Effect of Hypoxia on Norepinephrine of Various Tissues in Rats

Abstract

To determine the effects of hypoxia and hypoxic exercise (HE) on the norepinephrine levels of various tissues in rats. Male Wistar rats were randomly assigned to 3 groups: an HE group (n = 6), a hypoxic-sedentary (HS) group (n = 6), and a normoxic-sedentary (NS) group (n = 6). The HE rats had access, ad lib, to an exercise wheel for 8 weeks. HE and HS rats were maintained in a normobaric hypoxic chamber with an FIO2 of 16%. Norepinephrine levels were measured and compared in liver, heart, diaphragm, soleus, and gastrocnemius tissues from the 3 groups. Liver norepinephrine levels in the HE and HS groups were significantly lower than the levels in the NS group (P < .05). No significant difference was found in liver norepinephrine levels between the HE and the HS groups. The heart norepinephrine levels in the NS group were significantly lower than the levels in the HE (P < .01) and HS groups (P < .01). In contrast, no significant differences were found in the norepinephrine levels for the diaphragm and soleus muscle among the 3 groups. The norepinephrine levels in the gastrocnemius white muscles were significantly higher in the HS group than in the HE (P < .05) and NS groups (P < .01). P < .01 represents a significant difference at the level of 1%. This study demonstrated that hypoxia and HE both elicit a decreased sympathetic response in the liver tissue of male Wistar rats but cause an increased response in heart tissue. These results suggest that the sympathetic responses to long-term hypoxia and HE training are different in various rat tissues.