Insulin resistance in older rats

Area of Science:

• Metabolic Physiology
• Aging Research
• Endocrinology

Background:

• Insulin is a key hormone regulating glucose metabolism.
• Age-related changes can impact insulin sensitivity and glucose disposal.
• Understanding these changes is crucial for metabolic health.

Purpose of the Study:

• To investigate the effects of aging on in vivo and in vitro insulin-stimulated glucose utilization in rats.
• To examine age-related alterations in muscle enzyme activities involved in glucose metabolism.
• To correlate changes in body weight with insulin action and glucose disposal efficiency.

Main Methods:

• Insulin suppression test to assess in vivo glucose utilization.
• Perfused hindlimb preparations to measure in vitro glucose uptake.
• Analysis of key glycolytic and glycogenolytic enzyme activities in soleus muscle.

Main Results:

• Older rats (12 mo) exhibited significantly higher steady-state plasma glucose (SSPG) concentrations compared to younger rats (1.5 and 4 mo), indicating reduced insulin sensitivity.
• In vitro insulin-stimulated glucose uptake in hindlimbs of 12-mo-old rats was approximately 50% lower than in 1.5-mo-old rats.
• Soleus muscle showed increased glycogen synthase and decreased glycogen phosphorylase activity with age, and muscle glycogen content was elevated in older rats.

Conclusions:

• Aging in rats is associated with a progressive decline in insulin-stimulated glucose utilization, both in vivo and in vitro.
• Age-related changes in muscle enzyme activity, including altered glycogen metabolism, contribute to impaired glucose disposal.
• These findings highlight the significant impact of aging on glucose homeostasis and insulin action.