Biomedical subjects

A M Merritt

Publications and source records attributed to A M Merritt.

At least 37 records · Page 2Linked to original sources

PubMed1998

Histamine-induced gastric acid secretion in horses.

OBJECTIVE: To determine gastric secretory responses in horses treated with histamine and to determine the dose of histamine needed to elicit maximal gastric secretion. ANIMALS: 6 adult horses with an indwelling gastric cannula. PROCEDURE: Gastric contents were collected in 15-minute periods, and volume, pH, hydrogen ion concentration, hydrogen ion output, sodium concentration, and sodium output were determined. Values were determined without any treatment (baseline), after administration of pyrilamine maleate (1 mg/kg of body weight, i.v., given during a 15-minute period), and during 1-hour infusions of histamine at 3 rates (7.5, 15, and 30 microg/kg/h, i.v.). RESULTS: Volume and hydrogen ion concentration of gastric contents and hydrogen ion output were significantly increased, compared with baseline values, during histamine infusion. Mean hydrogen ion concentration and hydrogen ion output were significantly greater during infusion of histamine at a rate of 15 or 30 microg/kg/h than at a rate of 7.5 microg/kg/h. Sodium concentration was significantly decreased, compared with baseline value, during histamine infusion, but sodium output was unchanged. CONCLUSIONS: Histamine at doses of 15 and 30 microg/kg/h, i.v. stimulated maximal gastric secretion in horses. Histamine appeared to induce only parietal secretion. CLINICAL RELEVANCE: This study provides additional information related to equine gastric physiology, which may benefit further understanding of the pathogenesis of peptic ulcer disease.

Animals↗

PubMed1996

Effect of aluminum hydroxide/magnesium hydroxide antacid and bismuth subsalicylate on gastric pH in horses.

OBJECTIVE: To assess the effect of aluminum hydroxide/magnesium hydroxide antacid and bismuth subsalicylate on gastric pH in clinically normal horses and to develop guidelines on the use of these agents for treatment of peptic ulcer disease in horses. DESIGN: Prospective, randomized, controlled trial. ANIMALS: 5 clinically normal adult horses with chronically implanted gastric cannulas. PROCEDURE: Each horse received all 5 treatments (30 g of aluminum hydroxide/15 g of magnesium hydroxide, 12 g of aluminum hydroxide/6 g of magnesium hydroxide, 10.5 g of bismuth subsalicylate, 26.25 g of bismuth subsalicylate, and 5% methylcellulose control) with only 1 experiment performed each day. Gastric pH was measured via a glass electrode inserted through the gastric cannula for 1 hour before treatment and continued for 2 hours after treatment. Food or water was not given to the horses during the experiment. Measurements of gastric pH obtained during posttreatment hours were compared with pretreatment gastric pH values. RESULTS: Only a dose of 30 g of aluminum hydroxide/ 15 g of magnesium hydroxide resulted in a significant increase in gastric pH over baseline or control values. Mean pH was 5.2 +/- 0.62 and 4.59 +/- 0.48 for posttreatment hours 1 and 2, respectively. CLINICAL IMPLICATIONS: Oral administration of 30 g of aluminum hydroxide/15 g of magnesium hydroxide to adult horses should result in a mean hourly gastric pH > or = 4.0 for at least 2 hours.

Administration, Oral↗

PubMed1996

Evaluation of cecal ligation as a model of mucoid enteropathy in specific-pathogen-free rabbits.

Mucoid enteropathy is a serious disease of rabbits, the cause of which is unknown. Ligation of the cecum has been reported to cause a mucoid enteropathy-like syndrome in 70% of conventional rabbits. The goal of this study was to evaluate this model of mucoid enteropathy in Pasteurella-free, coccidia-free rabbits for use in future studies. Five rabbits served as unoperated controls (group 1). Eight rabbits underwent ligation of the cecum, with large vessels and nerves spared (group 2). In six rabbits the distal branch of the ileocecocolic vessels and nerve were incorporated into the cecal ligature (group 3). At necropsy 3 to 5 days after surgery, all group-3 rabbits had copious amounts of clear, gelatinous mucus in the colon. Only one group-2 rabbit had grossly evident mucus hypersecretion, whereas none of the group-1 rabbits did. Group-3 rabbits had areas of necrosis in the cecum; this was not seen in group-1 or group-2 rabbits. Rabbits of groups 2 and 3 had inflammation of the distal portion of the colon. In specific-pathogen-free rabbits cecal ligation alone did not reliably stimulate mucus hypersecretion but induced a disease similar to natural mucoid enteropathy. Cecal ligation including vessels provided a reproducible syndrome of mucus hypersecretion; however, the severe cecal necrosis was not consistent with the naturally acquired disease.

