protein concentration, but did increase secretion rate following neurotensin infusion at 3.6 pmol/kg*min. Amylase activity was significantly depressed during neurotensin infusions, while lipase (both pancreatic and carboxylester lipase) activity was significantly elevated. The ratio of amylase to lipase activity was especially depressed by neurotensin infusion at 10.8 pmol/kg*min. Insufficient secretory activity prevented a balanced statistical analysis of chymotrypsin activity, but from a pooled analysis, neurotensin had no effect on protease activity in the pancreatic juice. These results support our current research indicating that neurotensin may be a hormonal regulator of postprandial lipid digestion in chickens.

Effect of galanin on isolated strips of smooth muscle from the gastrointestinal tract of chickens.

The contractile effects of galanin on isolated longitudinal smooth muscle strips of pre-crop esophagus, proventriculus, duodenum, colon, and cecum of chickens were investigated. Application of galanin (5.0-100.0 nM) evoked strong contractions from the colon and cecum (hindgut), but evoked minimal responses from the pre-crop esophagus, proventriculus, and duodenum (foregut). Previous studies have demonstrated that the central administration of galanin stimulates food consumption in rats. Since galanin-like immunoreactivity is present in the chicken brain, we speculate that the central release of galanin may increase food intake and possibly be involved in a hypothalamic-colonic reflex modulating hindgut motility and generating a defecation. Thus, the results of this study demonstrate the presence of galanin receptors in the chicken gut and suggest a possible link with their functional presence in the hindgut to the chicken central nervous system.

Effect of fasting on small intestinal antiperistalsis in the Nicholas turkey (Meleagris gallopavo).

Small intestinal refluxes (SIRs) were monitored in the gastrointestinal tract of Nicholas turkeys via implanted strain gage transducers and radiographic observations. It was determined that reflux of ingesta from the small intestine into the gizzard was a result of a single antiperistaltic contraction. Radiographic observation indicated that the antiperistaltic contraction originated in the ileum 88% of the time and the duodenum 12% of the time. Each antiperistaltic contraction was preceded by a single peristaltic contraction. No gastric contractions occurred during SIRs. Fasting for 12 to 24 hr significantly increased the frequency of occurrence of SIRs in the Nicholas turkey (P < 0.0001) but had no significant effect on the velocity of the peristaltic and antiperistaltic contractions or on recovery time to pre-SIR gastric contractile frequency. The pooled mean velocity of peristaltic contractions was determined to be 10.55 +/- 3.68 cm/sec, and that of antiperistaltic contractions was determined to be 12.12 +/- 3.69 cm/sec. The pooled mean recovery time to pre-SIR gastric contraction frequency was 28.31 +/- 8.25 sec. It has been suggested that the SIR may be a mechanism of maximizing nutrient utilization by the turkey.

Mechanisms of excreta formation and elimination in turkeys and ostriches.

Undigested feed and precipitated uric acid are excreted together in domestic turkeys, whereas in ostriches, liquid urine then discrete fecal boli are excreted in rapid succession. Gross anatomy and physiology of the cloacal structures of these two species also differ, providing an explanation for the differences in their waste products.

Neurotensin decreases pepsin output and gastrointestinal motility in chickens.

Two experiments were conducted to determine the effect of neurotensin on gastric secretion and gastrointestinal motility in conscious chickens. Chickens were surgically fitted with a cannula to collect secretions from the proventriculus and strain gauge transducers sutured to the gizzard, duodenum, and ileum in order to detect contractions. Peripheral intravenous infusion of physiological levels of neurotensin inhibited pepsin output from the proventriculus, but had no effect on the volume or pH of gastric secretions. Neurotensin also inhibited both the frequency and strength of gastrointestinal contractions when compared to motility patterns following infusion of isotonic 0.9% (wt/vol) saline. The frequency of occurrence of small intestinal refluxes was not affected by neurotensin. These results coupled with our earlier work, which demonstrated that neurotensin is released by the presence of oleic acid in the duodenum, indicate that neurotensin may function as an enterogastrone released by lipids in the gastrointestinal tract of the chicken. This overall inhibitory effect of neurotensin on the avian gut indicates that it is involved in the postprandial regulation of digestion, especially lipid digestion.

