Ups and downs of intestinal function with prolonged fasting during aestivation in the burrowing frog, Cyclorana...

Although green striped burrowing frogs (Cyclorana alboguttata) experience large reductions in the mass and absorptive surface area of the small intestine (SI) during aestivation, little is known about how this may affect the functional capacity of the SI. We examined changes in the function (l-proline uptake rate and capacity) and metabolism of the SI (in vitro oxygen consumption, Na(+)/K(+)-ATPase activity and abundance) of C. alboguttata following 6 months of aestivation. l-Proline uptake rate was significantly higher in aestivating frogs, but overall uptake capacity was lower than in active frogs. Total SI oxygen consumption rate (V(O(2))) was also lower in aestivating frogs, despite no difference in mass-specific V(O(2)). The proportion of intestinal V(O(2)) associated with Na(+)/K(+)-ATPase activity and protein synthesis was equivalent between active and aestivating frogs, suggesting these processes were unaffected by aestivation. Indeed, the activity of Na(+)/K(+)-ATPase transporters in the SI of aestivating frogs was not different from that of active animals. Aestivating frogs maintained Na(+)/K(+)-ATPase activity, despite experiencing a reduction in the density of Na(+)/K(+)-ATPase transporters, by increasing the molecular activity of the remaining pumps to 2-3 times that of active frogs. These results show that functionality of the SI is maintained at the cellular level, potentially facilitating the reclamation of nutrients from the intestinal lumen while in aestivation. Despite this, the functional capacity of the SI in aestivating C. alboguttata is significantly reduced due to a reduction in tissue mass, helping frogs to conserve energy while in aestivation.