Animals↗

PubMed1996

Mucus secretagogue activity in cecal contents of rabbits with mucoid enteropathy.

Cecal filtrates from rabbits with cecal ligation-induced mucoid enteropathy have been reported to cause goblet cell hyperplasia in intestinal explants. This study was performed to see whether such filtrates would stimulate mucus secretion from intestinal explants. Filtrates were prepared from cecal contents of five control rabbits, five rabbits that had undergone cecal ligation, and five rabbits that had had the distal branch of the ileocecocolic vessels and nerve incorporated into the cecal ligature. After incubation of each with ileal and colonic explants from five healthy rabbits, the amount of mucus in the media/filtrate solution was measured with an enzyme-linked lectin assay. Significantly (P < 0.05) more mucus was secreted by colonic explants in the presence of cecal filtrates from either of the cecal ligation groups compared with controls. With pooled filtrates from each group, these results were confirmed by measuring secretion of radiolabeled mucus from explants that had been preincubated with [3H]glucosamine. The secretagogue activity was found to be precipitable by 85% ammonium sulfate and destroyed by heat treatment (100 degrees C for 30 min) or acid treatment (pH 1.0 for 30 min). Very little, if any, secretagogue activity was present in cecal vein serum. The results support the hypothesis that the cecal contents of rabbits with cecal ligation-induced mucoid enteropathy stimulate mucus secretion from colonic explants taken from healthy rabbits.

Animals↗

PubMed1996

Effect of omeprazole on sodium and potassium output in pentagastrin-stimulated equine gastric contents.

OBJECTIVE: To better characterize the source of the large nonparietal secretory response to pentagastrin (PG) expressed in gastric contents of cannulated horses. ANIMALS: Adult cross-bred horses: 4 geldings and 1 mare. PROCEDURE: Horses were prepared by surgical insertion of a silastic gastric cannula from which gastric contents after feed was withheld could be continuously collected by gravity drainage. During experiments, the horses were lightly restrained in stocks, the gastric cannula was opened, and a catheter was inserted into a jugular vein. Over the next 5 hours, gastric contents were collected in 15-minute aliquots for which volume, pH, [Na+], and [K+] were measured. During the first hour, treatment was not administered. At the start of the second hour, either 0.5 mg of omeprazole (OME; dissolved in glycerol formal)/kg of body weight, or 0.9% NaCl (PSS) of comparable volume, was given IV at random as a bolus. At the start of the third hour, IV infusion of PG (6 micrograms/ kg/h) was started and continued for the next 2 hours. RESULTS: The response to PG in the PSS-treated horses was similar to that previously seen-significant decrease in pH and increase in volume of gastric contents, and no change in [K+] and [Na+], but a modest volume-related increase in their respective outputs. After OME treatment, pH of the contents increased sharply and remained between 5 and 6 throughout PG infusion. Sodium concentration significantly increased after OME and virtually paralleled the pH response throughout the rest of the experiment; volume of gastric contents significantly increased in response to PG infusion and resulted in a significant increase in Na output. There was no change in K output in OME-treated animals. CONCLUSIONS: PG induces a marked, nonparietal, secretory response into the gastric contents of cannulated horses. The volume and [Na+] of this response was maintained after pretreatment with OME, although the pH of the contents became basic, indicating that this nonparietal response is not mediated by an OME-sensitive proton pump.

Animals↗

PubMed1996

Effect of bethanechol or erythromycin on gastric emptying in horses.