Optimum duration of feed and water removal prior to processing in order to reduce the potential for fecal contamination in turkeys.

Feed and water withdrawal (FWW) prior to processing of poultry is an efficient and commonly employed method to attempt to reduce contamination of carcasses by contents of the gastrointestinal tract during processing. This study indicated that 4 h of FWW is as good as 8 or 12 h in reducing both water and dry matter content of the tract of market age turkeys of both sexes. This duration of FWW also minimizes shrinkage of the carcass.

Effects of dietary protein, methionine and lysine on urinary amino acid excretion in turkeys.

1. Two experiments were conducted to determine the influence of dietary protein and amino acids on urinary excretion of amino acids and nitrogen in colostomised turkey hens. 2. Normal and colostomised turkeys 8 weeks of age were fed on control and high protein diets. Body weight gains of both types of birds were similar. Diet did not affect the amino acids in the urine significantly, but urinary nitrogen was higher with the high protein diet. 3. Normal and colostomised turkeys 10 weeks of age were fed a diet with either supplemental DL-methionine or L-lysine hydrochloride (each 20 g/kg diet). DL-methionine depressed gain and resulted in considerable excretion of methionine in urine. Lysine had little effect on weight gain or urinary lysine.

An improved colostomy technique in turkeys.

1. A modified method for colostomy of turkeys was developed which allowed normal and consistent gains for 4 to 8 weeks. 2. Female Nicholas turkeys, 5 to 7 weeks of age and weighing 1.2 to 2.2 kg body weight, were subjects. Major adjustments in the technique included: transfixing of the peritoneum with 4 stay sutures prior to opening, suturing the peritoneum to the seromuscular coat of the colon, eversion of the end of the colon and joining of adjacent skin to the rim of the colon. 3. Urine was collected in a plastic bag attached around the vent with a urine collection fitting. Faeces passing through the colostomy were collected on a tray below the cage.

Effects of cecal ligation and colostomy on motility of the rectum, ileum, and cecum in turkeys.

Motilities of the rectum, ileum, and ceca were examined in surgically prepared turkeys by using strain gauge transducers implanted on these sites after cecal ligation or colostomy. All birds were provided ad libitum access to feed and water throughout the study. Cecal ligation increased the frequency of small anti-peristaltic contractions in the proximal (P < .01) and distal (P < .05) rectum and the frequency of defecations (P < .05) compared with intact controls. Cecal ligation decreased the frequency of single contractions in the proximal ileum (P < .05) and that of all contractions in the distal ileum (P < .05), and ligation (P < .01) and colostomy (P < .05) increased the frequency of single contractions in the distal site. However, major and minor cecal contractions were not affected by colostomy in the proximal and distal cecum. The results suggest that the effects on contractile activities of the hindgut must be considered when interpreting responses to cecal ligation and colostomy.

Intestine fullness influences feeding behaviour and crop filling in the domestic turkey.

Image-intensification radiology showed that artificial introduction of food slurry into the intestines of 6-12 wk-old turkey hens significantly increased the proportion of boli entering the crop during an evening meal, hence decreasing the proportion of boli travelling directly to the gizzard. Since bolus movement is directed by esophageal motility, esophageal motility may be partially mediated by stretch or chemoreceptors in the distal duodenum. Increased crop filling during afternoon meals lends support to the widely held belief that the crop increases gut storage capacity and helps "tide birds over" the nightly fast. Artificial filling of the distal duodenum paradoxically increased food intake in birds observed by radiology while eating a single meal (morning and evening), and in birds observed by eye over a 3 h period in the morning. This phenomenon is similar to that previously reported for rabbits and domestic chicken. Conversely, duodenal filing reduced food intake over a full day (11 h), more than compensating for the introduced food. Rapid filling of the small intestine (within 25 min. of the start of the meal) suggests a modification of the function of the domestic turkey duodenum to serve as a "mixing chamber," possibly enhancing digestive efficiency. The ways in which this modification affects digestion and absorption in the duodenum warrant investigation.

A common precursor to neurotensin and LANT6 and its differential processing in chicken tissues.

