Accelerated gastric emptying in VMH-lesioned rats is secondary to excess weight gain

This experiment evaluates the hypothesis that an accelerated rate of gastric emptying accounts for the hyperphagia and obesity after lesions of the ventromedial hypothalamus (VMH). Gastric emptying was measured for 16 days after the production of VMH lesions in rats maintained either ad libitum or on restricted eating. Only ad libitum VMH-lesioned rats demonstrated faster than normal rates of emptying. However, VMH rats maintained at control weights showed normal rates of gastric emptying and, even in ad libitum rats, accelerated emptying was not apparent immediately after lesions. These findings indicate that changes of emptying are not a primary effect of VMH lesions but that this dysfunction develops secondarily as a consequence of excess eating and weight gain. Measurement of stomach secretions demonstrated, however, that VMH lesions did result in an immediate and direct effect on gastric secretion. These findings mitigate the importance of gastric emptying in the etiology of the VMH syndrome. Other data consistent with this conclusion are reviewed.

THE ACID-BASE COMPOSITION OF GASTRIC SECRETIONS

The chief inorganic factors in secretions obtained from isolated pouches constructed in the fundus and in the pyloric antrum of the cat's stomach were found to be chloride ion and fixed base. In a series of samples obtained from the fundic pouch, chloride ion was approximately stationary at 165 cc. 0.1 N per 100 cc. During digestion of food in the stomach, secretions from the pouch contained fixed base in amounts varying considerably from an average of 47 cc. 0.1 N per 100 cc. Material allowed to remain in the pouch after the completion of food digestion in the stomach showed an increasing content of fixed base, to as much as 140 cc. 0.1 N per 100 cc. A stationary total ionic content of secretions of the fundus is thus seen to be sustained by the chloride ion concentration, and changes in hydrogen ion concentration to be caused by variation of fixed base. The differing amounts of fixed base found are regarded as probably due to admixture of a mucous secretion with the juice from the fundic glands. The alkaline secretion taken from a pyloric pouch contained fixed base in excess of chloride ion. Variation of fixed base in the secretions from the fundic pouch were found to be referable to change in sodium content, the smaller factor, potassium, remaining approximately constant at about the value found in material from the pyloric pouch. This suggests that the mucous secretion of the fundus has the same composition as that produced by the pyloric antrum. These data will serve to explain the extensive withdrawal of fixed base, as well as of chloride ion, from the blood plasma in the presence of circumstances causing a continued loss of stomach secretions.

The Antivenomous Properties of the Bile of Serpents and other Animals; and an Explanation of the Insusceptibility of Animals to the Poisonous Action of Venom introduced into the Stomach

In a paper communicated to this Society I stated that, when, introduced into the stomach of an animal, serpents' venom produces no obvious injury, even when the quantity is so large as to be sufficient to kill 1000 animals of the same species and weight if the venom were injected under the skin. The failure of so highly toxic a substance to produce poisoning when it is administered by the stomach might be due to chemical changes produced upon it by the secretions of the stomach and intestines, or to non-absorbability into the blood from the stomach and intestines. It is already known that the toxicity of venom is not materially reduced by gastric digestion. Although at first sight incompatible with the innocuousness of stomach administration, this fact is not in reality a contradiction of it, for the absorbing power of the stomach for many organic substances—even for strychnine—has been shown to be extremely slight, and their entrance into the circulation appears to occur not in the stomach but in the intestines.As serpents' venom introduced into the stomach is not rendered innocuous by the stomach secretions, while, notwithstanding, it fails to cause poisoning, it may be assumed that the stomach walls are incapable of absorbing it. If, like other poisons, it can be absorbed from the intestines, the explanation of the failure to produce toxic symptoms when it is administered by the stomach might depend on a chemical or physiological destruction of its toxic properties by some substance or substances which it encounters soon after entering the intestinal canal, and most probably, therefore, by the bile or the pancreatic secretion.