Reduced insulin secretion and glucose intolerance are involved in the fasting susceptibility of common vampire bats.

Susceptibility during fasting has been reported for the common vampire bat (Desmodus rotundus), to the point of untimely deaths after only 2-3 nights of fasting. To investigate the underlying physiology of this critical metabolic condition, we analyzed serum insulin levels, pancreatic islets morphometry and immunocytochemistry (ICC), static insulin secretion in pancreas fragments, and insulin signaling mechanism in male vampire bats. A glucose tolerance test (ipGTT) was also performed. Serum insulin was found to be lower in fed vampires compared to other mammals, and was significantly reduced after 24h fasting. Morphometrical analyses revealed small irregular pancreatic islets with reduced percentage of ß-cell mass compared to other bats. Static insulin secretion analysis showed that glucose-stimulated insulin secretion was impaired, as insulin levels did not reach significance under high glucose concentrations, whereas the response to the amino acid leucin was preserved. Results from ipGTT showed a failure on glucose clearance, indicating glucose intolerance due to diminished pancreatic insulin secretion and/or decreased ß-cell response to glucose. In conclusion, data presented here indicate lower insulinemia and impaired insulin secretion in D. rotundus, which is consistent with the limited ability to store body energy reserves, previously reported in these animals. Whether these metabolic and hormonal features are associated with their blood diet remains to be determined. The peculiar food sharing through blood regurgitation, reported to this species, might be an adaptive mechanism overcoming this metabolic susceptibility.

Effect of fasting on carbohydrate metabolism in frugivorous bats (Artibeus lituratus and Artibeus jamaicensis).

The compensatory changes of carbohydrate metabolism induced by fasting were investigated in frugivorous bats, Artibeus lituratus and Artibeus jamaicensis. For this purpose, plasma levels of glucose and lactate, liver and muscle glycogen content, rates of liver gluconeogenesis and the activity of related enzymes were determined in male bats. After a decrease during the first 48 h of fasting, plasma glucose levels remained constant until the end of the experimental period. Plasma lactate levels, extremely high in fed bats, decreased after 48 h of fasting. Similarly, liver glycogen content, markedly high in fed animals, was reduced to low levels after 24 h without food. Muscle glycogen was also reduced in fasted bats. The expected increase in liver gluconeogenesis during fasting was observed after 48 h of fasting. The activities of liver glucose-6-phosphatase and fructose-1,6-bisphosphatase were not affected by food withdrawn. On the other hand, fasting for 24 h induced an increase in the activity of liver cytosolic phosphoenolpyruvate carboxykinase. The data indicate that liver gluconeogenesis has an important role in the glucose homeostasis in frugivorous bats during prolonged periods of food deprivation. During short periods of fasting liver glycogenolysis seems to be the main responsible for the maintenance of glycemia.

Effects of short-term fasting on energy reserves of vampire bats (Desmodus rotundus).

Studies on metabolic responses to fasting in common vampire bats (Desmodus rotundus) have demonstrated the susceptibility of this species when subjected to long-term fasting. We investigated the effects of short-term fasting (12 h), a period similar to what they face in the field, on their energy reserves. Blood glucose (BG) levels in fed bats were similar to other mammals, but after 12 h without food, these levels were reduced. Plasma lactate and free fatty acids levels in fed bats were higher than in other mammals, although no changes in these levels were detected in response to fasting. Liver glycogen content decreased significantly following fasting. Muscle glycogen, as well as liver and muscle lipid and protein levels, remained unaltered for up to 12 h of fasting. Although BG levels decreased after short-term fasting, body energy reserves do not seem to play an important role for maintenance of glycemic homeostasis during fasting. Despite the decrease in liver glycogen, this small reserve seems insufficient to maintain adequate levels of BG, even during short periods of fasting. Because other reserves were not decreased after fasting, it is possible that the main source of glucose for common vampire bats might be the glucose content of their blood diet.