OBJECTIVE: To investigate the prokinetic effect of bethanechol and erythromycin in the upper gastrointestinal tract of healthy horses by measuring the gastric emptying (GE) rate of a radioactive meal. ANIMALS: 4 healthy adult horses. PROCEDURE: After food was withheld for 12 hours, horses were given 370 MBq of 99mTc-labeled sulfur colloid incorporated into egg albumen and 37 MBq of 111In-labeled diethyltriaminepentaacetic acid in 120 ml of water via nasogastric intubation. Intravenously administered treatments were 0.9% NaCl solution, erythromycin (0.1 or 1.0 mg/kg of body weight), or bethanechol (0.25 mg/kg). All drugs were given in 10 ml of 0.9% NaCl solution. Dual-phase scintigraphic images were obtained by use of a gamma camera. The best-fit function was determined for each study, and the resultant curves were then analyzed by use of least squares nonlinear regression. Two variables, time to 50% emptying of the stomach (T-50) and slope of the emptying curve, were derived from the calculated power exponential equation. CONCLUSIONS: Treatment had a significant (P < 0.05) overall effect on T-50 of solid-phase GE. The T-50 of bethanechol (30.09 +/- 10.01 minutes), erythromycin at 0.1 mg/kg (59.08 +/- 10.01 minutes), and erythromycin at 1 mg/kg (60.50 +/- 10.01 minutes) were significantly shorter than T-50 after saline administration (89.97 +/- 10.01 minutes). There was a trend (P = 0.09) for the slope of solid-phase GE of bethanechol and erythromycin (0.1 mg/ kg; P = 0.37) to be steeper than that of saline solution. For liquid-phase GE, the T-50 and the slope of bethanechol differed significantly (P < or = 0.05) from those for saline solution. CLINICAL RELEVANCE: Bethanechol and erythromycin significantly increased solid-phase GE in healthy horses and may have value for use as prokinetic agents in certain gastrointestinal tract diseases.

Animals↗

PubMed1995

Equine pelvic flexure myoelectric activity during fed and fasted states.

The pelvic flexure is the midpoint of the equine large colon that marks the junction of dorsal and ventral components. Previous studies of intraluminal pressure in this region indicate that it could be an important motility control center. The present study was undertaken to expand our knowledge of normal myoelectric activity around the pelvic flexure region. Eight bipolar silver wire electrodes were surgically fixed at 5-cm intervals to the colonic serosa of five adult horses, starting 30 cm oral to the pelvic flexure on the left ventral colon and ending 15 cm aboral to the pelvic flexure on the left dorsal colon (LDC). Recordings of myoelectric activity were done after feed had been withheld for 20 h or when the horses had been allowed to eat hay up to the time of the recording session. The activity was recorded on a polygraph, digitized, processed through a commercial graphics software package, and stored on magnetic tape for later analysis. Action potential activity was basically separated into long spike bursts (LSB) that were > or = 4 s duration and short spike bursts (SSB) that were < 4 s duration and quantified by a software program developed exclusively for the equine large intestine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Influence of an abrupt change in diet on antroduodenal myoelectric activity in lactating cattle.

Effects of a change from a diet composed primarily of forage to a diet composed primarily of concentrate on abomasal antral and duodenal motility were assessed in 5 lactating Holstein cows. Antroduodenal motility was measured by use of 8 silver electrodes sutured to the abomasum and duodenum, and abomasal emptying was assessed by continuous measurement of intraduodenal pH. Both diets were fed to achieve a daily dry matter intake of 2.7 kg/100 kg of body weight. The abrupt change in diet did not alter antroduodenal myoelectric activity or abomasal emptying. Initiation of phase III of the migrating myoelectric complex in the proximal portion of the duodenum corresponded with a decrease in abomasal antral spiking activity and an increase in intraduodenal pH. Results suggest that a high concentrate diet alone does not adversely affect antroduodenal motility in adult dairy cattle.

Abomasum↗

PubMed1991

Tumor necrosis factor activity in the circulation of horses given endotoxin.

