Effects of enteric microbial overgrowth on small intestinal ultrastructure in the rat

The ultrastructural effects of bacterial proliferation in the upper gastrointestinal tract induced by intraperitoneal injections of mecamylamine HCl were investigated in rats. We found increased populations of nonspecific enteric bacteria in the lumen of the upper small intestine and ultrastructural abnormalities in the absorptive epithelial cells, including increased numbers of lysosomal vacular structures, fused microvilli and dilated endoplasmic reticulum. The bacteria did not penetrate into the damaged mucosal cells and so actual cytoplasmic infiltration is apparently not required in order to cause these ultrastructural changes. The alterations were not merely due to the pharmacologic agent we used, mecamylamine, since rats with subnormal numbers of enteric bacteria in the upper small intestine, whether subjected to the course of the drug or not, did not display the ultrastructural changes noted above. Concomitant with increased numbers of enteric bacteria in the small intestine, there were increased concentrations of deconjugated bile salts and decreased absorption of glucose. These findings are compatible with the following hypothetical sequence of pathogenesis: mecamylamine leads to intestinal stasis leads to bacterial overgrowth leads to deconjugation of the bile salts leads to ultrastructural alterations.

Cardiovascular responses to injections of cholinomimetic drugs into the cerebral ventricles of unanaesthetized dogs

1. The cardiovascular and behavioural effects of cholinomimetic drugs injected through a cannula chronically implanted into a lateral cerebral ventricle were examined in unanaesthetized dogs.2. Acetylcholine (ACh) (10-20 mug) produced an increase in arterial pressure and heart rate, the dogs became more alert, moved their heads, licked and swallowed and then became drowsy.3. The responses to ACh were potentiated by intraventricular physostigmine (5 mug), were abolished by intraventricular atropine (100 mug) but were unaffected by intraventricular mecamylamine (250 mug). The responses to ACh were reproducible on any one day if injections were given again after a 30 min interval but tolerance developed when ACh was injected repeatedly over periods of several days.4. Methacholine (40 mug) produced similar behavioural and cardiovascular effects to ACh but of a longer duration. The responses to methacholine were abolished by intraventricular atropine (100 mug).5. Nicotine (20-60 mug) produced a biphasic cardiovascular response of an initial brief pressor response and tachycardia followed by a secondary increase in arterial pressure and heart rate which was greater in magnitude and duration. The secondary cardiovascular effects were associated with restlessness and vomiting.6. The responses to nicotine were abolished by prior injection of mecamylamine (250 mug) but were unaffected by atropine (100 mug). The responses to nicotine were not reproducible if injections were repeated on the same day but could be again produced if a few days were allowed to elapse between injections.7. An increased heart rate occurred during the pressor response to the cholinomimetic drugs but when a comparable pressor response was produced by intravenous infusion of noradrenaline in the same unanaesthetized dogs pronounced reflex bradycardia resulted.8. The results indicate that the activation of both muscarinic and nicotinic cholinergic mechanisms leads to cardiovascular and behavioural effects in the conscious dog although the site of action and peripheral mechanisms have not been determined.