Antisera towards neurotensin (NT) and the structurally related peptide, LANT6, were used to characterize immunoreactive peptides and proteins in extracts of chicken tissues. A 17 kDa protein was identified by Western blotting as a potential precursor to NT and LANT6. However, the posttranslational processing of this common precursor appeared to be tissue specific, giving rise to disproportionate amounts of NT and LANT6, along with varying expression of a large molecular LANT6 (M(r), 15 kDa). The intestinal cells containing immunoreactive NT, LANT6, and large molecular LANT6 behaved similarly during fractionation by size and density. These activities also banded together in particles resembling vesicles during centrifugation of isotonic homogenates of tissue. These results suggest that chicken NT and LANT6 are biosynthesized as parts of the same precursor, the processing of which can give rise to a variety of products stored within secretory vesicles.

Research note: cardiovascular effects of neurotensin in anesthetized White Leghorn hens.

Solutions of neurotensin (NT) at 0, 12, 60, 120, and 600 nM were infused i.v. into anesthetized, 16- to 34-wk-old hens at 60 microL/kg per minute for 30 min. These infusates increased plasma NT concentrations to steady state values of about .1, .2, 1, 2, and 10 times the postprandial concentrations of NT in hepatic portal blood, respectively. None of these concentrations significantly affected heart rate or arterial (carotid) or central venous (jugular) blood pressure.

The effectiveness of ligating or detaching ceca as an alternative to cecectomy.

Cecectomy (the surgical removal of ceca) is a technique that has been used to explore the nutritional and osmoregulatory role of the ceca in domestic fowl and other birds. The operation imposes a high level of physiological stress on a bird. The current study describes the effectiveness of ligating or detaching the ceca in young turkeys as an alternative to complete removal of the organ. Birds with ligated ceca showed less postsurgical depression and initiated feeding and other normal activities sooner than birds with detached ceca. Birds with detached ceca also had a significantly slower rate of weight gain 1 wk after surgery. Both surgically treated groups were more depressed than were sham-operated turkeys. Post-mortem examinations revealed that cecal detachment was more successful in actually separating the ceca from the rectum and in preventing flow of digesta in and out of the ceca. Evidence of growth of cecal stumps that remained attached to the rectum was found following both ligation and detachment. Post-mortem examinations revealed that in four birds both ligated or detached ceca left in the abdominal cavity became enlarged and filled with a dark, pasty, odorous substance. This increase in cecal size and volume of contents with time apparently indicates that some microbial metabolic activity continued in the cecal lumen. If so, this might have negative implications for studies that assume that such ceca are no longer functional.

The influence of the stomach on crop function and feeding behavior in domestic turkeys.

We tested the hypotheses that motility of the crop and muscular stomach are coordinated and that the stomach exerts primary control over crop filling and emptying in domestic turkeys. Simultaneous recordings of motility of the crop, esophagus, and stomach with implanted strain gauge transducers and visual observations of food passage using image intensification radiography revealed an inverse relationship between the frequency of stomach and crop contractions. Artificially filling the stomach of a fasted turkey with a food slurry prior to feeding did not increase crop filling during the first morning meal, but it did inhibit crop emptying in fasted turkeys by markedly reducing the number of crop contractions. Artificially filling the crop of fasted turkeys prior to the first morning meal did not decrease the amount of feeding activity or the total amount of food consumed during that meal. It is suggested that meal termination is associated with the degree of inhibition of esophageal peristalsis.

Recent studies on regulation of gastric motility in turkeys.

Recent studies have been aimed at determining how gastroduodenal contractions are initiated and at regulation of the stomach during the intestinal phase of gastric regulation. Intrinsic, myogenic, electrical slow waves, the principal regulators of motility in the mammalian gut, have not been found in the avian gut. Instead, contractions appear to be initiated by a neurogenic pacemaker located between the gastric isthmus and the pylorus. Pacemaker impulses travel over the myenteric plexus to the glandular stomach and the duodenum, and to the muscles of the muscular stomach to initiate contractions. Extrinsic innervation does not appear to be involved in this initiation. The role of two hormones, avian pancreatic polypeptide (aPP) and cholecystokinin (CCK), in regulation of gastric motility has been examined. Both hormones are released postprandially by the presence of ingesta in the upper small intestine and both depress gastroduodenal motility when administered to fowl. Thus, aPP and CCK slow gastric emptying to allow more time for intestinal digestion.