Structural and metabolic reorganization of the gut during the fasting and seasonal dormancy in tegu lizards Tupinambis merianae / Reorganização estrutural e metabólica do intestino associada ao jejum e dormência sazonal em lagartos teiú Tupinambis merianae

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

The gut phenotypic plasticity is widely documented in the vertebrates and would allow to either short term or anticipatory adjustments in the organ functional capacity, to cope with unpredictable and periodic changes of food availability in the environment. This study investigates seasonal changes of morphology and in the capacity for substrate oxidation in the midgut of the tegu lizard Tupinambis merianae, associated with prolonged fasting and metabolic depression in winter months. In addition, the pattern of change was compared with the adjustments induced by 20 days of fasting in spring active animals. Groups of young lizards were killed in distinct phases during the first annual cycle and the midgut was quickly excised and weighted. Tissue samples were removed from the organ proximal third and preserved in fixative solution for histology. The remaining tissue was cut in small pieces and aliquots were frozen in liquid N2 and stored at -80oC for the assays. The morphological changes were analyzed in 5μm thick slices using stereological methods. The content of water and of total and soluble proteins were measured using standard assays, and maximum activities of metabolic enzymes were measured by espectrophotometry. The mid-gut mass is 1.04% of body mass in autumn activity and decreases 23% during winter dormancy, combined with a reduction of mucosal volume and surface densities, of villus maximal height and of total protein content. The epithelial cells change conformation from columnar to pseudo-stratified, suggesting intense proliferative activity during dormancy. Later in spring activity, the mid-gut mass increases to 1.64% combined with an increase of epithelial surface density and possibly of midgut lenght and/or diameter. Atrophy during fasting was higher in active lizards, 49% in relation to fed animals, the mucosal density however is more preserved than during dormancy and the muscle layer increases thickness. High levels of enzyme activities suggest a potential to obtain energy from different substrates and the regulatory mechanisms of fuel selection would act as a function of the physiological context. HK, PK and LDH, and AspAT, acting on pathways of glucose and amino-acid oxidation respectively, do not change during the annual cycle, whereas GDH and HOAD (amino-acid and fatty acid oxidation respectively), and CS (indicator of mitochondrial aerobic capacity) are strongly inhibited in dormant and arousing animals. Fasting during spring activity caused all enzymes to be inhibited and this effect, together with large tissue atrophy, suggest that in the short term fasting the regulatory mechanisms allow to save glucose for glucose-dependent tissues, besides contributing to energy spare at the whole body level.

ASSUNTO(S)

dormência sazonal midgut lizard plasticidade fenotípica seasonal dormancy intestino phenotypic plasticity fasting tupinambis merianae tupinambis merianae jejum lagarto

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