Morphological and metabolic adjustments in the small intestine to energy demands of growth, storage, and fasting in the first annual cycle of a hibernating lizard (Tupinambis merianae).

Seasonal plasticity in the small intestine of neonatal tegu lizards was investigated using morphometry and analysis of enzymes involved in supplying energy to the intestinal tissue. In the autumn, the intestinal mass (Mi) was 1.0% of body mass and the scaling exponent b=0.92 indicated that Mi was larger in smaller neonates. During arousal from dormancy Mi was 23% smaller; later in spring, Mi increased 60% in relation to the autumn and the exponent b=0.14 indicated that the recovery was disproportionate in smaller tegus. During the autumn, the intestinal villi were greatly elongated; by midwinter, the Hv, SvEp, and VvEp were smaller than during the autumn (59%, 54%, 29%) and were restored to autumn levels during spring. In the active tegus, the maximum activity (Vmax) of enzymes indicated that the enterocytes can obtain energy from different sources, and possess gluconeogenic capacity. During winter, the Vmax of CS, HOAD, GDH, PEPCK was 40-50% lower in relation to the autumn and spring, while the Vmax of HK, PK, LDH, AST was unchanged. The hypoglycemia and the mucosal atrophy/ischemia during winter would prevent the enterocytes from using glucose, whereas they could slowly oxidize fatty acids released from body stores and amino acids from the tissue proteolysis to satisfy their needs of energy. Contrastingly, starvation during spring caused severe mass loss (50%); the tissue protein and the VvEp and VvLP did not change while the thickness of the muscular layer increased 51%, which suggested different effects along the length of the organ. In addition, the Vmax of the glycolytic enzymes was lower, indicating that a regulatory mechanism would spare blood glucose for vital organs during unanticipated food restriction.

Cardiac hypertrophy and structural and metabolic remodeling related to seasonal dormancy in the first annual cycle in tegu lizards.

Morpho-functional adjustments in the heart of juvenile tegu lizards (Tupinambis merianae) were analyzed at distinct seasonal periods to investigate how the demands of growth and of energy saving are reconciled during the first annual cycle. The relative ventricular mass (Mv) was 31% and 69% larger in late autumn and winter dormancy, respectively, compared to early autumn. This effect did not persist during unfed arousal, suggesting that protein accumulates in the heart during hypometabolism and is degraded on arousal. Both the hypertrophy and the atrophy were disproportionate in the largest individuals. In contrast, Mv was smaller in lizards that were starved during spring activity compared to fed lizards, this effect being larger in smaller individuals. In late autumn and winter dormancy the spongy myocardium had 8% of the section area covered by lacunary spaces, which expanded after food intake during arousal and reached 29% in spring activity together with higher density of cardiomyocytes. Total and soluble proteins per mass unity were unchanged, and maximum activities of selected enzymes suggest sustained glycolytic and aerobic capacities during hypometabolism. Results indicate that important structural adjustments occur in the heart in anticipation of dormancy, and that the protein balance in the tissue is maintained at winter temperatures ~17°C.