Acid secretory responses to histamine and pentagastrin in conscious monkeys

A new in vivo method for repeatedly studying gastric acid secretion and other secretory parameters in awake guinea pig

A new model for measuring gastric secretory parameters in awake guinea pigs is described. A chronic cannula was surgically implanted in the stomach of each guinea pig. The rates of gastric secretion and changes in intragastric volume were measured using a dye dilution technique. In contrast to previous techniques in small laboratory animals, there was no collection of gastric juice via drainage, no oral intubation for aspiration was involved, no special or sophisticated equipment was used, no anesthesia was employed, and there was no stress associated with acute surgery. This method offers a valuable advantage by combining the chronic gastric cannula with a dye dilution technique in that the same animal can be used several times and finally, several gastric secretory parameters can be measured simultaneously. The animals were used from 3 weeks to 10 months after surgery and as many as 15 studies were performed on the same guinea pig. Samples were collected at 10-min intervals and analyzed for acid and dye concentration from which the onset and kinetics of gastric secretion were followed. Basal gastric secretion (11.8 +/- 1.6 mueq/kg/min; all mean +/- 1 SEM) was increased within 20 min after subcutaneous infusion of histamine (30 micrograms/kg/hr) and peaked by 40-60 min at a mean acid output rate of 41 +/- 3 mueq/kg/min. Histamine also increased the intragastric volume from 6.3 to 13.4 ml as it increased fluid output from 1.6 +/- 0.1 ml/10 min to 3.4 +/- 0.2 ml/10 min. The increase in acid output caused by histamine was inhibited by the H2-antagonists cimetidine (3 mumole/kg) and ranitidine at 0.5 mumole/kg. Omeprazole (1.2 mumole/kg), an H-K-ATPase inhibitor, almost abolished acid output under both basal and histamine-stimulated conditions. Thus, the present method is simple and suitable to study the physiology and pharmacology of gastric secretion in the guinea pig with a particular emphasis on the action of histamine. Furthermore, because of the species involved, there is also a significant economical advantage and the guinea pig can also be used as a potential model for studying experimental ulcer.

Stimulation of gastric acid secretion in the rhesus monkey

Similar maximal rates of gastric acid secretion are achieved with histamine and gastrin stimulation in human, dog, or cat, but gastrin produces higher rates than histamine in the rat. Gastric acid secretion was measured in seven nonsedated, alert, chaired rhesus monkeys (Macaca mulatta). Dose-response studies were performed using intravenous histamine or tetragastrin. These studies showed histamine to be a much more efficacious and more potent stimulant of gastric acid secretion than tetragastrin in the monkey. Both histamine and tetragastrin had similar potency and efficacy in the dog, while tetragastrin, pentagastrin, and hog heptadecapeptide were similarly less active than histamine in the monkey. Background carbachol (4 micrograms/kg/hr) did not affect the histamine or tetragastrin dose-response curves. Histamine stimulation with background tetragastrin (64 micrograms/kg/hr) did not produce a dose-response curve statistically different from histamine alone. Tetragastrin stimulation with background histamine (60 micrograms/kg/hr) increased the tetragastrin dose-response curve, with a probable additive effect. We conclude that the rhesus monkey differs from cat, dog, and man in that gastrin and its analogs are not able to stimulate maximal acid secretion to the level achieved by histamine.

Ultradian rhythms of gastric acidity

Measurements of gastric pH and hydrogen ion concentration were made serially for six hours in five rhesus monkeys. Both pH and hydrogen ion concentration showed rapid fluctuations with periods approximating 90 minutes. These rhythms persisted in the face of continuous infusion with Pentagastrin, indicating that while gastrin release is sufficient to stimulate acid secretion, it is not the only mechanism of acid control.

A primate model for enteral nutrition by tube

To establish an animal model for the controlled study of enteral nutrition by tube, five adult chair-adapted primates (Macaca fasicularis) had gastrostomy and jejunostomy tubes placed for the delivery of a modified protein isolate diet. Following 7 days of postoperative depletion with a hypocaloric infusion of dextrose (20 kcal, 0 g N/kg/day), the animals were repleted for 10 days with tube feedings (124 kcal, 0.73 g N/kg/day). There was no operative mortality or morbidity and each animal demonstrated conversion to anabolism by significant weight gain, positive nitrogen balance, and net protein synthesis as determined by [15N]glycine protein turnover rates. Significant correlation was found between caloric intake and nitrogen balance at the level of nitrogen provided in this diet (r = 0.88, p less than 0.05). This model was found to be well suited for the surgical and nutritional techniques required for the long-term study of enteral nutrition by tube.

Hyperalimentation in primates. A nutritional model

To establish the subhuman primate as an effective laboratory animal in parenteral nutrition research, 18 male macaque monkeys were adapted to chronic chair restraint and maintained on intravenous nutrition for 1- and 2-week periods. The animals remained in the restraint chairs for 11.6 +/- (2.3) weeks and the inferior vena cava catheters remained for 53 +/- (7.8) days. Catheter and metabolic complications during intravenous nutrition infusion were few and morbidity was low. The animals maintained weight, serum albumin, and serum transferrin levels as well as a positive nitrogen balance during the study period. The macaque is a highly suitable model for nutritional studies requiring a controlled environment during long-term studies.

Gastric antisecretory effects of E prostaglandins in Rhesus monkeys

The gastric antisecretory actions of prostaglandin E1 methyl ester (PGE1ME) and prostaglandin E2 (PGE2) were evaluated in unanesthetized gastric fistula rhesus monkeys. Basal and stimulated gastric secretory studies were conducted. Multiple subcutaneous injections of either histamine or pentagastrin were given hourly for four consecutive hours. When a constant plateau of gastric secretion was reached, the PGs were administered as a single intravenous bolus at doses of 10-100 mug/kg. PGE1ME inhibited basal, histamine- and pentagastrin-stimulated gastric secretion. PGE2 was found to inhibit the histamine- stimulated gastric secretion. The PGs showed greater sensitivity to the inhibition of acid concentration rather than the volume of secretion. The PGs signfiicantly altered gastric juice concentration of hydrogen and sodium ion inversely, while potassium and chloride concentration were not altered. These experiments suggest that the rhesus monkey is a useful species for studying the gastric antisecretory effects of E prostaglandins.

Gastric antisecretory actions of (15S)-15-methyl prostaglandin E2 methyl ester and natural prostaglandin E2 in rhesus monkeys

The gastric antisecretory actions of (15S)-15-methyl prostaglandin E2 methyl ester (Me-PGE2) and Prostaglandin E2 (PGE2) were evaluated in the unanesthetized gastric fistula rhesus monkey. Secretion was submaximally stimulated by multiple subcutaneous injections of histamine acid phosphate given every hour for four consecutive hours. When a steady-state plateau of gastric secretion was reached, the PG's were administered as a single bolus dose either intravenously (i.v.) or intragastrically (i.g.). Both PG's inhibited histamine-stimulated gastric secretion. The PG's showed greater sensitivity in inhibiting acid concentration while not affecting volume output. Active i.v. and i.g. antisecretory doses of ME-PGE2 ranged from 3 to 10 mug/kg, while PGE2 showed significant antisecretory activity at i.v. bolus doses of 30-100 mug/kg and i.g. bolus dose of 1.0 mg/kg. Thus, Me-PGE2 is estimated to be at least 10 and 300 times more potent than PGE2 by the i.v. and i.g. administration routes, respectively. These findings indicate that the rhesus monkey shows some similarities to man in responsiveness to gastric secretory inhibition by E-prostaglandins.