Aging and glucose transporter plasticity in response to hypobaric hypoxia

In order to gain a better understanding of tissue plasticity with aging, we investigated the adaptive responses of young and adult animals to both 7 a nd 28 days of hypobaric hypoxia. Senescence is associated with a decreased tolerance to hypoxia that may be related to an age-associated decline in gl ucose transporter system plasticity. In addition, elucidation of the factor s contributing to the decreased hypoxia tolerance with aging may provide in sights into ischemia for older individuals. Following 7 days of hypobaric h ypoxia, soleus and plantaris muscle Glut-4 contents were increased 23-45% w ith a greater increase in the soleus muscle for both ages. A parallel decli ne in insulin receptor content was observed in both the young (soleus 56%: plantaris 74%) and adult (soleus 26%; plantaris 37%) animals over 7 days. S imilar responses were observed in cardiac muscle over 7 days, with increase s in content for both Glut-4 (young 25%; adult 23%) and Glut-1 (young 33%; adult 44%) and a decline in insulin receptor (young 27%; adult 15%). Follow ing 28 days of hypobaric hypoxia, adult soleus, and both age groups plantar is muscle Glut-1 and insulin receptor contents were similar to control. How ever. the young soleus muscle Glut-4 and insulin receptor contents were sti ll significantly different from control but only altered about half as much as following 7 days of exposure to hypobaric hypoxia. In contrast to what was: observed for skeletal muscle, cardiac Glut-4 content was further eleva ted in both young (33%) and adult (44%) animals with longer exposure to hyp obaric hypoxia. The young animals also showed a further decrease in heart i nsulin receptor content, while the adult did not. Interestingly. cardiac Gl ut-1 levels returned to normal values for both young and adult animals with prolonged exposure. An adaptive coregulation of Glut-4 and insulin recepto r content appears to optimize the use of glucose during chronic hypobaric h ypoxia within these tissues. Differences are apparent in the magnitude and time course of the response between young and adult animals. (C) 2001 Elsev ier Science Ireland Ltd. All rights reserved.