Serum and plasma from horses injected with endotoxin was examined for cytotoxic activity. Each of the cell lines, L929 and WEHI 164 clone 13, was sensitive to the cytotoxic effects of equine serum; however, a precipitation artifact caused by the use of isopropanol in the WEHI assay limited the use of this assay to samples containing less than 2 mg of protein/ml. In foals treated with a sublethal IV bolus of 5 micrograms of lipopolysaccharide (LPS)/kg and in adult horses given a low-dose continuous infusion of LPS (30 ng/kg/h for 4 hours), cytotoxic activity was detected in all serum or plasma samples taken between 30 minutes and 4 hours after LPS infusion began. In horses given either continuous or bolus LPS infusions, circulating cytotoxic activity peaked at 1 to 2 hours before decreasing sharply. The onset of pyrexia after LPS infusion coincided with the appearance of circulating cytotoxic activity, but the temperature remained high, even after cytotoxic activity disappeared. Treatment of horses with flunixin meglumine (1 mg/kg) appeared to blunt the pyrexic effect of low-dose continuous LPS infusion, but had no significant effect on circulating cytotoxic activity. Incubation of serum samples with an antibody raised against a portion of human tumor necrosis factor (TNF) resulted in the removal of greater than 90% of serum cytotoxicity, suggesting strongly that the cytotoxic activity was attributable to TNF. These findings are consistent with the hypothesis that TNF is an early acting mediator of the effects of endotoxin in the horse.

Animals↗

PubMed1990

Decreased erythrocyte potassium concentration associated with exercise-related myopathy in horses.

To investigate the possibility that a disorder of potassium balance may have a role in the development of equine rhabdomyolysis, the potassium concentration within erythrocytes (RBC [K+]) and plasma (P [K+]) was measured in 3 groups of horses: group 1, eight 2-year-old fillies that had postexercise muscle soreness within 48 hours of sample collection; group 2, ten 2-year-old fillies subjected to identical management and training conditions (as fillies of group 1) and that did not have signs of myopathy; and group 3, 32 yearlings of both sexes on the farm of origin of groups 1 and 2 that were pastured and not in training. Creatine kinase activity in serum from horses of groups 1 and 2 was also measured. The mean P [K+] was not significantly different between groups, whereas the mean RBC [K+] was significantly (P less than 0.01) lower in group-1 fillies vs group-2 fillies and group-3 horses. Group-1 fillies also had markedly high serum creatine kinase activity. Results of the study revealed significantly lower RBC [K+] in horses that had had signs of myopathy within the preceding 48 hours. This does not prove a causal relationship between RBC potassium depletion and myopathy, but does suggest that decreased RBC [K+] may be observed in horses with exercise-related myopathy.

Animals↗

PubMed1990

Properties of pteroylpolyglutamate hydrolase in pancreatic juice of the pig.

The function of pteroylpolyglutamate hydrolase (PPH) of pancreatic secretion in the hydrolysis of dietary polyglutamyl folates (PteGlun) in humans is unclear. In this study, PPH was detected in pancreatic juice collected from pigs during both fasting and postprandial conditions. The secretion of PPH was markedly increased following feeding. Pancreatic PPH showed the following characteristics: 1) endo/random hydrolysis of gamma-glutamyl peptide bonds of Pte-Glun substrates, yielding folic acid as the terminal product; 2) maximum activity at pH 4.0-4.5 and maximum stability at pH 7.0; 3) stimulation of activity by Zn2+ and 2-mercaptoethanol; 4) Km values for pteroyltriglutamate (PteGlu3) of 28.7 microM at pH 4.0 and 9.1 microM at pH 5.0; 5) apparent molecular weight of 29,000; and 6) isoelectric point within the range of 8.5-9.0. On the basis of PPH activity, volume of the postprandial secretion and pH profile of enzyme activity, it is suggested that pancreatic PPH may act in vivo in folate digestion and absorption to initiate the deconjugation of dietary PteGlun prior to the action of jejunal brush border PPH.

Animals↗

PubMed1990

Basal and pentagastrin-stimulated gastric secretion in young horses.

