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First published online September 14, 2007
Journal of Experimental Biology 210, 3430-3439 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.004820

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Metabolic and digestive response to food ingestion in a binge-feeding lizard, the Gila monster (Heloderma suspectum)

C. M. Christel^1,*, D. F. DeNardo¹ and S. M. Secor²

¹ Arizona State University, School of Life Sciences, PO Box 874501, Tempe, AZ 85287, USA
² University of Alabama, Department of Biology, 420 Biology Building, Tuscaloosa, AL 35487, USA

View larger version (6K): [in this window] [in a new window]   Fig. 1. Mean rates of oxygen consumption (O2) of Heloderma suspectum prior to (day 0) and following the consumption of rodent meals, rodent meals fed under anesthesia, or egg meals equaling 10% of lizard body mass (N=6 for each meal). Values are means ±1 s.e.m.

View larger version (23K): [in this window] [in a new window]   Fig. 2. Mass of stomach and small intestinal contents of Heloderma suspectum at 1 and 3 days following the consumption of rodent meals equal in mass to 10% of lizard body mass. For each meal treatment, ingested meals averaged 44.2 g. Meal treatments include 1 day postfeeding of rodent meal (1DPF), 1 day postfeeding of rodent meal under anesthesia (1DPF-anes), and 3 days postfeeding of rodent meal (3DPF). Values are means ±1 s.e.m.

View larger version (20K): [in this window] [in a new window]   Fig. 3. Small intestine mass (A) and length (B) of fasted and fed Heloderma suspectum. For details of meal treatments, see Fig. 2. Values are means ±1 s.e.m., N=3 for each fasted and fed treatment.

View larger version (53K): [in this window] [in a new window]   Fig. 4. (A) Thickness of the proximal intestine mucosa and muscularis/serosa layers and (B) micrographs of the intestinal epithelium of fasted and fed Heloderma suspectum (1DPF). For details of meal treatments, see Fig. 2. Scale bars, 200 µm; Values in A are means ±1 s.e.m., N=3 for each fasted and fed treatment. Different letters above the bars denote significant differences between means (for P values, see text). For each fed treatment intestinal mucosa had significantly increased in thickness, whereas the muscularis/serosa layer did not change.

View larger version (26K): [in this window] [in a new window]   Fig. 5. Height (A), width (B), volume (C) and micrographs (D) of intestinal enterocytes from the proximal small intestine of Heloderma suspectum. Values are means ±1 s.e.m., N=3 for each fasted and fed treatment. Different letters above the bars denote significant differences between means. Scale bars in D, 20 µm. Heloderma suspectum experience a significant increase in enterocyte width and volume 1 day after feeding (1DPF), and a further increase in width and volume by day 3 of digestion (3DPF). For details of meal treatments, see Fig. 2.

View larger version (21K): [in this window] [in a new window]   Fig. 6. Aminopeptidase-N activity of the proximal small intestine of fasted and fed Heloderma suspectum. Feeding resulted in a significant increase in aminopeptidase-N activity, which was further elevated for lizards that had consumed meals while under anesthesia. For details of meal treatments, see Fig. 2.

View larger version (22K): [in this window] [in a new window]   Fig. 7. Uptake rate of L-leucine (A), L-proline (B) and D-glucose (C) of the proximal, middle and distal portions of the small intestine of fasted and fed Heloderma suspectum. For details of meal treatments, see Fig. 2. Values are means ±1 s.e.m., N=3 for each fasted and fed treatment. Different letters above the bars denote significant differences between means (see text for P values). There was no detectable uptake of D-glucose for the distal small intestine of fasted lizards; therefore, no bar is shown. Lizards experienced no significant postprandial increase in L-leucine and L-proline uptake, whereas D-glucose uptake increased significantly with feeding in the proximal and middle small intestine.

View larger version (19K): [in this window] [in a new window]   Fig. 8. Total intestinal uptake capacity of L-leucine (A), L-proline (B) and D-glucose (C) of fasted and fed Heloderma suspectum. For details of meal treatments, see Fig. 2. Values are means ±1 s.e.m., N=3 for each fasted and fed treatment. Different letters above the bars denote significant differences between means. Each feeding treatment experienced significant increases in uptake capacity for the three nutrients.

View larger version (6K): [in this window] [in a new window]   Fig. 9. Specific dynamic action (SDA, in kJ) plotted against meal energy (kJ) for 11 species of lizards. The log plot was used for convenience in visualizing the range of data. On average, SDA was equivalent to 17.5% of meal energy. Numbers signify the following species and their meal type: 1, Sceloporus merriami – cricket meal (Beaupré et al., 1992); 2, Anolis carolinensis – beef meal (Coulson and Hernandez, 1983); 3, Sceloporus occidentalis – cricket meal (Roe et al., 2005); 4, Eulamprus tympanum – mealworm meal (Robert and Thompson, 2000); 5, Sphenomorphus indicus – mealworm meal (Hong-Liang et al., 2004); 6, Eumeces chinensis – frog meal (Pan et al., 2005); 7, Eumeces chinensis – mealworm meal (Pan et al., 2005);8, Eulamprus quoyii – mealworm meal (Iglesias et al., 2003); 9, Varanus exanthematicus – rodent meal (Hicks et al., 2000); 10, Tubinambis merianae – beef meal (Klein et al., 2006); 11, Varanus albigularis – egg meal (Secor and Phillips, 1997); 12, Varanus albigularis – turkey/snail meal (Secor and Phillips, 1997); 13, Varanus albigularis – rodent meal (Secor and Phillips, 1997).

View larger version (111K): [in this window] [in a new window]   Fig. 10. Transmission electron micrographs of the intestinal brush border membrane of fasted and fed Heloderma suspectum. Scale bars, 1 µm. Note the presence of fat droplets within the enterocytes at 1 day postfeeding (1DPF) and the apparent lengthening of microvilli by day 3 of digestion (3DPF).