Taxa metabólica e expressão do gene hif-1α em juvenis e adultos do ciclídeo amazônico Astronotus ocellatus em condição de hipóxia aguda

Abstract

The Amazonian floodplain lakes face daily fluctuations in oxygen concentrations, ranging from supersaturation during the day to almost total lack of oxygen during the night and, moreover, the greatest amount of oxygen is located at the first centimeter of the water column. The ichthyofauna of these environments developed different adjustments to deal with low oxygen levels, like behavioral, physiological, biochemical and molecular mechanisms, and these strategies may be different over the development of the individual. The objective of this study was to investigate, at a physiological and molecular level, how juveniles and adults of the cichlid Astronotus ocellatus deal with exposure to acute hypoxia. For this, the mass-specific oxygen consumption, critical oxygen level (Pcrit), plasma glucose and lactate, liver glycogen and hif-1α gene transcription of juveniles weighing 10g, 50g and 100g, and adults weighing 500g were analyzed. Our results showed a hypoallometric relationship between mass-specific oxygen consumption and fish body mass, with an allometric exponent equal -0.26 (or 0.74). When exposed to five hours acute hypoxia, juveniles and adults reduced their aerobic metabolism, however, juveniles needed to activate the fermentative pathway for energy supply, once plasma glucose and lactate increased in this group, while adults relied only on metabolic suppression as a mechanism to maintain in equilibrium the demand and supply of energy, since they did not show any change on plasma glucose and lactate. Juveniles and adults exposed to normoxia and acute hypoxia had the same hif-1α transcripts levels in liver, except 100g juveniles, that showed an increase on hif-1α transcripts level when exposed to acute hypoxia. This result may be a consequence of their lower capacity to extract the oxygen under hypoxia, evidenced by their higher Pcrit value, and thus acute hypoxia exposure was stronger for these animals. The transcripts levels of hif-1α in the gills were the same between groups and treatments. Since the gills of A. ocellatus do not have their oxygen extraction impaired by acute hypoxia exposure, an increase on hif-1α transcripts levels was not necessary. This study was one of the few studies to address the hif-1α transcripts levels along the developmental stages and further analysis of the HIF-1α protein will provide more information about the molecular mechanisms of this unique hypoxia and anoxia-tolerant Amazonian cichlid.