Equine gastric secretion was studied using a gastric cannula model after fasting (basal) and pentagastrin infusion. Gastric secretory rate, pH, osmolality, and electrolyte concentrations and outputs were determined over a 5-h period. Dose-response tests estimated that the maximally effective intravenous dose of pentagastrin was between 3 and 6 micrograms.kg-1.h-1. Basal secretory rate was 278 +/- 29 (SE) ml/15 min, and the pH was 2.00 +/- 0.31. Pentagastrin infusion at 6 micrograms.kg-1.h-1 increased secretory rate to 533 +/- 60 ml/15 min and decreased pH to 1.41 +/- 0.11. Basal gastric acid concentration and output were 38 +/- 5 meq/l and 211 +/- 36 mu eg.kg-1.h-1, respectively. Pentagastrin increased acid concentration to 60 +/- 5 meq/l and acid output to 474 +/- 61 mu eq.kg-1.h-1. Gastric fluid osmolality remained hypotonic during both basal and pentagastrin conditions. Sodium concentration remained high in comparison with hydrogen ion concentration, and sodium output increased during pentagastrin infusion. Equine gastric secretion did not attain maximal acid concentrations nor the marked drop in pH, which has been reported for other monogastric species. These data suggest that in the horse a large nonparietal component exists that modifies parietal secretions and is increased by pentagastrin stimulation.

Animals↗

PubMed1990

Comparison of the effects of an isosmolar and hyperosmolar oral rehydrating solution on the hydration status, glycemia and ileal content composition of healthy neonatal calves.

Isosmolar oral rehydrating solutions (ORS) used to treat diarrheic calves are low in energy. In contrast, hyperosmolar ORS may have a dehydrating effect. This study was designed to compare the net water and glucose absorption from the small intestine of normal calves given isosmolar or hyperosmolar ORS. Six calves were used for the experiment. A reentrant ileal cannula was implanted surgically. Each calf was fed with either the isosmolar or the hyperosmolar solution. The next day, the second solution was given. Both contained chromium EDTA as a nonabsorbable marker. Changes in the hematocrit, total plasma protein, plasma osmolality, plasma glucose concentration, and ileal volume, osmolality, glucose content, and chromium concentration were monitored for 10 hours. The only statistically significant difference was in the post-feeding plasma glucose level: it peaked at the higher level (p less than 0.05) in calves fed the hyperosmolar solution. In normal calves, the hyperosmolar ORS had no effect on the hydration or on the small intestinal fluid composition.

Animals↗

PubMed1989

Effect of butorphanol on equine antroduodenal motility.

Six healthy six to eight-month-old horses were surgically prepared with Ag bipolar electrodes sutured to the gastric antrum and duodenum. Leads from the electrodes were exteriorised through a stab incision in the flank. During experimental sessions the horses were lightly restrained in stocks and electrode leads were connected to a physiograph to record antroduodenal myoelectrical activity. Intravenous (i.v.) injection of 0.05 mg/kg bodyweight (bwt) of the opioid agonist/antagonist, butorphanol was followed within 2 to 3 mins by a normal appearing period of repetitive spike activity, or phase III, of the migrating motor complex (MMC) on the duodenum. This was followed by a period of no spike activity, or phase I, of the MMC and then resumption of intermittent spike activity, or phase II, of normal duration. Pre-treatment with 15 micrograms/kg bwt of the non-selective opioid antagonist, naloxone, or with 1 mg/kg bwt of the alpha 2-adrenergic antagonist, tolazoline, did not block the myoelectrical response to butorphanol. It was concluded that a dose of butorphanol that has effective analgesic effects in a colicky horse resets the antroduodenal MMC without causing undesirable effects on antroduodenal motility. This particular effect of butorphanol might not be mediated by either a2-adrenergic or opioid receptors, although the latter question needs further investigation.

Adrenergic alpha-Antagonists↗

PubMed1989

Effect of xylazine treatment on equine proximal gastrointestinal tract myoelectrical activity.

Five 5 to 6 month old horses were surgically prepared with silver electrodes sutured to the serosa of gastric antrum, duodenum and proximal portions of the jejunum. Normal migrating motility complex (MMC) periodicity was determined during daytime hours in horses that were fed and horses from which food was withheld for 24 hours. Periodicity was defined as time span from the end of one period of regular spike activity (RSA) to the end of the next RSA in the MMC. The periodicity was 120.5 +/- 9.5 (SEM) minutes in horses from which food was withheld, and was 125.7 +/- 20.3 minutes in horses fed hay free choice. Coincident with each duodenal RSA, antral spike activity ceased. Xylazine (0.25 and 0.5 mg/kg), given IV during the period of intermittent spike activity of the MMC to either fed or unfed horses induced, within 2 minutes, a RSA complex in the duodenum that migrated to the proximal portion of the jejunum. This was followed by a period of no spike activity of normal duration, which proceeded on to a period of intermittent spike activity of varying duration to complete the MMC cycle. Pretreatment IV administration of an alpha 2-adrenergic antagonist, tolazoline (1 mg/kg) also provoked a RSA complex, but blocked the xylazine effect. The results indicated that xylazine resets the duodenal MMC in the horse, but does not seriously disrupt proximal gastrointestinal tract motility, and that control of MMC periodicity in this region probably involves more than alpha 2-adrenergic receptors.

