This is not a discussion of the millions who have now adopted the high-protein, low-carbohydrate diet popularized by Dr. Robert Atkins. The high protein diet described belongs to the Burmese python and new findings based on research with animals reveal the physiological processes that occur with digestion of a high protein fare. Accordingly, this animal's emergence as a laboratory animal may have contributed to an earlier resolution in the heated debate that was carried on about the safety of the high protein diet.
Background
The Burmese python (Python molurus) and its unique feeding habit of eating at infrequent intervals (several times a year), on large meals (often exceeding the creature's body mass), are associated with large intestinal responses. Specifically, within 24 to 48 hours after eating, the python experiences a 2.5 fold-increase in intestinal mucosal mass, a six-fold increase in microvillus length, and 25 to 100-fold increases in metabolic rate and plasma hormone and lipid levels. In total, the overall gastrointestinal response is twice that of a mammal laboratory animal, making this species ideal for study (the researchers selected the python knowing that any conclusions reached would have to be tested in a mammal subject).
Mice, rabbits, rats, and dogs have all served science by taking their place as mammalian models for study of human physiological processes. However, despite the use of live animal subjects, the digestive process, or the gastrointestinal response to food, has remained unclear. Essentially, these conventional laboratory animals feed frequently on small meals and therefore are always constantly digesting and express only modest activity of gastrointestinal performance.
The Study
The authors of "Luminal Nutrient Signals for Intestinal Adaptations in Pythons" are Stephen M. Secor, John S. Lane, Edward E. Whang, Stanley W. Ashley, and Jared Diamond, all from the University of California-Los Angeles School of Medicine, Los Angeles, California. Their findings appeared in the December 2002, edition of American Journal of Physiology-Gastrointestinal and Liver Physiology.
Methodology
Burmese pythons are indigenous to the subtropical regions of Southeast Asia and feed in the wild chiefly on birds and mammals. They are one of the largest snake species, reaching lengths up to six meters and masses to 100 kilograms. The reptiles used in this study were secured from a commercial breeder and maintained on biweekly diet of laboratory rats and water. Key stages of the experiment included:
- Tests for luminal nutrient signal: Inserting a rubber catheter in the small intestines of 21 pythons followed by a solution allowed post-mortem examination of the organ's mass, morphology, and nutrient uptake values, and compared the findings against a control group.
- Tests for signals other than luminal nutrients: To determine the potential regulatory role of other signals, the researchers (1) identified the cephalic (cranial) phase response on the small intestine; and (2) measured small intestine stretching through placement of a balloon catheter into the organ.
Results
Python intestine failed to respond trophically or functionally to luminal infusions of saline, glucose, lipid, or bile. Infusion of amino acids and peptides, with or without glucose, induced an intermediate response. Infusion of nutritionally complete liquid formula or natural diet induced full intestinal response. Intact meals triggered full intestinal responses without pancreatic or biliary secretions, whereas direct cephalic and gastric stimulation failed to elicit any response. Hence neither physical stimulation (cephalic, gastric, or intestinal) nor the luminal presence of glucose, lipids, or bile can induce intestinal response; instead, a combination of nutrients is required (even without pancreaticobiliary secretions), the most important being amino acids and peptides.
Significant is the finding that amino acids/peptides play a significant response to ingested nutrients. This could be explained that the giant snake's natural meal of live birds and mammals provides a high protein diet, with much less fat and few carbohydrates.
Conclusions
Advantages for using the python in gastrointestinal studies included observance of the creature's large regulatory span, the ease of surgical procedures during the experiment, and the disassociation between functional and trophic (nutritional) responses. The authors suggest that additional experiments be conducted with pythons to determine nutrient response to isolated intestinal loops, upstream or downstream induction of intestinal adaptation, and regulation of intestinal function by gastrointestinal peptides, and intestinal response to regulatory peptides.
The scientific community continues to debate the efficacy and safety of recommended diets for millions of Americans who are classified as obese. The answer to good health may lie in selecting food that is effectively digested by our gastrointestinal system – and the laboratory animal holding the key could be the python.
Source: December 2002, edition of American Journal of Physiology-Gastrointestinal and Liver Physiology. The journal is one of 14 published monthly by the American Physiological Society (APS).
The American Physiological Society (APS) was founded in 1887 to foster basic and applied science, much of it relating to human health. The Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals every year.