It is generally held to be true that smoking shortly before a meal leads to depression of hunger and appetite. It is also a common belief that strong pressure on the abdomen (" tightening the belt") decreases or relieves the hunger sensation, at least temporarily. We are now in position to test the correctness of these beliefs by decisive experiments as regards the influence of these measures on the objective hunger contractions and the .subjective hunger sensations.
Depression or inhibition of hunger by smoking is rendered probable by. the fact that, at least in man, anything which stimuli lates the sensory nerve-endings in the mouth and in the gastric jmucosa inhibits the gastric hunger contractions in direct proportion to the intensity of the stimulation. Smoking stimulates £he nerve-ending in the mouth in varying degrees, according to the kind of tobacco used. Smoking frequently involves stimulation of the nerve-endings in the gastric mucosa owing to the swallowing of saliva containing nicotine, oils, tannic acid, and other irritating substances. Smoking may also act on the hunger mechanism in a third way, that is, through absorption of nicotine and other products of the combustion. The third possibility has not been investigated. It is well established, however, that even small quantities of nicotine in the blood leads to nausea and vomiting. Nausea and vomiting are accompanied by atony of the gastric fundus, which insures absence of hunger contractions and hunger sensations.
The effects of smoking on the gastric hunger contractions were first studied on Mr. V., our young man with the permanent gastric fistula. In his case smoking (cigars) leads invariably to inhibition of the hunger contractions. But Mr. V. is not a habitual smoker. It is therefore possible that the results obtained on him were simply due to the condition of nausea or disgust that smoking usually produces in the novice and hence were not applicable to persons used to smoking.
The tests were repeated on several habitual smokers. So far as smoking influences the gastric hunger contractions this influence is in the direction of inhibition. This inhibition appears to depend on the intensity of stimulation of the nerve-endings in the mouth, a cigarette or "mild" cigar causing only slight inhibition, while a "strong" cigar or pipe causes complete and prolonged inhibition, even when the gastric hunger contractions are at their maximum.
If the cigar or pipe causes very strong stimulation of the nerve-endings in the mouth, the inhibition of the hunger contractions may continue from 5 to 15 minutes after the cessation of the stimulation. Thus even a brief period of smoking may suppress an entire hunger period.
The subjective sensation of hunger is diminished or abolished parallel with the gastric hunger contractions. But it seems to the authors that even a "mild" smoke diminished the sensation of hunger rather more than one might infer from the slight depression of the contractions. This is probably due to the deviation of attention, the smoking acting partly as a "counter-irritant."
Smoking inhibits the gastric hunger contractions. It is practically certain, even in the absence of direct experiments, that moderate smoking does not inhibit the gastric movements of digestion. The reason for this difference in the action of the same condition on the empty and on the filled stomach is not clear.
The experiments with constriction of the belt were made on three normal men. The tests were made with the subject standing up, sitting, and lying on the back, and at all stages of the gastric hunger contractions.
Strong contraction of the abdominal belt leads nearly always to inhibition of the gastric hunger contractions of weak or moderate strength, lasting from 5 to 15 minutes. The inhibition may be partial or complete, but in either case the hunger contractions reappear despite the continued pressure of the belt. This inhibition is obtained even when the belt constriction is moderate, so that no discomfort or pain is produced.
When the gastric hunger contractions are strong (the middle of a hunger period), constriction of the belt never causes complete inhibition. But so far as the increased abdominal pressure affects the hunger contractions, the influence is in the direction of inhibition. The individual hunger contractions are weakened without suffering much change in the rate. Frequently, however, even a belt constriction that caused considerable discomfort has practically no influence on the hunger contractions, particularly if the subject is lying down.
When the gastric hunger contractions are at their maximum in rate and amplitude, as is ordinarily the case near the end of a hunger period, no amount of belt constriction seems to influence the contractions. When this stage of the hunger period is reached the hunger pangs rim their normal course in the presence of even painful belt pressure.
All three subjects agreed that the belt constriction appeared' to diminish or interfere with the hunger sensation to a greater extent than seemed warranted from its effect on the hunger contractions. Several factors are probably involved in this discrepancy. (1) The belt constriction distracts the attention from the hunger impulses by stimulation of nerve-endings in the viscera, especially those of the peritoneum. (2) Strong pressure on the abdomen from without appears to induce, temporarily, a condition stimulating in a feeble way the complex sensation of satiety.
According to R. Lennhoff,1 hunger and appetite are appeased with a less quantity of food when the belt is constricted than when the intra-abdominal pressure is regulated solely by the tonus of the abdominal muscles. Lennhoff ascribes this to depression of hunger and appetite by the pressure of the belt. His observation is probably correct, but his explanation is erroneous. In a normal person the actual hunger contractions and hunger sensations are stopped by the first few morsels of food swallowed, while this may actually increase the appetite through stimulation of nerve-endings in the mouth and in the mucous membrane of the esophagus and stomach. This appetite sensation is gradually counteracted by the sensation complex of satiety, which depends in part on the distension of the stomach with corresponding readjustment of the tonus of the abdominal muscles. This feeling of fulness, which appears to be referred to the abdomen as a whole, is probably developed with less intake of food when the abdominal wall is mechanically prevented from relaxing owing to the pressure of the belt.
'Quoted in Jour. Amer. Med. Assoc., LX (1913), 41.
We have practically nothing but conjectures to offer in way of explanation of the mechanisms involved in these inhibitions of the gastric hunger contractions by strong pressure on the abdomen. Strong pressure on the abdomen causes temporary inhibition of the gastric hunger contractions in dogs, but the manipulation greatly disturbs them, and disturbance from any cause leads to a temporary inhibition of the empty stomach in dogs with the splanchnic nerves intact. In dogs with the splanchnic nerves sectioned on both sides strong pressure on the abdomen causes no distinct inhibition of the gastric hunger contractions. This points to the conclusion that belt constriction causes gastric inhibition, not by direct pressure on the stomach, but by direct stimulation of inhibitory nerves, or by mechanical (or sympathetic) stimulation of the adrenal glands, and through long reflexes. Belt constriction involves stimulation of cutaneous nerve-endings, but a gentle stimulation of the tactile nerve-endings in the skin alone does not lead to this inhibition. The afferent path of the reflex must therefore involve abdominal proprioceptors. The splanchnic nerves probably constitute the efferent path of the reflex. We do not wish to be understood as denying the existence of local inhibitory mechanisms that may be stimulated by mechanical manipulation of the abdominal organs, but our results indicate that strong belt constriction is not a sufficient stimulus for such local mechanisms.