Animal Feed↗

PubMed1988

Milk feeding and xylazine treatment induce increased antroduodenal motility in young cattle with opposite effects on duodenal digesta flow rate.

Antroduodenal myoelectrical activity and duodenal digesta flow rate in young cattle were assessed by implanted nichrome wire electrodes and reentrant duodenal cannulation with interposed flow-meter. In addition, a small glass electrode was inserted through a duodenal cannula to continuously measure the pH of duodenal contents. When eating only hay ad libitum, the duodenal myoelectrical activity showed the usual migrating myoelectrical complex (MMC) pattern. Duodenal contents pH rose sharply at the end of a period of repetitive spike activity (RSA), or phase III, from pH less than 2 to greater than 5 and remained high through most of the subsequent period of no spike activity (NSA), or phase I, during which there was no antral spiking and no flow of duodenal contents. Feeding milk (pH 6.5) caused a marked increase in antroduodenal spike activity and intraduodenal flow rate, with a concomitant rapid rise in duodenal contents pH from 1.8 +/- 0.3 (SEM) to 5.0 +/- 0.2 which then slowly declined over the next few hours. Within 5 min after the administration of the alpha 2-adrenergic agonist xylazine (25 and 50 micrograms/kg intramuscular), there was a significant increase (P less than 0.05) in antroduodenal spike frequency and a concomitant marked drop in intraduodenal flow rate with a sustained low pH of intraduodenal contents. The results suggest that: (1) continuous measurement of proximal duodenal pH adds a useful dimension to documenting relationships between antroduodenal myoelectrical activity and duodenal digesta flow rate; and (2) increased spike activity in the antroduodenal region does not necessarily indicate an increased duodenal flow rate is occurring.

Animal Feed↗

PubMed1988

Avian mycobacteriosis in three horses.

The clinical, bacteriologic and pathologic findings of three adult horses suffering from avian tuberculosis are presented. Chronic weight loss and hypoproteinemia were pertinent clinical abnormalities in all three horses. Gross pathologic lesions were characterized by chronic enterocolitis with mesenteric lymphadenopathy in two horses and hepatic granulomas in the third horse. The microscopic diagnoses were chronic, non-caseating granulomatous enterocolitis, and necrotizing, non-mineralizing granulomatous hepatitis, respectively. All three horses had granulomatous lymphadenitis of mesenteric lymph nodes with varying degrees of non-mineralizing, coagulation necrosis. Various serotypes of the Mycobacterium avium-intracellulare complex were isolated from selected tissues and feces.

Animals↗

PubMed1987

Effect of ranitidine on gastric acid secretion in young male horses.

Gastric cannulas were placed surgically in 5 young male horses. After a 2-week recovery period, horses were studied once a week. Horses were fasted for 24 hours, and gastric fluid output was collected for 5 continuous hours. Volumes were recorded every 15 minutes, and pH and hydrogen ion concentration were determined in an aliquot from each period. In 10 basal experiments, using 5 horses, volume, pH, and hydrogen ion concentration were continuously variable. Mean acid output was 45.1 +/- 2.02 microEq/15 min/kg (mean +/- SEM). In 6 experiments, using 3 horses, 0.5 mg of ranitidine/kg of body weight, given as an IV bolus after a 1-hour basal collection, significantly (P less than 0.02) inhibited hourly total acid output for 4 hours, but did not significantly change pH. The cannulation technique was done without complications, and horses tolerated the cannula for several months. Seemingly, the horse has a continuously variable gastric acid secretion, and histamine type-2 receptors have a role in this process.

Animals↗