Effect of fasting in the digestive system: histological study of the small intestine in house sparrows.

In birds and mammals the metabolic response to fasting has been studied and can be characterized by three consecutive phases reflecting metabolic and physiological adjustments. An effective way to minimize energy expenditure during food scarcity is to decrease the mass of the organs. As the digestive system is metabolically expensive to maintain, the small intestine and the liver are the most affected organs. We evaluated the effects of phase III starvation on the mass of the different organs and histological parameters on house sparrows, a small non-migrant bird. In a short period of time (34 h) we observed a larger reduction in the digestive organ mass when compared to the mass of the body and non-alimentary tissues. Furthermore, the intestinal mass was proportionally more reduced than its length and nominal surface area. A reduction on the intestinal mucosal layer also resulted in a shortening of villus (length and thickness) and crypt depth. Moreover, the morphology of the enterocytes changed from cylindrical to cubical, suggesting that the surface exposed to the lumen was conserved. This may indicate an adaptive response to the moment of refeeding. The nominal surface area/body mass remained constant in both groups and several histological parameters were reduced, suggesting that starving induces the atrophy of the small intestine. However, the goblet cells were conserved after fasting indicating a protective tendency.

Effect of fasting on the structure and function of the gastrointestinal tract of house sparrows (Passer domesticus).

Starvation is a condition that often affects animals in nature. The gastrointestinal tract is the organ system displaying the most rapid and dramatic changes in response to nutrient deprivation. To date, little is known about starvation phases and effects on the organ morphology and digestive function in small passerine birds. In this study, we determined the phases of starvation and examined the effect of final stage of starvation in the organ morphology and, intestinal histology and enzymatic function in the small intestine. Our results show the three phases of the classical model of fasting in a shorter period of time. The mass of heart, pancreas, stomach, small intestine and liver of long-term fasted birds was reduced between 20 and 47%. The mass decrease in small intestine was correlated with reduction in small intestinal histology: perimeter, mucosal thickness, villus height and width. In contrast, the enzyme activity of sucrase-isomaltase and aminopeptidase-N in enterocytes, all expressed per µg of protein, was higher in long-term fasted birds than fed animals. This suggest that, while autophagy of digestive organs is induced by starvation, consistent with phenotypic plasticity, the activity of sucrase-isomaltase and aminopeptidase-N remains high, probably as an anticipatory strategy to optimize digestion at re-feeding time.

Contamination of heavy metals in birds from Embalse La Florida (San Luis, Argentina).

Embalse La Florida is an artificial lake located in midwestern Argentina's San Luis province. It provides drinking water to approximately 70% of the province's human population and approximately 20% of the province is irrigated with water from the reservoir. The presence of heavy metals in Embalse La Florida's water has previously been reported. Nevertheless, no information about the levels of these contaminants in birds is available for this region. The aim of this study, therefore, is to (1) establish baseline data on lead (Pb) and cadmium (Cd) levels in birds from Embalse La Florida, (2) assess metal accumulation patterns between organs and bird species, and (3) evaluate the potential risk that these heavy metals pose for the local avifauna. We measured Pb and Cd in bone, pectoralis muscle, liver, gonad, and brain of three bird species representative of the Embalse La Florida ecosystem: Podiceps major (Great Grebe), Phalacrocorax brasilianus (Neotropic Cormorant), both of which are piscivorous, and Pitangus sulphuratus (Great Kiskadee), which is omnivorous. We also measured both heavy metals in Great Grebe eggs. Pb and Cd were detected in all of the tissues we assayed, and Pb concentrations were significantly higher than those for Cd in all tissues. The patterns of Pb and Cd accumulation differed between tissues, however. In general, gonads had the highest concentrations of Pb while Cd tended to accumulate in the liver. An interspecific analysis revealed that the omnivorous species had higher levels of both metals in bone, liver, and brain compared to both piscivorous species. There were no differences in Pb and Cd concentrations between males and females. The highest liver level of Pb (4.69 ppm wet weight) detected in Great Kiskadee, was comparable to those associated with toxic effects in birds, and Pb concentrations found in the liver of two females and two males (2.07 to 2.32 ppm wet weight) were also similar to those that could be physiologically detrimental in other species. In all birds assayed, Cd levels in liver tissue were lower than those typically shown to be harmful. Our results indicate that Great Kiskadees are highly polluted by Pb and their exposure to this contaminant exceeds the level reported to trigger adverse effects. This is the first study to assay heavy metals in birds from midwest Argentina and provides a starting point for studies examining the impact that these metals have on both wildlife and humans in the region.