Effect of the association between hypoxia and phase of day on body temperature in rats

Author(s)

Carolina da Silveira Scarpellini

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2011-10-11

Examining board members

Kênia Cardoso Bícego; Maria Camila Almeida; Luiz Silveira Menna Barreto

• Advisor: Kênia Cardoso Bícego

Abstract

Several animals face reduced oxygen partial pressure (hypoxia) throughout their lives, due to environmental (burrows, high altitudes) or clinical conditions (cardiac, respiratory or metabolic failures). Its known that the hypoxia-induced decrease in body temperature (Tb), named anapyrexia, is a regulated process of adaptive importance. However only in the past few decades researchers have been studied the mechanisms involved in this phenomenon. These studies, in general, did not take the phase of the day into account during the experiments or during the analyses of their results. Considering that Tb shows circadian and diary rhythm with a robust pattern, it is possible that anapyrexia can be altered depending on to the moment of the day in which the animal is exposed to hypoxia. Thus, the present study tested this hypothesis exposing animals to hypoxia in different phases of Day and Tb, oxygen consumption (VO2) and heat loss index (HLI) were measured. These protocols were conducted in two ambient temperatures (Tas; 26°C and 19°C), because it is known that anapyrexia can be altered by Ta. In both Tas, it was observed that animals exposed to hypoxia during the beginning of the dark phase presented bigger anapyrexic amplitude than those exposed during the beginning of the light phase. This difference may be due, at least in part, to the inhibition induced by hypoxia of the biggest thermogenesis found during dark phase. HLI measured at the end of the hypoxia exposure seems to have no influence in the different anapyretic responses. Moreover, the cold condition induced bigger anapyretic responses independent on the phase of day. Thus, the results indicate the phase of day influences the hypoxia-induced anapyrexia and this response is bigger in lower ambient temperatures at any moment of the light-dark cycle. (AU)

• FAPESP's process: 08/07698-5 - Interaction between kappa opioid receptor activation and nitric oxide/cGMP pathway in the central nervous system for the development of hypoxia-induced anapyrexia
• Grantee: Carolina da Silveira Scarpellini
• Support Opportunities: Scholarships in Brazil - Master