cDNA cloning of ghrelin and ontogeny of ghrelin mRNA expression in the gastrointestinal tract of African ostrich chicks.

Ghrelin is the endogenous ligand for the growth hormone secretagogue receptor (GHS-R). The sequence of ghrelin has been determined in many species ranging from fish to mammals. The ostrich is the largest herbivorous bird in the world. Although the distribution, morphological characteristics, and developmental changes of ghrelin-producing cells in the gastrointestinal tract of African ostrich chicks have recently been determined, the sequence and structure of ghrelin and its expression in the gastrointestinal tract of African ostrich chicks have not been studied. In the present study, the sequence and structure of ghrelin and its expression in the gastrointestinal tract of African ostrich chicks were investigated by reverse-transcriptase polymerase chain reaction (RT-PCR). Results of cDNA cloning revealed that African ostrich ghrelin is composed of 28 amino acid residues and the sequence of the 7 amino acids of the N-terminal region of African ostrich ghrelin was identical with that of other birds. Ninety-day-old female African ostriches were used to investigate the expression of ghrelin in the gastrointestinal tract. The results showed that ghrelin mRNA existed in the proventriculus, gizzard, duodenum, ileum, cecum, and rectum; there was no expression in the jejunum and colon. We observed developmental changes in the ghrelin mRNA expression in the stomach and small intestine of African ostriches. The results of the present study showed that ghrelin mRNA existed on day 1 in the proventriculus, but there was no expression in other tissues. On day 45, ghrelin mRNA existed in the proventriculus, gizzard, and ileum; however, there was no expression in the duodenum and jejunum. On day 90 and 334, we detected ghrelin mRNA in the proventriculus, gizzard, duodenum, and ileum, but there was no expression in the jejunum. The results of the present study clearly demonstrate that ghrelin mRNA exists and the distribution of ghrelin mRNA in the gastrointestinal tract of African ostriches changes with age (from postnatal day 1 to day 334).

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.

Release of avian pancreatic polypeptide by various intraluminal contents in the stomach, duodenum, or ileum of turkeys.

Pancreatic polypeptide (PP) has been shown to be released postprandially in several species. In this study we tested the efficacy of an amino acid solution (905 mOsM), 0.1 N HCl (300 mOsM), 905 mOsM NaCl, 300 mOsM glucose, corn oil, and balloon distention within the stomach, duodenum, or ileum in stimulating release of avian PP (APP) in turkeys. Although they differ in osmolarity, and are thus difficult to compare, amino acids appeared to be the best stimulant and HCl the next best. The stomach was the site in which nutrients were most likely to stimulate APP release. There was no significant difference between the responsiveness of the the ileum and duodenum. A control experiment in which blood was drawn but no intraluminal treatments were administered indicated that handling and bleeding caused depression of normal fasting plasma [APP].

Studies of methods for in situ observation of gastric motility in domestic turkeys.

The normal gastroduodenal contraction cycle of turkeys is believed to be controlled and coordinated by the myenteric plexus which lies just under the serosa of the muscular stomach. Methods which would permit direct application of chemical and physical stimuli to these gastric nerves were studied in intact and decerebrate turkeys using both radiographic and direct observations to monitor contraction cycles. In intact turkeys, general anesthetics (sodium pentobarbital, halothane; and ketamine hydrochloride) inhibited gastric motility. A local anesthetic (lidocaine hydrochloride) injected into the skin and abdominal muscles caused a depression of motility. In both intact and chronically decerebrate turkeys laparatomy (after local anesthetic in intact birds) and a neuromuscular blocking agent (gallamine triethiodide) also depressed gastric motility. Motility was slightly reduced by artificial respiration and exposure of the serosal surface of the stomach and intestines to air via an abdominal fistula.

A cephalic influence on gastric motility upon seeing food in domestic turkeys (Melagris gallopavo), great-horned owls (Bubo virginianus) and red-tailed hawks (Buteo jamaicensis).

Strain gage transducers were permanently implanted on the muscular stomachs of 13 turkeys, 3 great-horned owls and 2 red-tailed hawks to monitor gastric motility before, during and after eating. Following fasting, the sight of food resulted in significant increases in gastric contractile activity in all three species. Gastric motility further increased when the birds were allowed to eat. In raptors, however, a brief interruption in gastric motility occurred immediately after eating. This is apparently analogous to receptive relaxation which occurs in the stomach of mammals.

Diurnal cycles of gastric motlity in normal and fasted turkeys.

Strain gage transducers were chronically implanted on the muscular stomachs of 12 young turkeys to study diurnal patterns of gastric motility. Continuous recordings were made for several days before and after a period of two or three days of fasting. Pronounced diurnal cycles in gastric motility were observed in which the frequency and amplitude of gastric contractions were increased during the daylight and depressed during darkness. Fasting caused a reduction in both frequency and amplitude and, during fasting, the diurnal cycles were somewhat obscured. Motility improved upon refeeding and cycles were agina apparent. The diurnal cycles appeared to be at least partially regulated by an intrinsic biological rhythm.

Gastroduodenal electrical activity in turkeys.

Bipolar Ag/AgCl electrodes were implanted in the stomach and duodenum of 21 turkeys to study electrical activity in those organs. Intraluminal pressure changes were also monitored. For comparative purposes, electric slow waves were recorded from the stomach of turkeys. Although slow waves were recorded from the duodenum of turkeys, the waves were observed to wax and wane and were possibly not the major regulators of duodenal contractile activity. Several bursts of action potentials and several contractions usually occurred in the duodenum during one slow-wave cycle. Duodenal motility appeared to be totally coordinated with the gastric cycle. Impulses conducted over intrinsic nerves from a gastric pacemaker (15) were proposed as a possible mechanism for initiating and coordinating gastroduodenal motor activity.

Sites of organic acid production and pattern of digesta movement in the gastrointestinal tract of geese.

Sixteen geese were used to assess the movement of fluid and particulate digesta through their gastrointestinal tracts and to determine the diurnal variation in organic acid levels for the various segments of the tract. Fluid (polyethylene glycol and chronium-labeled ethylenediaminetetraacetic acid) and particulate markers (2 and 5 mm long) were administered with the meal. Animals were killed at given intervals after the administration of markers. The gastrointestinal tract was divided into nine segments for measurement of markers, pH, volatile fatty acids (VFA), and lactic acid contents. The data indicated a rapid evacuation of fluid marker from the foregut (crop, ventriculus, and proventriculus), while particulate markers were retained for extended periods of time. Retention of fluid marker was observed only within the cecum. Retrograde movement of particulate marker was demonstrated from the duodenum to ventriculus and proventriculus. Retrograde movement of fluid marker was observed from the cloaca to the colon, cecum, and distal third of the small intestine. However, particulate marker showed no retrograde movement in these segments of tract. Highest VFA levels were observed in the cecum. Retention of digesta and production of VFA within the colon were less than those noted for the dog, pig and pony. Lactic acid comprised less than 10% of the organic acids present in the gastrointestinal tract and were at their highest levels in the proximal and mid small intestine.